Structural Integrity and Monitoring for Composite Materials 9811962812, 9789811962813

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Composites Science and Technology

Ahmad Hamdan Ariffin Noradila Abdul Latif Muhammad Faisal bin Mahmod Zaleha Binti Mohamad   Editors

Structural Integrity and Monitoring for Composite Materials

Composites Science and Technology Series Editor Mohammad Jawaid, Laboratory of Biocomposite Technology, Universiti Putra Malaysia, INTROP, Serdang, Malaysia

This book series publishes cutting edge research monographs comprehensively covering topics in the field of composite science and technology. The books in this series are edited or authored by top researchers and professional across the globe. The series aims at publishing state-of-the-art research and development in areas including, but not limited to: • • • • • • • • • • • •

Conventional Composites from natural and synthetic fibers Advanced Composites from natural and synthetic fibers Chemistry and biology of Composites and Biocomposites Fatigue damage modelling of Composites and Biocomposites Failure Analysis of Composites and Biocomposites Structural Health Monitoring of Composites and Biocomposites Durability of Composites and Biocomposites Biodegradability of Composites and Biocomposites Thermal properties of Composites and Biocomposites Flammability of Composites and Biocomposites Tribology of Composites and Biocomposites Applications of Composites and Biocomposites

Review Process The proposal for each volume is reviewed by the main editor and/or the advisory board. The chapters in each volume are individually reviewed single blind by expert reviewers (at least two reviews per chapter) and the main editor. Ethics Statement for this series can be found in the Springer standard guidelines here - https://www.springer.com/us/authors-editors/journal-author/journal-aut hor-helpdesk/before-you-start/before-you-start/1330#c14214

Ahmad Hamdan Ariffin · Noradila Abdul Latif · Muhammad Faisal bin Mahmod · Zaleha Binti Mohamad Editors

Structural Integrity and Monitoring for Composite Materials

Editors Ahmad Hamdan Ariffin Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia Batu Pahat, Malaysia

Noradila Abdul Latif Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia Batu Pahat, Malaysia

Muhammad Faisal bin Mahmod Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia Batu Pahat, Malaysia

Zaleha Binti Mohamad Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia Batu Pahat, Malaysia

ISSN 2662-1819 ISSN 2662-1827 (electronic) Composites Science and Technology ISBN 978-981-19-6281-3 ISBN 978-981-19-6282-0 (eBook) https://doi.org/10.1007/978-981-19-6282-0 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

Composite materials may be subject to delamination, matrix cracking, and other concurrent or sequential damage processes that manifest at various sizes. A major obstacle to preventing the impacts of the damage modes on the overall structural health is the earlier damage detection and identification. Through the integration of onboard inspection technologies adapted from Non-Destructive Evaluation (NDE), which uses fully developed techniques like ultrasonics, X-rays, or thermography inspections, Structural Health Monitoring (SHM) intends to boost the safety of structures and reduce control downtime. The SHM techniques are not only limited to in-service data collecting provided by a distributed sensor network permanently attached to the surface or embedded inside the monitored structure and are necessary to assess the structure’s damage state using complex algorithms and damage models. The technology is discussed thoroughly in a few chapters to give a good insight into the application. Besides that, composite as an anisotropic material faces real challenges for SHM application. The characteristics of the engineering composite part may not be precisely identified, and the content has uneven uniformity. Therefore, the understanding of the composite application and natural fibre is reported. The fabrication process for synthetic, hybrid, and natural fibre composite is presented thoroughly as guidance to the reader. Batu Pahat, Malaysia

Ahmad Hamdan Ariffin Noradila Abdul Latif Muhammad Faisal bin Mahmod Zaleha Binti Mohamad

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Contents

Structural Health Monitoring of Laminated Materials for Aerospace Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gérald Franz and Muhammad Hafiz Hassan

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Modeling of Damage Evaluation and Failure of Laminated Composite Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Joy Mathavan, Muhammad Hafiz Hassan, and Gérald Franz

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Damage Detection of Impact-Induced Fiber Glass Laminated Composite (FGLC) Plates Via ANN Approach . . . . . . . . . . . . . . . . . . . . . . . M. F. Mahmod, Elmi Abu Bakar, and A. R. Othman

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Microperforated Panel Made by Biodegradable Natural Fiber Composite for Acoustic Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Desmond Daniel Vui Sheng Chin, Musli Nizam bin Yahya, and Nazli bin Che Din Fractographic Investigation and Mechanical Properties of Novel 7xxx Al-Alloy from Recycled Beverage Cans (RBCs) for Automotive Components Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Kazeem, H. N. Awwal, N. Z. Hassan, N. A. Badarulzaman, S. S. Jikan, and W. F. F. Wan Ali Condition Monitoring of Wood Polymer Composite for Civil Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nur Afiqah Sufian, Anika Zafiah Mohd Rus, Nurul Syamimi A. Salim, and Hendi Saryanto

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Synthetic, Hybrid and Natural Composite Fabrication Processes . . . . . . . 115 Onur Agma and Suleyman Basturk

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Contents

Application of Composite for Engineering Application . . . . . . . . . . . . . . . . 139 Muhammad Zuhair Mohd Abdul Rahman, Ahmad Hamdan Ariffin, Syariful Syafiq Shamsudin, Mohamad Norani Mansur, Mohammad Sukri Mustapa, and Abdul Rahim Irfan Potential Application of Natural Fibre in the Aviation Industry . . . . . . . . 157 Mohd Fadhli Zulkafli, Muhammad Naim Romzee, Ahmad Hamdan Ariffin, Fairuz Alias, Mohamad Norani Mansur, Mohammad Sukri Mustapa, and Abd Rahim Irfan Natural Fibre for Composite Structural Application . . . . . . . . . . . . . . . . . . 165 Siti Amira Othman, Nur Nadia Nasir, and Nor Farah Amirah Nor Azman Overview of Unmanned Aerial Vehicle (UAV) Parts Material in Recent Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Mohd. Rasidi Ibrahim, Muhamad Firdaus Azman, Ahmad Hamdan Ariffin, Mohamad Norani Mansur, Mohammad Sukri Mustapa, and Abdul Rahim Irfan Characterization of Semi Amorphous Phase of Rice Husk Silica Reinforced AA7075 Aluminium Chips Based Matrix . . . . . . . . . . . . . . . . . . 191 Hoo Wei Wen, Noradila Abdul Latif, Nurul Farahin Mohd Joharudin, and Mohammad Sukri Mustapa Improving the Flexural and Tensile Properties of Reinforced Polypropylene Composites by Using Pineapple Leaf Fibre . . . . . . . . . . . . . 205 Syafiqah Nur Azrie Safri, Muhammad Naim Romzee, Muhammad Adli Zufayri Shamsol, Ahmad Hamdan Ariffin, Fairuz Alias, Mohamad Norani Mansur, Mohammad Sukri Mustapa, Irfan Abdul Rahim, and Mohd. Fadhli Zulkafli Natural Fiber of Palm Empty Fruit Bunches (PEFB) Reinforced Epoxy Resin as Polymer Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Mohamad Mohshein Hashim, Noraini Marsi, Anika Zafiah Mohd Rus, Nur Sahira Marhaini Sharom, and Asmadi Md Said The Development of Temporary Bone Scaffolds from High Density Polyethylene (HDPE) and Calcium Carbonate (CaCO3 ) for Biomedical Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 N. Zulkefli, M. D. Ahmad, S. Mahzan, and E. M. Yusup

About the Editors

Ir. Dr. Ahmad Hamdan Ariffin is currently working as a senior lecturer at Universiti Tun Hussein Onn Malaysia (UTHM). He is head of the Research Centre for Unmanned Vehicle (ReCUV), UTHM. He obtained his Ph.D. in Aerospace Engineering from Universiti Putra Malaysia in 2015. He was awarded a Master of Engineering Science in Advanced Manufacturing from the University of Malaya and did his Bachelor’s Degree in Aerospace Engineering at UPM. His research focuses mainly on turbine blade aerodynamics, structural health monitoring systems, biocomposites fabrication, structure vibration, cutting tool technology, and cooling system. He was awarded with Gold Medal for his project, Automatic Thermocyclic Dipping Machine (ATDM) at ITEX 2011. He also has a few consultation works for some significant projects such as the Automatic Thermocyclic Dipping Machine for CRADLE fund. He was also a manager at Zecttron Sdn. Bhd., which is a University of Malaya spin-off company. He already published 1 book, 5 book chapters, more than 20 proceeding papers and more than 15 International journal papers. Dr. Noradila Abdul Latif is currently working as a senior lecturer at the Department of Mechanical Engineering, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia, as well as a Head of Mechanical Failure Prevention and Reliability Research Centre (MPROVE) and a Chief Editor of Journal of Advanced Mechanical Engineering Applications (JAMEA). She has more than 10 years of experience in teaching and research. Her area of research interests includes failure analysis, metal matrix composite, mechanical testing, impact engineering, materials fabrication and processing. She has several research grants at university and national levels in several research areas. She is a graduate member of Board of Engineering Malaysia (BEM), Microscopy Society Malaysia (MSM) and International Association of Engineering (IAENG). Ts. Dr. Muhammad Faisal bin Mahmod is currently working as Senior Lecturer at the Faculty of Mechanical and Manufacturing Engineering (FKMP), Universiti Tun Hussein Onn Malaysia (UTHM), Batu Pahat, Johor Malaysia, and also has been appointed as a principal researcher in Structural Integrity and Monitoring Research ix

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About the Editors

Group (SIMReG) since 2018. He has more than 10 years of experience in teaching, research, and industries. He is also a member of the Board of Engineers Malaysia (BEM), Malaysia Board of Technologists (MBOT), Malaysian Society for NonDestructive Testing (MSNT), and holds CSWIP UT Welds Level 2 Non-Destructive certificate. His area of research interests includes non-destructive testing, automated control systems, laminated composites, weld, and structural integrity. To date, he has published more than 20 peer-reviewed national and international journal and proceedings papers since 2013 and also obtained 1 Patent titled Automated Pulse Echo Scanning Unit. H-index and citation in Scopus are 4 and 27, and in Google scholar, H-index and citation are 4 and 49. He is also a reviewer of several international peer-reviewed journals and proceedings Scopus indexed; ETIC, ICME, IJIE, SR, and ISCAIE. He is supervising 1 Master’s student in the fields of automated control systems and has more than 15 undergraduate final year projects since 2018 to date. He contributed in several research grants at university, and national levels on non-destructive testing and material integrity of around 200 thousand Malaysian ringgits. Dr. Zaleha Binti Mohamad is currently working at the Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM) and has been appointed as Visiting Lecturer at the Department of Mechanical Engineering, Universitas Muhammadiyah Surakarta since January 2021. She has more than 12 years of experience in teaching and research. She has been authored and/or co-authored various book chapters, international journal papers and review papers on the research in material science. Her area of research interests includes hybrid composites, filled polymer composites, fracture mechanics and structural integrity. Presently, she is supervising Ph.D. student in the fields of nano fibre membrane and 1 Ph.D. and 1 Master’s students graduated under her supervision in 2017–2020. She has several research grants at university and national levels in the various research areas. She is an associate member of the Board of Engineering Malaysia (BEM) and the International Association of Engineering (IAENG).

Structural Health Monitoring of Laminated Materials for Aerospace Application Gérald Franz and Muhammad Hafiz Hassan

1 Introduction 1.1 Composite Materials For many years, pure aluminum was mostly used in the aerospace industry—which could account for up to 70% of an aircraft’s structure weight—because it had the advantage of being lightweight, cheap and readily available [1–3]. The use of conventional aluminum alloys has long been preferred to obtain better stiffness and strength [1], but it has been observed that in the long term, corrosion problems and failures could appear with this kind of materials [4]. Composite materials have gradually replaced the conventional metal alloys in aircraft structures due to their high strength-to-weight ratio, excellent fatigue tolerance and good corrosion resistance [5–7]. Before the 1990s, composites materials were exclusively restricted to secondary structures and represented less than 10% of the airplane whole weight (cf. Fig. 1). Nowadays, laminated materials are used for primary structures on many modern aircrafts, such as Boeing B787 and Airbus A350XWB which the half of their structural weight consists of composite materials [8–10].

G. Franz (B) Laboratoire des Technologies Innovantes, UR UPJV 3899, Avenue des Facultés, Le Bailly, 80025 Amiens, France e-mail: [email protected] M. H. Hassan School of Mechanical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_1

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Fig. 1 Percentages of the composites in military and civilian aircraft structures [11]

Fiber Reinforced Polymers (FRPs) are heterogeneous materials which combine lightweight, stiff but brittle reinforcing fibers (aramid, carbon or glass) bound together by a polymer-matrix (thermoplastic or thermoset). The reinforcing phase contributes to improve the mechanical properties of the laminated composite, while the matrix phase transfers load to inner fibers, protects them from external damages and provides the composite material its high fracture toughness [12, 13]. Figure 2 shows the several types of FRPs used in the fabrication of aircraft components, including Aramid FiberReinforced Polymer (AFRP), Carbon Fiber-Reinforced Polymer (CFRP) and Glass Fiber-Reinforced Polymer (GFRP).

1.2 Damage Modes in Composite Materials The failure in composites is heterogeneous and FRPs typically exhibit many local failures, denoted damages, that gradually develop until the final failure of the material. This stepwise evolution is commonly known as damage accumulation or growth. Damages in composite materials usually initiate at the micro-scale within the matrix and at the fiber/matrix interface. Further expand of the load goes with the growth of the matrix cracks, which leads to the emergence of cracks and delamination at the mesoscopic scale, and finally propagate at the macro-scale until ultimate failure. Therefore damage accumulation in laminated composites implies both intralaminar (e.g. fiber failure or matrix cracking) and interlaminar modes (e.g. delamination or debonding) [15].

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Fig. 2 Components made of FRPs used in Airbus [14]

Consequently, most of these damage modes occur gradually within the composite material itself, making them undetectable by a simple visual inspection of the surface. Unfortunately, they can lead to serious consequences for the overall composite structure and harshly degrade its performance. The failure mechanisms or damage modes in FRPs can be listed according to three distinct categories, as depicted Fig. 3, in accordance with the three aforementioned scales they occur: • Micro-level failure mechanisms (matrix micro-cracking, fiber failure, fiber/matrix debonding) • Meso-level failure mechanisms (matrix transverse cracking, splitting, local delamination) • Macro-level failure mechanisms (delamination). Moreover, damage modes in FRPs are strongly dependent on loading conditions. As illustrated Fig. 4, various stresses act on an aircraft during flight, i.e. bending, tension, compression, shear and torsion. The fiber failure mechanism occurring when the fibers are subjected to a tensile, respectively compressive, load in the fiber direction is known as fiber fracture, respectively fiber buckling. When the load is carried out perpendicular to the fiber direction, the related fiber failure mechanism is denoted as fiber bending. Fiber/matrix debonding corresponds to the separation at the interface between the reinforcing phase and the matrix due to the propagation in the fiber direction of cracks initiated in the matrix [19]. This failure mechanism takes place for in-plane transverse tensile stress, in high interfacial stress concentration zones [20]. This damage mode

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Fig. 3 Schematics of the failure mechanisms in FRPs with circular hole under tensile load [16, 17]

Fig. 4 Main mechanical solicitations of in-service aircrafts [18]

does not represent the main failure mechanism in composites, however it certainly jeopardizes the strength of the affected fibers and their vicinity, which may drive to a breakdown when overloaded [21].

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Matrix-transverse cracking and splitting result to the combination of various micro-scale damages, such as matrix micro-cracking or fiber/matrix debonding. The formation in the matrix of a crack perpendicular to the applied load is termed as matrix-transverse cracking, while if the matrix crack propagates along the loading direction, it is denoted as splitting [16]. The separation of proximate composite plies is known as delamination. This macro-scale damage mechanism is considered as the critical mode of failure because delamination significantly decreases the performance of the structure and thus reduces its lifespan. Delamination is caused by the development of micro-cracks in the matrix, acting as interfacial stress concentrator. It may appear due to residual stresses during manufacturing phase or low to medium impacts during machining or in-service [22]. Furthermore, damages due to local impacts which may happen in-flight can be classified into Barely Visible Impact Damage (BVID) and Visible Impact Damage (VID). BVID are due to low-velocity impact as hailstones collision during take-off and landing flight phases [22]. They induce minor damages to the external surface, which may not be seen with the naked-eye, but can also lead to significant degradation within laminated composites, such as large delamination at every change of ply orientation [23, 24]. Therefore, if these hidden damages are not detected at early stage, the structural integrity could be compromised due to their progressive propagation, leading to safety troubles. In contrary to BVID, VID are defined as impact damages which can be reliably detected by visual examination of the laminate surface.

1.3 Structural Health Monitoring for Composite Materials The Aerospace Industry Steering Committee on Structural Health Monitoring (AISCSHM), composed by an international team of industry and research representatives, defines Structural Health Monitoring (SHM) as “the process of acquiring and analysing data from on-board sensors to evaluate the health of a structure” [25]. In other words, SHM systems purpose to detect, locate, classify and quantify damages in engineering structures at their incipient occurring in order to avert severe structural failure. SHM contributes to enquire about the initiation and growth of the damages, leading to a better knowledge of the in-service structure state, necessary to perform an accurate estimation of the structure remaining lifespan. So, the concept of damage implies a comparison between the undamaged and damaged states, although damages cannot be measured directly. Instead, the structural properties, such as stiffness, strength or impact resistance, are monitored because damages effect on these specific properties and can be correlated to the detection of failure. The SHM scheme proposed by Rytter [26] is decomposed into a diagnosis part, consisting in determining the damage state of the monitored structure, and a prognosis part which the main purpose is to estimate the remaining useful life of this structure. The diagnosis step relies on a sequence of four levels which allow to successively answer regarding to the existence (i.e. detection), the geometrical position (i.e.

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localization), the nature (i.e. classification) and the extent (i.e. quantification) of the damage. The damage diagnosis is achieved thanks to model-based, respectively datadriven, algorithms which compare the measurements acquired by sensors attached or embedded in the monitored structure to the results of analytical or numerical models, respectively to a measurements database for both the damaged and the undamaged structure. The SHM process is concluded with a prognosis step based on statistical analysis and damage models using the results of the previous step of diagnosis. Note that this last step still remains little discussed in the literature for composite structures. The requirement to develop accurate numerical models directly related to specific applications to prognose structural health, while the damage diagnosis can more commonly be applied to various applications, may explain this statement of fact. SHM systems mainly contain networks of sensors permanently integrated within the host composite structures. These non-destructive in situ detection and evaluation devices allow the aeronautical structures integrity to be monitored during their use throughout their lifespan, without disassembling nor human intervention requirements [22, 27]. The incorporation of a SHM strategy therefore enable to meet both the needs of the aerospace industry in terms of safety and economics. Continuous monitoring of instrumented composite structures provides real-time data and involves better knowledge of their health, which improves their operational reliability while optimizing the organization and management of maintenance interventions. Moreover, the alternative of switching from corrective or timescheduled maintenance—often time-and-cost consuming due to devices immobilization requirements and downtime coupled to human intervention over several days—to condition-based maintenance, represents a real economic gain. In contrary to NonDestructive Testing (NDT) processes—e.g. ultrasonic inspection, X-radiography and thermography camera—which the main objective is to detect manufacturing defects of composites, SHM focuses on detecting damages that may happen on composite components of in-service aircrafts. Besides, NDT techniques can only be performed off-line while SHM methods allow both off-line and on-line detection of damages. The development of SHM has been promoted over the past decade by the improvement of computing capacities and the use of lighter and less-energy consuming wireless sensors. Although the aerospace industry represents a driving sector for R&D in this area, other industries, such as energy [28], rail transport [29] or chemical industry and shipbuilding [30] benefit from these advances.

2 SHM Strategies for Composite Materials The damage detection in composite materials has required the development of a wide range of monitoring tools based on sensors using a physical principle derived from the conventional NDT techniques such as vibrations, acoustic emission (AE) or electromechanical impedance (EMI) among others. Depending on the distribution of aircraft components materials (cf. Fig. 2) and the diversity of mechanical solicitations

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acting on the structure (cf. Fig. 4), the associated failure modes will be different. Consequently, it is impossible to propose a single technique in order to accurately find out the occurrence of damage. So, the choice of the SHM strategy is based on the physical mechanism producing the damage and the combination of different SHM methods can be a promising solution to improve assessment accuracy and reliability of damage, as suggested by Kralovec and Schagerl [31]. In the following section, the most popular sensors types used for SHM applications will be first briefly presented and then the main SHM technologies and their characteristics will be reviewed with considering their respective advantages and drawbacks.

2.1 Main Sensor Types for SHM The reliability and capability of SHM systems is conditioned by the choice of sensor technologies. The selection of sensors involves combining a high precision to detect the presence of damage with a low sensitivity to the environmental conditions of the host structure. In addition, the integration of sensors will automatically generate overweight for the overall structure. So, it is necessary to restrict this overage with small, lightweight and space-saving devices [32]. The main sensors commonly integrated or embedded in aeronautic structures and used to determine the structural health of composites thanks to strain, temperature or vibration acquisitions, are resistance strain gauges, Fiber Optic Sensors (FOS) and specially Fiber Bragg Grating (FBG), piezoelectric sensors (PZT or PVDF) and Micro-Electro-Mechanical Systems (MEMS).

2.1.1

Strain Gauges

The resistance strain gauge is a well-known sensor element used to convert mechanical quantities, such as forces, pressure or temperature into a change of the electrical resistance. This kind of device generally consists of a very thin wire looped into a resistance grid, embedded between two thin elastic layers. The aforementioned electrical resistance varies in the same way as the sensor bonded onto the host structure deforms with the material under load. The Wheastone bridge, the Chevron bridge and the four-wire ohm circuit constitute the common signal-processing networks used to convert electrical resistance change to voltage signal. The ratio of electrical resistance’s change by the strain, denoted gauge factor, gives the strain gauge’s sensitivity. For more details about the strain gauge, the reader can refer to the chapter entitled “Mechanical test methods for lamina” of the Staab’s book [33].

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Fiber Optic Sensors (FOS)

Fiber Optic Sensors (FOS), when they are embedded within structural components, allow to monitor structural integrity of the host material by providing accurately the measure of key-parameters such as strain, temperature or vibration. These sensors detect the presence of damage by using the physical properties of light, i.e. optical path length and optical absorption, which are modified by the aforementioned surrounding conditions when the light pass through the optical fiber. Optical fiber can be considered as a waveguide which uses the refractive properties of the light. It commonly consists of a core surrounded by a cladding with a slightly lower refractive index than the core one. The refractive index of a material is a dimensionless ratio used to characterize the propagation velocity of light through the material. Two types of fiber can be distinguished, i.e. plastic-fiber and glass-fiber. The core of plastic-fiber is composed of 0.25–1 mm diameter acrylic-resin fibers while the core of glass-fiber consists of glass fibers with a diameter varying from 10 to 100 µm. Plastic-fibers are found in many FOS applications due to their lightness, cost-effectiveness and flexibility, but for high operating temperature applications, glass-fibers will be preferred to them. FOS are particularly appreciated for SHM applications because these devices only consist of an amplifier and cable, without any additional electronic components, thus allowing to be lightweight, space-saving, unsensitive to electromagnetic interferences, enduring, etc. [34]. Many applications of fiber optic structural sensing can be found in Measures’ book [35].

2.1.3

Fiber Bragg Gratings (FBG)

Amongst a large range of FOS available to evaluate the structural health of the monitored material, Fiber Bragg Gratings (FBG) represent a device widely used in numerous SHM systems, particularly for laminated composites [36–41] and aeronautics applications [42–44]. Contrary to the refractive index of the core in a “classical” optical fiber which remains uniform along the length of the fiber, FBG correspond to a modified refractive index. It is formed by the periodic modulation of this index allowing the reflection of specific wavelengths of light. When an externally applied mechanical or thermal loading occurs on the sensing area by FBG, the reflected wavelength varies proportionally. Knowing the linear relationship between the wavelength variation of the reflected light and the strain in the fiber caused by the external event, it is possible to obtain accurately the value of this modification. Moreover, FBG offer the strong advantage to be multiplexed into large sensors networks, meaning that an only single strand of optical fiber is required to arrange many sensors providing quasi-distributed measurement on the host structure while limiting the impact of the overall weight of the sensing device. In this specific case, it will be necessary to ensure that the different Bragg gratings are associated with

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different wavelengths in order to be able to easily identify them. The reader interested by FBG can refer to [34, 45] for more details concerning the theory, the physical principle known as Fresnel reflection, the methods of fabrication of this kind of sensor and the properties of gratings.

2.1.4

Piezoelectric Sensors (PZT or PVDF)

The structural health can be examined using piezoelectric sensors commonly made in Lead Zirconium Titanate ceramics (LZT or PZT) or PolyVinyliDene Fluoride films (PVDF) due to their lightweight, low cost and small size. These sensors are used for measuring low or high frequency vibrations, which variations reflect the presence of damage. A piezoelectric material subjected to a mechanical loading possess the ability, known as piezoelectric effect, to convert it into an electric charge. Reciprocally, when an external electric field is applied to this kind of material, a strain field is induced; this phenomenon is named inverse piezoelectric effect. This electromechanical coupling property allows the use of piezoelectric sensors both as actuators and receivers [46]. PVDF films offer a credible alternative of PZT ceramics when a curved surface has to be monitored. Indeed, PZT ceramics remain quite brittle while PVDF films exhibit high flexibility, although their electromechanical coupling property is lower than PZT one. As specified by Güemes et al. [22], all the theoretical and experimental information required by practitioners to work with PZT can be found in Giurgiutiu’s book [47].

2.1.5

Micro-electro-mechanical Systems (MEMS)

The permanent requirement to monitor the structural health without overloading the overall aerospace structures led to develop miniaturized sensing technologies such as Micro-Electro-Mechanical Systems (MEMS). MEMS are silicon-based devices which combine miniature mechanical components and micro-electrical circuits. They are obtained by advanced integrated circuit (IC) fabrication methods. In addition to their extremely small size facilitating their integration within the monitored structure, MEMS are cheap, provide high sensing accuracy and low power consumption. In order to preserve the advantage of weight-saving of these micro-sensors when they are used in multi-sensors SHM systems, a wireless communication technology is often preferred to limit cabling. More details on MEMS, their fabrication processes and their integration on SHM systems for aerospace applications can be found in [48–51].

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2.2 SHM Methods 2.2.1

Classification

SHM technologies may be usually decomposed into local and global techniques [52, 53]. The distinction between these two damage identification techniques is relied on the size of the monitored zone. The local methods aggregate the SHM techniques which the inspected area is concentrated on a limited part of the overall structure, located under the sensor. In this way, these methods allow the detection of small damages such as cracks and need to previously know the position of the area prone to damages. When the presence and the position of the damage can be identified on a large zone of the structure, the SHM techniques are qualified as global. In this case, a well-distributed sensors network is attached or embedded in the composite structure. Due to a resolution often more limited than ones of the local methods, the global techniques may only find out more severe damages. Moreover, SHM systems can also be performed with active or passive devices [47, 54, 55]. In active SHM, sensors may be used both as transmitters and receivers, the monitoring structure is stimulated by controlled signals, such as vibration-based methods [56–62], Lamb waves [32, 47, 63–71] and EMI [72–75]. Then the received responses are compared with the measurements of the undamaged structure in order to determine the structural health. The application of active sensing techniques to monitor transverse matrix cracking and estimate the fatigue cracks inside laminated composites is detailed in [76]. Despite a sound capacity to detect damage in structures, active SHM methods cannot be used to perform monitoring of large structural areas. Besides, these techniques are also restrained by the requirement of extensive hardware and power supply. Contrariwise, passive SHM methods, including AE [77–85], strain-based methods [86–92] and Comparative Vacuum Monitoring (CVM) [93–95], lean on the use of sensors acting only as receivers and the measured signal results from external sources as normal in-flight loads or damage events such as bird-strike. In these configurations, less hardware and power supply are necessary compared to active SHM techniques, larger zones can be monitored but an effective locating of damage is more difficult to acquire. An illustration of real-time damage diagnosis for in-service impacts on laminated composite structures provided from integrated passive SHM is given in [76].

2.2.2

Vibration-Based Methods

Vibration-based methods constitute typical active approaches commonly used in SHM applications [56–62]. These methods require to measure the vibration response of the monitored structure, which a change warns the presence of damage. Indeed, the structural dynamic characteristics are linked to the mass, damping or stiffness properties of the material [56, 59], which are effected by damages, arising significant differences in the vibration signature between the undamaged and damaged

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structure. The vibration characteristics, such as natural frequencies, modes shapes or Frequency Response Function (FRF), are commonly measured thanks to accelerometers, piezoelectric sensors or FOS, which make the real-time structural monitoring simple to implement. Although the vibration-based techniques can detect and locate damage thanks to non-model based methods, i.e. studying the variations of the vibrational modes compared to experimental data of the pristine structure, model based methods are often preferred for SHM applications because they can also provide a quantification of these damages. In order to identify and assess damages, the model based methods correlate the results of numerical or analytical models with experimental data from damaged structure. It is been widely assumed that structural behaviour can be modelled with linear equations and related with the structural vibration characteristics, even if it is also well-known that the damage is a non-linear mechanism. This a priori contradiction can be reasonably justified since the structural dynamic characteristics are experimentally found out at low-level vibrations, corresponding to linear measured responses for various damaged structures. Model based damage identification involves determining accurate numerical models to represent mathematically the behaviour of the structure. Finite Element (FE) models are commonly chosen to describe the motion of the system thanks to the mass, damping and stiffness matrices which are modified when damage occurs. The definition of damage indicators is needed to identify damage modes by investigating their variations in the model. The numerical results are correlated with the experimental measurements and model outcomes are updated to minimize difference between calculated and measured values. The convergence of the optimization process of this gap is impacted by the choice of the objective function representing it. Damage is commonly detected using natural frequencies due to their simplicity to measure and their lower sensitivity to the measuring noise, compared to modal damping or mode shapes. The natural frequency of a system corresponds to the frequency of which the system naturally vibrates when it is disturbed. There exist various objective functions based on this damage indicator among them we can cite Cawley-Adams criterion [96], Damage Location Assurance Criterion (DLAC) [97] and its extension to the existence of multiple damage location, denoted Multiple Damage Location Assurance Criterion (MDLAC) [98]. Cawley and Adams were the first to propose detecting damage, restricted to single damage case, by correlating natural frequencies changes for 1D and 2D structures with FE model results [96]. Messina et al. have improved the estimation of size and location of damages with natural frequencies changes by proposing two criteria known as DLAC [97] and MDLAC [98]. Another way to identify damage consists of comparison between experimental and analytical modal vectors. Mode-shape analysis can provide information about damage location since mode-shape changes are sensitively related to damage. In this case, the Modal Assurance Criterion (MAC) can be introduced as a statistical factor expressing the extent correlation of these two mode shapes, ranging from zero (no correlation) to one (fully consistent modes) [99]. Note that the DLAC method

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stands on the same concept as the MAC one, but replacing the study of correlation of the mode shapes by the natural frequencies one [100]. More developed forms of MAC indicator, such as Coordinate MAC (COMAC) [101], can also be computed to evaluate the difference between experimental and numerical modes. The use of the FRF represents an alternative approach to detect and locate damage and various criteria have been proposed, such as Frequency Response Assurance Criterion (FRAC), Frequency Domain Assurance Criterion (FDAC) [102], Global Shape Correlation (GSC) and Global Amplitude Criterion (GAC) [103]. As the MAC indicator, the FRAC factor takes values from zero to one. However, the FRAC allows to correlate the frequency response, including all the individual modes, where the MAC indicator only correlates the individual modes. It is important to remind that vibration-based SHM techniques are global damage detection methods, which cannot accurately determine the type and extent of the damage due to a lower resolution than ones obtained with local techniques. Consequently, these methods are preferentially used to detect large cracks which the vibration responses are significantly impacted regarding the first frequencies or the modal shapes.

2.2.3

Lamb Waves

For decades, Lamb-waves-based damage identification represents an active and global SHM method particularly appreciated for aeronautics applications, which require detecting and assessing along large area both surface and internal damages with very small size. The interest driven by Lamb waves arose from the early 1990s, especially for the detection in composite materials [63], since these waves can propagate without deviating over long distances even in materials with high attenuation ratios such as CFRP. Horace Lamb was the first to discover and provide the fundamentals and basic theory of a kind of guided elastic waves generated in thin plate or shell structures, now called Lamb waves [104]. In practical terms, PZT transducers are used to generate and receive Lamb waves. PZT actuators and sensors can be either attached on the host structure or embedded within it. Although the advances in miniaturization and IC manufacturing processes may encourage the embedment of sensors, thus offering numerous benefits such as high sensitivity to internal damage, excellent insensitivity to ambient noise, outstanding performances in data acquisition, the surface-mounted sensors are often preferred because they remain more appropriate for maintenance or replacement operations due to their easier accessibility. Moreover, it is necessary to respect some precautions to prevent the risk of short-circuit of the embedded sensors during the composite manufacturing process due to high temperature and pressure in autoclaving. The introduction of foreign element within the composite material may also disturb the inter-laminar stress distribution, leading to a weakening of the load-carrying property of the laminated composite.

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Lamb waves are obtained by the resonance of waves in the structure as they reflect off the boundaries. The received signals are stored and compared to recorded signals during the entire structure lifetime. Any structural change on the sensing network path is picked up by a signal distortion. Lamb-waves-based damage identification is specifically adapted to thin laminated structures and quite sensitive to small delamination caused by impact. However, the propagation of Lamb waves is influenced by material properties, thickness and boundaries conditions, which make more challenging the monitoring of real structures with stiffeners, boundaries and thickness variations [22]. Thus, the dispersive nature of the Lamb waves—their propagation velocity is dependent on exciting frequency—complicates the signal acquisition and evaluation of complex structures. Various characteristics parameters reacting to damage occurrence can be derived from Lamb waves signals emitted or received by a transducer or by sensors network. The damage identification approach is therefore based on an inverse analysis since the received signal, transposing the current damage state of the inspected structure, is used to determine the damage location, shape and severity at the origin of the change of the analysed signal. The damage state of the structure is identified by building damage-sensitive features, well-known as Damage Index (DI), obtained from analysis in time, frequency or time–frequency domains of the recorded signals. DI extracted from Lamb waves signal of the monitored structure are compared to a database of DI coming from experimental or numerical signals, which correspond to numerous identified damage states in terms of location, shape and severity. The decrease of the distance between the sensor position and the damage location generate a raise of the DI value. The same tendency is observed when the degree of damage becomes higher. Time-Of-Flight (TOF), signal amplitude (A) and Power Spectral Density (PSD) are signal characteristics, which changes may be correlated to matrix cracking and delamination for laminated composites [105, 106]. TOF represents the required time for an actuated wave to propagate on the distance between a transducer pair. Due to its noticeable sensitivity to delamination, TOF constitutes a popular DI used for Lambwaves-based damage identification of laminated composites. In the case of multiple transducers pairs, the use of a triangulation procedure is necessary to locate damage from the evaluation of the difference relating the DI between the damage-scattered and incident waves extracted from several signals damage [63, 107–110]. The purpose of this section was to provide only a quick overview about damage identification techniques using Lamb waves, interested reader will be able to find further detailed information in [32, 64] concerning fundamentals and mechanisms of activation, propagation and acquisition of Lamb waves in various engineering structures including laminated composites, selection of adapted transducers and sensor networks, digital signal processing or algorithms dedicated to Lamb-waves-based damage identification methods.

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Electro-mechanical Impedance (EMI)

The local mechanical impedance of a structure, expressed as the ratio of the applied force to the resulting velocity, is perturbated by the presence of damages such as delamination or cracks. Thus, it can be used as an indicator to detect a damaged state of the monitored material. In practice, this impedance remains difficult to get, that’s why EMI techniques are based on the local measurement of the mechanical impedance performed indirectly by using the electromechanical coupling effect of a PZT transducer acting simultaneously as actuator and sensor [111]. In this configuration, the host structure is excited by applying a sinusoidal voltage to the PZT transducer (acting as actuator) at high frequencies ranging from a few kHz to hundreds of kHz, while measuring the resulting electrical response with the same PZT transducer (acting as sensor). As firstly shown by Liang et al. [111], the inverse of the electrical impedance, known as the electrical admittance, can be expressed as a function of the mechanical impedance of the attached PZT transducer and that of the monitored structure. Thus, the electrical impedance is directly related to the mechanical impedance of the monitored structure and its variations can be attributed to change of structural integrity. Therefore, EMI methods can be used to assess the severity of the damage by quantifying the level of variations of the electrical impedance signature, thanks to statistics-based damage metrics such as the Root Mean Square Deviation (RMSD), Mean Absolute Percentage Deviation (MAPD), Covariance (Cov), Correlation Coefficient (CC) [47]. All these damage metrics are based on the comparison of the PZT impedance of the structure measured at the considered instant with the reference impedance signature corresponding to the undamaged structure. It was experimentally demonstrated that RMSD and MAPD were more appropriate for locating and evaluating the damage growth while Cov and CC were the relevant statistics-based damage metrics to identify the damage size evolution at a fixed location [112]. However, it was also observed that RMSD and CC damage metrics were highly sensitive to ambient temperature changes, which complicates to differentiate damage from small temperature variation for structure exhibiting tiny delamination and may consequently provoke fake damage diagnosis [113, 114]. Thus, in order to properly detect small damages with EMI method, it is necessary to provide temperature compensation techniques, such as ones proposed in [115–117]. EMI techniques perform the impedance measurement at ultrasonic frequencies range (from few kHz to hundreds of kHz), which allow the detection of small incipient defects, impossible to locate with the vibration-based methods (see Sect. 2.2.2) acting at low frequencies [72]. Moreover, the excitation of high frequencies range for EMI techniques offers the advantage to have a SHM method insensitive to vibrations due to outside environment. More details on the EMI technique are provided in references [73, 118, 119].

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15

Acoustic Emission (AE)

AE is a transient elastic wave caused by a sudden release of local strain energy resulting from microstructural changes such as the sharp occurrence of a crack within a stressed material [11]. AE technique was firstly applied to control the structural integrity of composite materials and structures without deteriorating them during their inspection [78, 80, 120, 121]. It became a well-esteemed passive SHM method thanks to the use of PZT sensors embedded or attached to the surface of the host structure, which allows to capture stress waves generated by external events such as impacts and thus providing fast and inexpensive real-time information on damage initiation and propagation within the monitored material. Fatigue tests performed on unidirectional (UD) and cross-ply GFRP monitored by surface-mounted and embedded PZT sensors were used to investigate the impact of the sensor location on the sensitivity of damage detection and the mechanical properties of the host structure [122]. In this study, it was demonstrated that the embedment of sensors within the GFRP specimen promoted a better detection of the acoustic events compared to a monitoring approach using surface-mounted sensors. Indeed, the UD, respectively cross-ply, GFRP with embedded PZT sensed about ten times, respectively two times, more events than the same GFRP with attached sensors to the surface. Moreover, it was also observed that the embedded sensors did not act as damage initiation sites since the occurrence and growth of damage were remote from these sensors location. AE sensing was proved to be more suitable than other NDT techniques to identify damage modes such as fiber breakage, delamination, matrix micro-cracks or fibermatrix debonding, when stress is applied to a composite material [123]. By the nature of the detected events, the electrical signal provided by the sensor is short burst. The detectability of AE signal is related to its amplitude, which is substantially influenced by the ability of the wave to propagate through the material. The signal duration is impacted by the direct and reflected paths of the stress wave within the material. Thus, although AE is extremely sensitive to the damage occurrence and evolution in composite structure, this SHM technique requires knowing beforehand the velocity and attenuation of wave propagation in the composite material to be fully and soundly exploited to warn on impending failure. This aspect is notably addressed by Ono in his comprehensive review on AE [85] or previously in the works of Mechraoui et al. [124] about the evolution of speed of acoustic waves in composite materials. AE measurements are performed at ultrasonic frequencies ranging from 20 kHz to 1 MHz to detect the incipient occurrence of failure in composite structures. Beyond these frequencies, the AE signal amplitude becomes too low. Damage detection is realized after signal processing to extract the AE signal parameters, such as amplitude, duration or rise time, useful to analysis. As shown on Fig. 5, the amplitude corresponds to the highest peak value of the AE signal, the duration gives the time interval between the first and the last instant the pulse crosses the threshold, and the rise time is the period between the first threshold crossing and the highest peak of

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Fig. 5 Main parameters of an AE signal [125]

the AE signal. AE source location, corresponding to damage location, can also be determined using the time information of the AE signal.

2.2.6

Strain-Based Methods

It is well-known that the presence of damage alters the local strain distribution and/or magnitude of a structure subjected to normal operational loads. Therefore, strainbased approach constitutes a passive SHM method more effective to detect damage in local structural hotspots than in the overall structure [126, 127]. The strain-based SHM dedicated to aircraft structures were mostly studied in laboratory with simulated operational environment. However, some research works have been performed under in-flight condition and the distributed strains were measured thanks to strain gauges and FOS [128, 129]. More generally, strain-based systems use sensors such as strain gauges, FOS, FBG and PZT transducers to monitor the distributed strains. Damage detection can be performed by comparison of the current strain distribution with the one of the pristine structure or with theoretical model. Several studies have shown that the analysis of strain measurements obtained by FBG in CFRP was suitable to detect delamination and impact damages for these laminated composites [130–132]. Recently, Grassia et al. have shown promising laboratory tests results concerning the possibility to locate structural damages by evaluating the difference between the distributed strain measured by strain gauges in carbon/epoxy material and the strains predicted by Annotatable Neural Network (ANN), with the perspective to applied

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this SHM approach on aeronautical structure since numerous strain gauges can be replaced by FBG to provide a distributed strain measure with a lightweight device [133]. Alvarez-Montoya et al. developed a strain-based SHM system including 20 FBG embedded into the wing’s front spar made of composite, which demonstrated its ability to perform strain monitoring during flight tests in operating condition, without loss data. The in-flight data were used to validate a previously developed damage detection methodology based on machine learning algorithms in conjunction with damage indices used for classification [134].

2.2.7

Comparative Vacuum Monitoring (CVM™)

CVM™ is a simple and mature passive SHM method developed by Structural Monitoring Systems Ltd for applications in the aerospace industry. This pneumatic technology was first used to detect crack initiation and propagation in metallic structures, and further extended to the monitoring of BVID and delamination for composite structures [135]. The functionality, durability, robustness and accuracy of this technique were demonstrated through numerous laboratory-based and in-service aircraft programs [136]. CVM™ method is based on the elementary principle that a vacuum maintained within a small volume is extremely sensitive to leakage [93]. The CVM™ device consists of a sensor bonded to the surface of the host structure and connected to a stable source of low vacuum and a sensitive fluid flow meter. The CVM™ sensor relates to fine separated alternating air (at ambient pressure) and vacuum galleries, which are open to the monitored surface. The flow meter measures the pressure differential between the reference vacuum source and the sensor. Initially, with the absence of any defect, this differential equals 0 Pa. The occurrence and growth of damages generate a breakage path between the alternated galleries, allowing the air circulation from the air channels to the vacuum ones. Consequently, that leads to a pressure rising which the magnitude can be related to the overall damage severity [94]. The minimal crack size which can be detected by CVM™ sensor directly depends on the gallery spacing. In the case of laminated composites, the CVM™ galleries can be inserted at the interlaminar scale from the manufacturing stage of the material. The influence of the geometrical characteristics of CVM™ galleries, such as diameter, cross-sectional shape, size and orientation, on interlaminar [137, 138], in-plane tensile and compressive [139] performances of carbon/epoxy laminates have been studied in order to evaluate the structural consequences of the inclusion of CVM™ sensors which can limit the use of this technique. The tensile and compressive moduli are affected by the channel diameter and the degradation of the elastic properties, as well as the one of tensile and compressive strengths, is softened when the galleries are aligned with the load direction. Moreover, whatever the cross-sectional shape of the gallery, i.e.

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circular or elliptical, the mode I (normal tensile stress) interlaminar fracture toughness is improved when galleries are perpendicular to the direction of the crack growth. The increase of the gallery diameter up to a critical size also leads to an improvement of the mode I delamination while the mode II (interlaminar shear stress) interlaminar fracture resistance decreases. Thus, the use of thin galleries aligned with the load direction is preconized for the CVM™-monitored composite aircraft structures in order to alleviate the loss of structural performance.

3 Conclusion SHM systems are required to ensure the structural integrity of composite aircraft components which are exposed to various loadings and impact events during the flight. These phenomena related to tough environmental conditions in-use may lead to damage such as matrix crack, fiber breakage or delamination which remain undetectable by visual inspection. If these invisible damages are not detected at early stage, the structural integrity can be critically degraded due to their progressive propagation. The achievement of a SHM strategy is part of an interconnected multidisciplinary framework based on the mechanical and geometrical properties of the monitored structure, considered damage modes, damage detection and location methods and sensing technologies. In particular, the damage diagnosis scheme depends on the choice of SHM techniques coupled with the selection of the embedded or surfacemounted sensing technologies of the monitored composite structures. SHM technologies can be distinguished regarding to the extent of the monitored area and the way to detect damage. The inspection of large zone of the structure implies to find out more severe damages while the monitoring of restricted area allows the detection of smallest damages. Furthermore, active damage detection is performed by injecting diagnosis signals into composite structure and analysing the received response, while passive damage detection only requires to measure signal resulting from external events. This chapter endeavored to provide the strengths and weaknesses of main monitoring methods in order to discriminate the ones that allow to accurately identify the size and the locating of damage as a function of the selected damage scenario and the type of host structure. Due to the specific aspects of each SHM technique concerning the type and extent of detected damages, summarized in Table 1, it can be judicious to combine several SHM methods to improve assessment accuracy and reliability of damage.

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Table 1 Summary of SHM methods SHM method

Actuation approach

Detection area

Detectable damage modes

Sensor

Ritter scale

Vibration-based methods

Active

Global

Debonding Delamination Crack

PZT FOS

Levels 1–4

Lamb waves

Active

Global

Impact Debonding Delamination Crack

PZT FOS, FBG

Levels 1 and 2

EMI

Active

Local

Debonding Delamination Crack

PZT

Levels 1–3

AE

Passive

Global

Impact Delamination Crack

PZT

Levels 1, 2 and 4

Strain-based methods

Passive

Local

Impact Debonding Delamination Crack

Strain gauge PZT FOS, FBG

Levels 1–3

CVM

Passive

Local

Debonding Delamination Crack

PZT

Levels 1–4

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Modeling of Damage Evaluation and Failure of Laminated Composite Materials J. Joy Mathavan, Muhammad Hafiz Hassan, and Gérald Franz

1 Introduction Due to the anisotropy and heterogeneity of fiber-reinforced composite materials, the growth of damage in the composite materials is a complicated process. In contrast to metallic materials, damage to fiber-reinforced composites under static or cyclic loading situations [1] with very large amplitudes is dispersed rather than confined [2]. The damage-accumulation process, which is associated with the beginning and progression of a damage, frequently causes composite materials to lose some of their elastic properties, known as stiffness degradation. In reality, the change in stiffness during the fatigue life of a fibre composite material caused by change in residual strength is normally lesser than the degradation [3]. Additionally, since the development of microdefects always occurs before the formation of macrocracks, the spread of a single macrocrack in the structure does not always cause for the failure in a composite [4]. Various microdamage mechanisms begun based on the level of anisotropy, inhomogeneity, and the loading conditions used. They can manifest and grow individually or in combination, resulting in a range of situations for the failure of composite materials or for the degradation of their properties [5]. Additionally, the causes of failure of composite materials and degradation of properties are dependent J. J. Mathavan Department of Engineering Technology, Faculty of Technology, University of Jaffna, Kilinochchi Premises, Arviyal Nagar 44000, Sri Lanka J. J. Mathavan · M. H. Hassan (B) School of Mechanical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia e-mail: [email protected] G. Franz Laboratoire des Technologies Innovantes, UR UPJV 3899, Avenue des Facultés, Le Bailly, 80025 Amiens, France © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_2

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on the scaling factors of the composite structure. As a result, multiscale modelling of the damage accumulation process in relation to the deterioration of the property is required [6, 7].

2 Microdefect Mechanisms in Fiber-Reinforced Composites In this part, the outline of several common microdefect mechanisms that occur during the formation and accumulation of microdefects in fiber-reinforced composite laminates will be discovered. Instead of providing a detailed analysis of the damageaccumulation procedure that directs to the failure of microdamage mechanisms at the ply and constituent scales of fibre reinforced composite materials subjected to variance of loading, the goal here is to highlight the distinct and key damage mechanisms that causes the degradation of properties in composite materials [8, 9].

2.1 Typical Microdefect Mechanisms During manufacturing, some microdefects, called “built-in defects,” are easy to see. These include broken fibres, volumetric voids in the matrix, misaligned fibres, and disbonds at fibre matrix interfaces. Disbonds are areas where the fibres and matrix no longer stick together. Although these mechanisms are quite tiny and thus unlikely to cause the composite to fail entirely, they can gradually deteriorate its effective qualities. Similarly, voids in composite materials can impair their mechanical qualities [10]. When initial loads are applied to composites, these broken fibres, voids and disbonds can also operate as stress risers, collecting and/or triggering additional microdamage environments. As a result, these degradation processes can have a vital effect on the failure of fibre composite materials and deformation behavior depending on their size, shape, and distribution [11]. Since composites aren’t uniform, damage starts to spread or change in fiberreinforced composite materials early in the loading process, which includes mismatched fibre, matrix, and interface properties. Anisotropy (which includes the directional properties of fibres and the orientation of a fibre in the laminate) and matrices such as transversely isotropic and isotropic are also some causes for damage propagation early in the loading process. Because of these properties of composites, whenever external loads are applied, significant inhomogeneous stress and strain fields arise. Stress inhomogeneity is exacerbated further in composites by geometricscale structural characteristics namely ply thickness, fibre volume fraction, layup number and localized fibre packing and spacing [12]. In addition, the stress inhomogeneity of composites may be exacerbated by inherent flaws [13]. Thus, some microvolumes in the composite are likely to experience higher levels of localized stress than others, which can lead to a variety of damage, including new types of damage, and the expansion of existing damage, if the higher localized stresses exceed their respective

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strength limits at an early loading stage. This damage-accumulation process results in a rise in stress redistribution and stress inhomogeneity in the composite, as a result of the increasing size and presence of microdefects, which are the consequence of the increased number of loading cycles in fatigue loading or increased load in quasistatic loading [9, 13]. In return, when the number of loading cycles or size of the load increases, the effective characteristics of a fibre composite material change or decrease. Some micro damages may reach saturation points in the middle and end stages of loading or combined, resulting in the formation of further microdamage mechanisms and the appearance of macrocracks, which may ultimately result in the failure of the fibre reinforced composite material [14]. Our primary focus is on the microdamage mechanisms that start and develop during the initial and intermediate loading steps for composite materials (see Fig. 1). Apart from the inhomogeneity and anisotropy of a composite, microdamage mechanisms are triggered by the loading circumstances that were used on the composite material. Individual fibres fail at their weakest points when a unidirectional fibre reinforced composite is exposed to quasistatic or cyclic tensile loading along the fibres because the fibres carry practically all of the load. These weak areas may be defined by built-in problems within and adjacent to the fibers or by flaws in the fiber architecture. Fiber breaking is the predominant mechanism of fracture during the initial loading process since it regulates the growth and accumulation of local microdamage leading to the composite’s ultimate failure. This is because when a fiber breaks, it perturbs the local tension in its surroundings, resulting in stress rearrangement between the fibers and the matrix. Zero stress exists where the fibre breaks, and some distance away from the break is referred to as an ineffective length when

Fig. 1 Classification of microdefects in composite materials and a few significant microdefects

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tension is progressively recovered. The fibre matrix interface and matrix also redistribute stress to neighboring fibres, creating an area of elevated stress concentrated near broken fibres and causing further fibre breakage provided that the strength limit of the fiber is exceeded. Additionally, this area of high concentration is expected to induce extra microdamage mechanisms in the matrix and at the interface [15]. These mechanisms include longitudinal microcracks (cracks along the fiber) and transverse microcracks (cracks to the fiber). A transverse microcrack in the matrix may grow to reach neighboring fibres when it begins at the ends of shattered fibres and spreads outward [15]. From the ends of fractured fibers, a transverse microcrack in the matrix might expand to reach adjoining fibers. If the break spreads over nearby fibres, a fiber-bridge crack is thought to form at this point. Additionally, the fracture may be stopped at the intersections of nearby fibres that are still intact, leading to the formation of longitudinal microcracks. A longitudinal microcrack that is started by a broken fibre might spread in the matrix or at the fiber-matrix interface, a process called as debonding. Damage progression situations are dependent on interfacial adhesion strength, underscoring the interface’s critical involvement in the microdamage mechanisms of the fiber reinforced composite materials. If the interface is robust, transverse matrix microcracks will develop and spread, whereas longitudinal or axial matrix microcracks will form and grow if the interface is relatively weak [13]. For multidirectional laminates exposed to fatigue tensile and quasistatic loading circumstances, the longitudinal or axial plies continue to be crucial structural components that withstand applied loads and retain the functionality of the composite structure. The laminate’s symmetric off-axis and transverse plies, as well as the order in which these plies are stacked, can have a big impact on how well the longitudinal layers of the composite perform; that is, the rate at which microdamage mechanisms initiate and accumulate on off-axis and transverse plies which can affect the inhomogeneous stress distributions of longitudinal layers adversely, and thus influence the performance. Assume quasistatic tensile or fatigue loading causes normal damage to cross-ply laminates. Disbonds and matrix microcracks in transverse plies might occur during initial loading. Debonding microdamage is more common in transverse plies due to the greater strength of the fiber and matrix compared to the interface. Stress risers are formed by unbroken fibers near disbonds, and matrix microcracks begin to emerge because of continued loading. These disbonds merge to generate cracks that cross the transverse ply’s thickness. Plies can develop a succession of numerous transverse-ply cracks in their respective orientations. When transverse-ply fractures emerges, high concentration zones are formed between axial and transverse plies, which may lead to delamination or interlaminar cracking, commonly known as plyseparation microdamage [16, 17]. When fiber reinforced composites are subjected to tensile, tension, compression fatigue stress and compressive loading, delamination can have a significant impact on their performance and integrity. It is also possible for composite structures to delaminate at the margins [18]. Although microcracks begin at a higher applied axial strain in off-axis plies than in transverse plies, damage evolution is similar as like in quasi-isotropic laminates when off-axis plies are present in the laminate. Off-axis plies can also develop curved or oblique microcracks. There

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are several factors that can affect the onset of and accumulation of microcracks in composite materials, which can have a substantial impact on their properties and failure [19]. It is well acknowledged that fiber micro buckling/kink-band development is the primary cause of longitudinal plies failure under compressive quasistatic and fatigue loads. When a composite is loaded more and more, the fibers shatter at two locations, an event that is frequently triggered by inherent faults such as misalignment of fiber. The kinking process then happens abruptly, which may result in the fiber composite material failing catastrophically. The transfer of stress around the damaged fibre results in the creation of other types of defects. With increased loading, disbonds at the fiber-matrix interfaces, microcracks in the matrix, and delamination between plies may appear. In order to prevent catastrophic failure of fibre composite materials subjected to compressive pressure, interactions between various damage mechanisms are essential. It has been hypothesized that ply splitting, instead of fibre micro buckling, causes kink-band formation, but because of the brief period of the kinking process, the actual mechanism which causes kink-band development is still remain as a question [4, 19]. At the very least at the microscopic level, and predominantly at the constituent level, it is yet unknown how microdamage mechanisms that directs to catastrophic failure emerge, evolve, and interact. This holds true for laminates that are both multidirectional and unidirectional and that are subjected to quasistatic, fatigue compressive, tensile, compressive and multiaxial fatigue loading conditions. However, these stress circumstances are highly destructive to fiber reinforced composite materials, and it is not fully understood how their underlying microdamage mechanisms originate and accumulate, specifically at the constituent level. Based on published data, the numerous significant microdefect classifications, as well as a few significant microdefect classifications, that have been identified in composite materials under a variety of loading circumstances was proposed [20].

2.2 Micromechanical Model of the Composite Materials Degradation Process As previously stated, it is a significant task to predict the damage accumulation process and stiffness deterioration when a variety of factors may have impact on numerous leading damage mechanisms that begin and develop in fibre reinforced composite materials. The majority of industrial researchers and practitioners have opted for an empirical method due to this complexity and difficulties. Although this approach is useful since it uses an empirical mathematical model that has been fitted to real data, it can be rather expensive given the number of experimental programs. Beyond the confines of experimental restrictions, prediction capacity could also be limited. On the other hand, if the underlying physical mechanisms of the composite damage-accumulation procedure are understood, a more tenable mechanism-based approach offers stronger prediction power [21, 22]. It is challenging, as previously

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said, to address all physical causes, especially given the vast array of composite material characteristics, such as stacking sequences, constituent quality, ply directions and other intricate designs and geometries. Instead, one may concentrate on the underlying damage mechanisms that control damage processes when particular loading conditions are applied to composite structures, create their connections with continuum micromechanical models and then improve the models using empirical data [23, 24].

3 Modelling Microdefect Evaluation and Failure in Composite Material Lamina 3.1 Characteristic of Microdefect in Kinetic Model Microparameter si can be used to describe some of the properties of microdefects. Matrix delamination (debonding) from fiber, microcrack length or area, volume of micropores and length or squared length of a crack between layers are all examples of this characteristic. This microparameter can be more accurately described by the relationship between the stress intensity at the fracture tip and the actual stress value in a lamina. Measures of microparameters si are introduced for different sorts of microdefects. These may be scalars, vectors, or tensors. There are several vectors that can be used to describe flat microdefects; for example, a vector that is identical in length, in magnitude and in direction to a normal vector that is defined in the specific coordinate system of a composite construction. Microdefects are often measured using a scalar scale. Another property of these microparameters is that they should not change with the translation of a coordinate system that denotes linear elements of space–time si . A mathematical operation like summing, subtraction, or multiplication will yield the identical values irrespective of the coordinate system employed to measure these parameters [25, 26].

3.2 Kinetic Damage Model A general damage characteristic S will be established, which will be outlined as the total number of microdefects si available in the representative volume element at a particular time in the damage process. Additionally, we will investigate how property degradation is affected by this damage value. The value s varies during the loading process for various sorts of microdefects and it depends on the process parameter t as well as the parameter value t0 , which represents the moment the microcrack started. As a result,

Modeling of Damage Evaluation and Failure of Laminated Composite …

s = s(t, t0 )

33

(1)

The value v that represents the birth rate of microdefects indicates the birth (beginning) of microdefects in the current representative volume of a material (t, S). Say the number of microcracks in a lamina is N. We apply the following formula to determine the quantity of microdefects started during the brief time span dt 0: d N = v(to , S)dto

(2)

Equations (1) and (2) can be used to calculate the total damage based on the quantity of microdefects that were initiated between the times dt0 and t: d S(t, t0 ) = s(t, t0 )v(t, S)dto

(3)

Consequently, the measurement of damage brought on by the appearance of microdefects at various intervals can be expressed as: t S=

s(t, t0 )v(t0 , S)dto

(4)

0

Here, the Volterra integral evolution equation is satisfied by the parameter S presented in Eq. (4), which defines the overall state of damage. Next, we will use the following differential function to define the growth or development process of microdefects: ds = f (t, s, S) dt

(5)

Combining Eqs. (3) and (4), we have dS = s(t, t)v(t, S) + dt

t f (t, s(t, t0 )v(S, t0 )dto

(6)

0

After that, we will use the first two terms of the small-parameter Taylor expansion to extend the function f(t, s, S) in Eq. (4). Lastly, using Eqs. (3), (5), and (6), we get the set of kinetic equations below, which describes the entire damage buildup process: dN = v(t, S); dt

ds ≈ a(t, S) + b(t, S) dt

dS ≈ s0 v(t, S) + b(t, S)S + a(t, S)N dt

(7) (8)

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Here, the scalar microparameters a(t, S) and b(t, S) are associated with the development of microdefects. Lastly, the beginning conditions listed below must be met by the system of kinetic equations presented in Eq. (7): S|t=0 = S0, s|t=0 = s0, v|t=0 = v0,

(9)

The system of kinetic equations produced can be expanded to include situations in which tensor parameters serve to describe both local microdefects and overall damage.

3.3 Damage Evaluation and Failure Process in Lamina The current work thoroughly examines the delamination propagation, failure behaviors and buckling response of a simplified multi-layered fiber reinforced composite laminate with a centrally inserted circular delamination [25, 27]. The laminate is rectangular and has the dimensions L × B × H, as shown in Fig. 2a. The laminate is tested for uniaxial compression force exerted in the x-direction. Only the out-ofplane displacements of the unloaded edges are supported and the loading edges are clamped. The Base-laminate, which is a portion of the entire laminate except for the delaminated area (which is an orifice plate), the Upper sub-laminate, which is in the delamination area and over the delamination location, and the Lower sub-laminate, which is in the delamination area and under the delamination location, are the three components of the delamination boundary and position, as shown in Fig. 2b. According to the theory of brittle fracture mechanics, once the energy release rate at the delamination tip has surpassed a critical threshold, which is G > GC , the delamination will spread. Regarding the current problem under investigation, the

Fig. 2 A composite laminate with an embedded delamination as modelled geometrically and mathematically [28]

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energy release can be stated as the partial differentiation of the total potential energy of the structure with regard to the delamination area (A), as shown below: G=

∂π ∂A

(10)

The boundary conditions and delamination are symmetric about both the x and y axes when the problem under investigation is taken into account. Butler et al. [29] claimed that the delamination has an elliptical form and may be expected to spread only on transverse direction to the compression applied and in our case this is along the y-axis. The dimension parameter r (which is constant before the spread of the delamination i.e., r0 ) can then be used to calculate the area of the propagation of delamination, as shown in Fig. 2a: A = πr0 r

(11)

Then the continuously spreading delamination boundary shape function f D (x, y) in Fig. 2 can be given as: f D (x, y) =

y2 x2 + −1 ro2 r2

(12)

The energy release rate at the transverse delamination tips can be calculated by substituting Eq. (11) into Eq. (10), and the following criteria can be obtained to determine the delamination growth in that particular direction: G=−

1 ∂π ≥ GC πr0 ∂r

(13)

Another important consideration is the selection of GC , which can directly influence how conservative the results were. According to the Benzeggagh-Kenane law, the main mixed-mode state in which delamination propagates is one where there is an opening mode, shearing mode and tearing mode. In addition, as shown in Eq. (13), the critical energy release rate Gc must satisfy the formula GIC < GC < GIIC where GIC , GIIC , and GIIIC are the critical energy release rate components for the three delamination modes, respectively and y is a parameter that has been experimentally fitted to the material. The analytical model discussed above, however, does not allow for the precise determination of Ge and the mixing ratio. Obviously, if G = GIC is assumed, a conservative solution can be found. However, the out-of-plane deflection, which is directly connected to the opening mode, is rather minor for a laminate with limitations on the unloaded edges, and the delamination would primarily occur under a shearing or tearing mode in this scenario. As a result, the critical energy release rate is set at G = GIC , which is more in line with the actual circumstances of this problem. The impact of G on the outcomes will be covered in the following section. Here GI , GII , and GIII are the energy release rate components.

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⎧  n ⎨ G IC + (G IIC − G IC ) G II = GC n  G I +G II G II ⎩ G IC + (G IIC − G IC ) = GC G I +G II +G III

(14)

Additionally, it is found that, for a particular deformation condition, the external force would decrease as the delamination spread farther. The laminate in this work fails when Eq. (15) is satisfied as advised in engineering practice, which occurs after the force has decreased by more than 4.10%. At that point, the calculating process is completed. P < −4.10% Pmax

(15)

Equation (15) offers a way for predicting the residual strength of a delaminated laminate for a specific GC . Furthermore, taking into account the selection of GC inside G IC ≤ G C ≤ G IIC in Eq. (13), the proposed model can then be used to determine a specific failure load range. PI ≤ Pmax ≤ PII

(16)

4 Conclusion The damage development and degradation models presented in this chapter use a micromechanical empirical approach. The formation and degradation of micro defects during the intermediate and final phases of damage development in fiberreinforced composite materials is the main focus of many authors’ works, despite the fact that numerous similar models for describing damage progression in composite materials have been produced. The early and intermediate phases of the damage development process, which are the main subject of the chapter, serve as the framework for the suggested model. As a result, both the micro defect beginning and propagation processes in fiber reinforced composite materials are included in the damage growth and stiffness degradation models. Additionally, the recommended models are strong enough to account for the variety of micro flaws that are generally acknowledged as the main damage processes in charge of deteriorating the useful properties of fibre reinforced composite materials under varied loading conditions. As previously stated, because of the anisotropy and heterogeneity of fiberreinforced composite materials, damage evolution is a highly complicated process. However, modeling and predicting the damage-growth process and its effect on the effective properties of fiber reinforced composites can be simplified by identifying the most likely damaging mechanisms which can cause stiffness degradation. Additionally, using microdamage accumulation and degradation models (for a single ply or multiple plies) which are expected to result stiffness degradation in the laminate

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structure of composite materials, it is simple to assess the degradation of properties that may establish the fatigue limit of any composite material structure, such as stacking sequence and ply orientation. Though, an empirical model is considered to assure the results’ trustworthiness and accuracy to the given experimental data. These suggested models enable to forecast the stiffness degradation of fiber reinforced composite materials with a variety of designs, hence enabling them to anticipate the performance of fiber-reinforced composite materials that are not subjected to experimental limitations.

References 1. Mathavan JJ, Patnaik A (2020) Analysis of wear properties of granite dust filled polymer composite for wind turbine blade. Results Mater 5:100073. https://doi.org/10.1016/j.rinma. 2020.100073 2. Akbari Shahkhosravi N, Yousefi J, Ahmadi Najfabadi M, Minak G, Hosseini-Toudeshky H, Sheibanian F (2019) Static strength and damage evaluation of high speed drilled composite material using acoustic emission and finite element techniques. Eng Fract Mech 210:470–485. https://doi.org/10.1016/j.engfracmech.2018.04.020 3. Akhil MG et al (2021) Metal fiber reinforced composites. Fiber Reinf Compos 479–513. https:// doi.org/10.1016/B978-0-12-821090-1.00024-7 4. Arif MF, Saintier N, Meraghni F, Fitoussi J, Chemisky Y, Robert G (2014) Multiscale fatigue damage characterization in short glass fiber reinforced polyamide-66. Compos Part B Eng 61:55–65. https://doi.org/10.1016/J.COMPOSITESB.2014.01.019 5. Carraro PA, Quaresimin M (2018) Fatigue damage and stiffness evolution in composite laminates: a damage-based framework. Procedia Eng 213:17–24. https://doi.org/10.1016/J.PRO ENG.2018.02.003 6. Cui H, Thomson D, Eskandari S, Petrinic N (2019) A critical study on impact damage simulation of IM7/8552 composite laminate plate. Int J Impact Eng 127:100–109. https://doi.org/10.1016/ j.ijimpeng.2019.01.009 7. Deliktas B, Voyiadjis GZ, Palazotto AN (2009) Simulation of perforation and penetration in metal matrix composite materials using coupled viscoplastic damage model. Compos Part B Eng 40(6):434–442. https://doi.org/10.1016/j.compositesb.2009.04.019 8. Deng J, Xue P, Zhi Yin Q, Jian Lu T, Wei Wang X (2022) A three-dimensional damage analysis framework for fiber-reinforced composite laminates. Compos Struct 115313. https://doi.org/ 10.1016/J.COMPSTRUCT.2022.115313 9. Gholami P, Farsi MA, Kouchakzadeh MA (2021) Stochastic fatigue life prediction of Fiberreinforced laminated composites by continuum damage mechanics-based damage plastic model. Int J Fatigue 152:106456. https://doi.org/10.1016/J.IJFATIGUE.2021.106456 10. Joy Mathavan J, Patnaik A (2020) Development and characterization of polyamide fiber composite filled with fly ash for wind turbine blade. Emerg Trends Mech Eng 131–139 11. Guo G, Alam S, Peel LD (2022) An investigation of deformation and failure mechanisms of fiber-reinforced composites in layered composite armor. Compos Struct 281:115125. https:// doi.org/10.1016/J.COMPSTRUCT.2021.115125 12. Iarve EV, Hoos K, Braginsky M, Zhou E, Mollenhauer DH (2017) Progressive failure simulation in laminated composites under fatigue loading by using discrete damage modeling. J Compos Mater 51(15):2143–2161. https://doi.org/10.1177/0021998316681831 13. Iarve EV, Hoos KH, Nikishkov Y, Makeev A (2018) Discrete damage modeling of static bearing failure in laminated composites. Compos Part A Appl Sci Manuf 108:30–40. https://doi.org/ 10.1016/j.compositesa.2018.02.019

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Damage Detection of Impact-Induced Fiber Glass Laminated Composite (FGLC) Plates Via ANN Approach M. F. Mahmod, Elmi Abu Bakar, and A. R. Othman

1 Introduction Fiberglass pre-impregnated laminated composites (FGLC) have great advantages as compared to the hand lay-up laminated technique in terms of the strength capabilities, minimized the excess resin issues, and reduced the defects from the resinrich problems. Also, FGCL shortens the curing time and process [1]. The damage that commonly occurred during the hand lay-up process such as delamination, fiber breakage, and internal crack can be reduced [2]. Three main factors of the presence of delamination in FGCL is due to air trap during the hand lay-up process, foreign material during the stacking process, and in-service damage. However, the damage caused by the external force is commonly found in in-service damage such as a tool accidentally drops during maintenance service [3]. The damage caused by lowvelocity impact (LVI) in the range of 1–10 m/s affects the strength and stiffness of the FGCL and could lead to catastrophic failure [2, 4]. Since detection the delamination cannot be inspected using naked eyes, several researchers have improved the robust technique to detect delamination for laminated composites. One of the successful M. F. Mahmod (B) Faculty of Mechanical Engineering and Manufacturing, Universiti Tun Hussein Onn Malaysia, Parit Raja, 86400 Batu Pahat, Johor, Malaysia e-mail: [email protected] Structural Integrity and Monitoring Research Group, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, Parit Raja, 86400 Batu Pahat, Johor, Malaysia E. A. Bakar School of Aerospace Engineering, Universiti Sains Malaysia, Nibong Tebal, 14300 Pulau Pinang, Seberang Perai Selatan, Malaysia A. R. Othman Mechanical Engineering Department, University Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_3

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techniques used an advanced computer-based vision system to investigate the effect of temperature on the IID area in hybrid laminated composites [5] and pyramidal truss core sandwiches [6]. However, these proposed techniques are not suitable for working parts. Alternatively, static and dynamic force response-based techniques are introduced using a piezoelectric (PZT) sensor to determine the micro-strain [7] and modal characteristic of delamination growth [2]. Besides, an advanced sensor namely the fiber-Bragg-grating sensing system (FBG) been developed to detect the delamination in laminated composites [8, 9]. However, this technique requires complex wiring installation during the data acquisition process. Another technique used to detect delamination in laminated composites is called the laser Doppler vibrometry (LDV) technique [10, 11] whereas the vibration is measured on the targeted surface and able to determine the location and size of the delamination but limited to the thin sample used only. Thus, ultrasonic testing (UT) is used to detect delamination caused by various types of indenter shapes in thin carbon fiber reinforced plastic (CFRP) material [12]. However, the obtained image was slightly poor, and difficult to identify the delamination size. Besides, UT C-scan image is used to identify the LDV in a thick CFRP sample [13]. Based on the above literature, it can be noticed that the previous research focuses on CFRP application, not FGCL instead. One of the previous studies related to FGCL used was found to determine delamination [14] but the UT scanned image was unable to identify the delamination precisely due to the limitation of equipment capability. Another research was found to use FGCL to characterize the mechanical damage using a tensile test through UT scanned image [15]. There are a few works related to the classification of IID in FGCL using the artificial neural network (ANN) approach [16, 17] but their method is based on the static and dynamic response of the material whereas the input signal is strain and contact force data from PZT and strain gauges sensors. Thus, the detection of IID in FGLC type 7781 E-Glass fabric plates is conducted. An impact test from 0.5 to 3.0 m in height has been applied to the 6 mm thickness of FGLC plates before it immersed in the water tank. The UT scanning process used a 5 MHz transducer and the signal features are extracted using various mother wavelets. Finally, the delamination classification based on an impact force and signal features is performed using the ANN approach.

1.1 Problem Statement Although a lot of the detection of delamination induced by impact in laminated composite has been developed in the last few years, the majority of the detection tends to apply static and dynamic load responses which required the piezoelectric sensor to be attached to the surface of the test specimen. This technique is able to identify the damage behaviour between delamination and impact. However, the epoxy used to attach the sensor on the test specimen surface will leave a footprint and be difficult to eliminate after the sensor has been removed. One of the techniques that will prevent the sensor to contact the test specimen surface is by using ultrasonic

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testing. This method applied sound energy, which is called pulse emitted from the piezoelectric transducer to the surface, and analyzed the received echo to characterize the test specimen. The acquired A-scan signal pattern will differ as the internal damage occurs in the test specimen. Various studies have been made on detecting IID using ultrasonic testing technique [18, 19]. However, all of them used carbon fiber reinforced polymer (CFRP) in their studies, and the compressive strength and mechanical properties were different from FGLC [20]. Previous studies related to fiberglass-based material were done by [14] to investigate the damage after impact. Since the material used is fiberglass-aluminum laminates which are higher ductility, the damage can be visually observed. The work presented also focused more on the empirical relationship during impacts such as maximum contact force and residual displacement. Although [15] have investigated the mechanical damage of fiberglass laminated composites using ultrasonic scanning images, the characterization result is based on tensile which is different from impact-induced delamination studies. Junliang et al. [21] investigated the forced delamination of glass fiber-reinforced polymer (GFRP) based on the thickness and density measurement from the ultrasonic scanned image but did not correlate with impact energy. Based on the previous studies, it was found that the detection of impact-induced delamination was stopped until the detection of the delamination but no attempt was made to classify the delamination against the impact energy. By classifying the delamination against the impact energy, the prediction of delamination behaviour can be made through an impact. This effort is also beneficial during the pre-inspection stage to help the inspector to analyze the internal damage of FGLC and this has motivated the present study.

2 Methodology 2.1 Low Velocity Impact-Induced Delamination Test The low-velocity impact (LVI) test was conducted to investigate the impact-induced delamination (IID) in FGLC plates. Besides, these experiments are provided a better understanding of the relationship between impact energy and visibly surface impact damage before the delamination behaviour of FGLC can be identified. In general, LVI tests are carried out with a drop-weight setup. The impactor with a specific weight will drop from identified height to strike the test specimen surface which is perpendicular to the falling path. The impact energy can be determined by converting gravitational potential energy into kinetic energy [22]. Thus, the higher impact energy will imply greater penetration of the test specimen while harder material will cause less penetration. The determination of impact energy can be achieved by changing the initial height of the impactor without changing the mass. The impact energy, E i in Joule is calculated as in Eq. (1).

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E i = Mi g Hi =

1 Mi Vi2 2

(1)

where M i is the mass of the impactor (kg), g is the acceleration due to gravity (m/s1 ), H i is the initial height of the impactor (m), and V i is an impact velocity (m/s). Thus, if the mass of the impactor, M i is 2 kg and the initial height of the impactor, H i is 1.0 m, the impact energy, E i can be valued as 19.62 J and V i is 4.43 m/s. The LVI test was carried out based on [23] in order to establish the experimental work. LVI tests were conducted using a drop weight machine model Instron 9250HV as shown in Fig. 1. The machine allows change of drop weight, height (up to 2 m), and impact velocity (up to 20 m/s). The test specimen was clamped to the impact rig drop tower according to [23]. The hemispherical impactor tip dropped is dropped to the test specimens at a specific height. The mass of the impactor used in this study is 2.0 kg and the impactor tip diameter is 16 mm. Fig. 1 Experimental setup of IID test

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2.2 Signal Acquisition of Impact-Induced Delamination in FGLC Material The scanning inspection of various of the IID in FGLC plates after low-velocity impact has been discussed. The UT A-scan signal from the identified impact area in FGLC plates using ISI i-InspeX TWO. In this study, a total of sixty specimens have been employed for scanning inspection, in which each type of the IID contained ten specimens. Based on the scanning inspection for various test specimens, the highest extensive area is 70 mm in length. Thus, the scanning envelope in this study has been fixed to be 80 mm in length by 80 mm in width for each sample from the impact point as illustrated in Fig. 2. The scanning resolution is set to be 1 mm for each scanning point within the scanning envelope, which is resulted in 6400 signals for each sample. Delamination can be detected from ultrasonic A-scan signal as the DWE peak signal exceed the gate setup (threshold limit), which is above 20% of full-screen-height (FSH). The location of delamination from the top surface of the specimen can be identified based on the distance between FWE to DWE. Then, all these signals either delamination or non-delamination have been re-plotted before the IID can be visualized as illustrated in Fig. 3. Although the location of delamination from the top surface of the specimen can be determined, there is no significant difference has been recorded because the thickness of the specimen used in this study is just 3 mm only. The location analysis of delamination in composite could be beneficial if involved with a thicker sample that is more than 5 mm thick [24].

Fig. 2 Scanning envelope of FGLC plate inspection

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Fig. 3 Ultrasonic A-scan signal in scanning envelope area

2.3 Signal Segmentation The signal segmentation of the obtained ultrasonic A-scan signal of various IID in FGLC plates has been discussed. The determination of the region of interest (ROI) for all signals is an essential signal pre-processing step before the unwanted signal can be eliminated. In this study, the data located in the initial pulse region and after the BWE region are considered irrelevant as the data gives no unique patterns against a different type of damage. This is because the most important region that needs to be focused on is within FWE to BWE region only. After several repeating signal segmentation processes, it was found that the best coverage signal which is from FWE to BWE is within 500 data. Thus, the length of ROI for all signals in this process has been proposed at 500 data. Besides, based on this process, an automated signal segmentation has been developed. The system will automatically determine the peak signal of FWE using the ‘find peak’ algorithm, and then start the ROI at 50 data before the peak signal of FWE until exceeding the BWE region, which is 500 data lengths. As a result, this proposed system is applicable to the inconsistent distance between the transducer to the test specimen surface.

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2.4 Feature Extraction The features of the re-plotted ultrasonic A-scan signal for various type of the IID has been extracted into several useful scalar features (one-dimensional form) such as mean, standard deviation, and percentage area of delamination over total scanning envelope size, and maximum delamination diameter in the horizontal and vertical direction. An ultrasonic A-scan signal has been obtained at a specific impact area in the scanning envelop region. The scanning resolution has been set to within 1 mm × 1 mm. Thus, the total signal acquired for each specimen is 6400 signals, whereas the scanning envelope size is 80 × 80 signals. 60 specimens have been employed in this stage whereas all these signals are then re-plotted into the visual-based mapping of delamination. There are six features to be extracted from each re-plotted ultrasonic A-scan signal for each type of delamination including mean, variance, standard deviation, the percentage area of delamination, and the maximum delamination diameter in the horizontal and vertical directions.

2.5 Signal Classification Using the ANN Approach The classification structure contained 6 types of delamination including no-damage (labeled as C1) as a reference purpose. The type of delamination is basically based on impact energy, where the impactor was initially dropped from different heights starting from 0.5 m for the C2 specimen, 1.0 m for C3, 1.5 m for C4, 2.0 m for C5, and 2.5 m for C6 specimen. Thus, the type of delamination is labeled as C1, C2, C3, C4, C5, and C6. The feed-forward back propagation neural network (BPN) architecture has been selected to classify different types of IID. The BPN architecture consists of multiple layers of nodes linked to each other. Each node acts as a neuron with a nonlinear activation function in the hidden layer of BPN. There are three layers of BPN called input, hidden layer, and output as shown in Fig. 4. Meanwhile, the input layer used six nodes represented as selected features. The number of neurons is determined by the model tested based on the measured configuration from the total number of cases. The best configuration throughout accuracy value is selected before the result is obtained at the output layer.

3 Results and Discussion 3.1 LVI Test Result of FGLC Plates Figure 5 shows a series of impact damage images of FGLC plates after conducting an LVI test for each impact test class. Six classes of impact tests are labelled as C1–C6.

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Fig. 4 Network architecture of the proposed classification system

The images of impact damage in Fig. 5 represent all the classes of impact damage including no damage. Figure 5a represents the test specimen without any damage. This specimen is labelled as C1 and used as a reference. The diameter of impact damage of the C2 specimen as in Fig. 5b is 15 mm in both horizontal and vertical directions. The impact energy and impact velocity applied to the C2 specimen are 9.81 J and 3.13 m/s respectively. The impact damage diameter is increased to 22 mm for the C3 specimen as in Fig. 5c after experiencing 19.62 J of impact energy and 4.43 m/s of impact velocity. Again, the impact damage diameter of the C4 specimen as in Fig. 5d is increased to 32 mm when the impact energy and velocity increase to 29.43 J and 5.42 m/s respectively. The impact damage diameter of the C5 specimen as in Fig. 5e is 40 mm while the C6 specimen as in Fig. 5f is 48 mm. Detailed results of impact damage diameter against impact energy of each test specimen can be found in Appendix F. Based on the study, it was found that the increase of impact damage size is proportional to the increase of the impact energy experienced to the FGLC plates, where the addition of 9.81 J of impact energy will increase the impact damage diameter in the range of 7–10 mm in length. This is because, fiberglass-based material is brittle, which is allow very little energy absorption when experiencing an impact [25]. Besides, there are no significant differences in impact damage diameter between the horizontal and vertical directions. Based on this observation, it can be concluded that the damage which is caused by an impact on FGLC plates is extensive in all directions. In fact, the impact of damaged propagation depends on the characteristic and structural integration of anisotropic material, which is influenced by the process design of the material such as the determination of plies angle, lay-up, and curing process [26]. The correlation between the impact energy and the diameter of impact damage in FGLC plates has been presented in Fig. 6. The range of impact damage size in terms of diameter of class 2 (C2) test specimen is between 15 and 21 mm while the C3 specimen is between 22 and 30 mm. The range of impact damage diameter keeps increasing up to 38 mm for the C4 specimen and up to 46 mm for the C5 specimen as the impact energy increased. The C6 specimen is between 48 and 56.50 mm. Based on this graph, it can be concluded that the size of impact damage in FGLC plates is proportional to the impact energy specific for low-velocity impact cases. Besides the diameter of impact damage, another data that require to obtain during the investigation of the behaviour of impact damage with the changes of impact

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Fig. 5 IID image of FGLC plates for each LVI test class. a Sample C1, b sample C2, c sample C3, d sample C4, e sample C5 and f sample C6

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Fig. 6 Influence of the impact energy to the diameter of impact damage

energy in FGLC plates is the area of impact damage. In this study, the area of impact damage is obtained by using an image processing software namely imageJ as illustrated in Fig. 7. Prior to the area can be obtained; the specimen image is processed in order to discriminate between the damaged area and the no-damage area by using an image threshold setup in binary format. Then, the damaged region which is represented by a white in colour has been selected. The calculation is made based on the total number of the selected pixel over the calibrated scale. The impact energy to the area of impact damage in FGLC plates has been presented in Fig. 8. As a result, the range of impact damage area of class 2 (C2) test specimen is between 365.03 and 515.15 mm2 while the C3 specimen is between 505.89 and 719.25 mm2 . The range of impact damage areas for C4 and C5 is 779.95–903.31 mm2 and 962.74–1150.54 mm2 . The C6 specimen is between 1220.14 and 1420.74 mm2 . Thus, the impact damage area of 3 mm thick FGLC plates after experiencing LVI up to 7 m/s to the changes of impact energy.

3.2 Detection of the IID Using Ultrasonic Immersion Testing Method The signal acquisition of the A-scan signal is divided into two types of patterns; damage and no-damage as illustrated in Fig. 9. The damage locations that can be obtained from the distance of FWE and DWE in A-scan signal are neglected because

Damage Detection of Impact-Induced Fiber Glass Laminated … Fig. 7 FGLC impacts damaged area

Fig. 8 Correlation between the impact energy to the impact damage area

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Fig. 9 UT A-scan signal a no-damage b damage

the specimen used in this study is thin, whereas there are no significant differences in damage location for each scanned point. Moreover, the focus of the study is to identify the delamination behaviour (after LVI test) against the changing of impact energy. The difference between damage and no damage of signal pattern can be determined based on the magnitude of the DWE peak signal. Thus, the signal pattern that represents ‘no-defect’ and ‘defect’ can be achieved in Fig. 9a and b respectively.

3.3 Signal De-noising Result Several wavelet families have been applied during de-noising the ultrasonic A-scan signal in order to identify and propose the best wavelet families that produce the highest pattern of similarity against the raw signal. The result of the de-noised signal using several types of wavelet families in the fourth level of decomposition is presented in Fig. 10. Figure 10a indicates the raw signal of delamination in the FGLC plate while Fig. 10b–g indicated the de-noised signal using Haar wavelet, Daubechies 2, Coiflets 2, Symlets 2, Biorthogonal 2.2, and Biorthogonal 4.4 respectively. A specific technique which is cross-correlation is used to distinguish the different patterns produced by the wavelet families. The highest cross-correlation value indicates a degree of similarity between the de-noised signals and the raw signal. Based on the cross-correlation result, Wavelet Biorthogonal 4.4 gives the highest cross-correlation value which is 797995.2 followed by the Biorthogonal 2.2 and Coiflets 2 which are 788,231.4 and 777,211.6 respectively. Symlets 2 and Daubechies 2 show the same results which are 761,313.7 because both of them have the same coefficient of reconstruction of a low pass filter.

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Fig. 10 Filtered signal from different type of wavelet families a raw signal, b Haar, c Daubechies 2 and d Coiflets 2, e Symlets 2, f Biorthogonal 2.2, and g Biorthogonal 4.4

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3.4 Delamination Image Based on Re-plotted UT A-Scan Signals Once the signal denoising process has been completed, the de-noised signals which are either indicate damage or no damage are re-plotted back based on the grid map in a scanning envelop area to visualize the delamination as illustrated in Fig. 11. The damage or no-damage signal can be determined according to the appearance of DWE in A-scan signal. Figure 12 presents the delamination images based on a different type of impact energy from ultrasonic A-scan signal. Figure 12a to represents the no-damage specimen which is labelled as C1 while Fig. 12(b–f) represent class 2 (C2) specimen which is has been impacted with 9.81 J of impact energy, C3 specimen (19.62 J), C4 specimen (29.43 J), C5 specimen (39.24 J) and C6 specimen (49.05 J) respectively. In general, it was found that the delamination size increase when the impact energy increase. In addition, the delamination image that has been presented from an ultrasonic A-scan signal is in a circle shape pattern. Thus, it is indicated that the delamination growth induced by the impact is consistently extended to all directions of the specimen. On top of that, based on the comparative analysis between the

Fig. 11 Visualize image of IID in FGLC plates

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Fig. 12 Visual image of UT A-scan signal in different impact energy

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Table 1 Percentage difference between the size of impact damage and delamination area Specimen class

Impact damage area (mm2 )

Delamination area from A-scan signal (mm2 )

Percentage of different (%)

C1

0

0

0

C2

365.03

488.05

33.70

C3

505.89

687.05

35.90

C4

779.95

1031.87

32.30

C5

962.74

1278.52

32.80

C6

1220.14

1645.97

34.90

delamination image from the ultrasonic A-scan signal and the impact image obtained of the first batch of each specimen as tabulated in Table 1, the delamination area has been extended more than thirty percent wider than the size if impact damage, which has been measured from the top surface of the test specimen. The detailed size of the delamination for each specimen is tabulated in Appendix G.

3.5 Delamination Measurement Result The results of comparative analysis between two types of measurements are taken from ultrasonic testing (categorized as NDT-based method) and visual inspection of the cross-section along with the delamination in FGLC plates (categorized as DTbased method). Figure 4.14 show the cross-section image of delamination in C2.1 FGLC. Figure 13a shows the overall image of the C2.1 test specimen after cross-sectional cut while Fig. 13b and c are the close-up image of damage and no damage respectively. Based on the cross-section image as in Fig. 13d, it can be found that the length of the delamination is 26 mm. Furthermore, the three different elements of damage that are induced by an impact have been presented in Fig. 13b where the perforation, delamination, and fiber breakage existed. Besides, the separation layer between each fiber has been spotted in several location points in the same image. Since one of the objectives in this study is to verify the measurement result from the ultrasonic testing method based on the DT-based method, this verification analysis has not been applied to all the test specimens. In addition, this method requires a lot of time and also is exposed to the uncertain result which is the damage might become even worst after the cross-section cutting process. Based on the three specimens (C2.1, C2.2, and C2.3) which are applied in this DT-based verification analysis, the damage length is between 27 and 29 mm as in Table 2. The average percentage of the difference between NDT-based and DT-based diameter measurement results is 4.72%.

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Fig. 13 Cross-section image of delamination in FGLC material

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Table 2 Percentage of difference between NDT and DT measurements Specimen class

Horizontal delamination diameter from NDT measurement, Ddx (mm)

Horizontal delamination diameter from DT measurement, DT_Ddx (mm)

Percentage of different (%)

C2.1

27.00

26.00

3.70

C2.2

29.00

27.00

6.90

C2.3

28.00

27.00

3.57

AVERAGE

28.00

26.67

4.72

3.6 Classification Result of the Impact-Induced Delamination in FGLC The classification accuracy result is based on a fivefold cross-validation test to classify six types of delamination denoted as C1, C2, C3, C4, C5, and C6. Based on the classification result, it was found that the classification accuracy of the proposed system is nearly 100%. In specific, the classification accuracy is in the range from 99.29% at Fold-5 to 99.80% at Fold-1 and Fold-3. Overall, the average classification accuracy is 99.54%. Thus, it can be concluded that the proposed network is successful to classify the different types of damage. In addition, it also indicated that the selected features for the classification input are useful and accurate. Besides classification accuracy, the number of neurons gives a significant contribution in order to obtaining good classification results. To determine the appropriate number of neurons, all the classification inputs have been tested using the same classification parameter. As a result, the relationship between classification accuracy and the number of neurons is plotted in Fig. 14. Thus, a network with 12 neurons resulted in the highest classification performance which is 99.80% before it decreases to 87.32% when the number of neurons increases to 13 neurons. Therefore, 12 neurons have been chosen in this study because it gives the highest classification accuracy score as compared the to others number of neurons as illustrated in Fig. 14. In this study, the validation of the network’s classification accuracy is based on the mean square errors (MSE) against the number of epochs during training, validating, and testing the network. MSE is used to measure the network’s performance throughout the mean of squared errors while the epoch is an iteration during the training of the vector that is used to update the weight. Thus, to obtain the highest classification accuracy, the training networks are focused to achieve the lowest number of MSE. To analyze the performance of the proposed network, each fold is validated using MSE versus the epoch graph plotting as illustrated in Fig. 15.

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Fig. 14 Classification performance of difference no of neurons

Fig. 15 MSE of network fold-3 (99.37%)

4 Conclusion An investigation of the onset of the delamination in FGLC plates in this study has identified that the delamination area is extended internally up to 35.90% over the impact damage area which is obtained from the specimen surface and the damage propagation occurs in all directions. Furthermore, the rate of delamination area with the changes of the impact energy is between 23 and 45%. Thus, the detection of impact damage delamination using ultrasonic has shown to be an effective method

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for detecting the impact-induced delamination (IID) in FGLC plates. The developed algorithm of dynamic segmentation has found able to segment the A-scan signal automatically according to the specific length distance, regardless of the variation in gap distance between transducer and specimen surface which is up to 13 mm. In the following process, it was found that the mother wavelet namely Biorthogonal 4.4 gives the highest maximum cross-correlation value as compared with the other type of mother wavelets. The selection of signal features, however, is based on the delamination image which it has been visualized from the ultrasonic A-scan signal whereas six features have been chosen which is based on delamination size such as delamination area and diameter in horizontal and vertical direction, mean of damage point, variance and standard deviation as well. The classification accuracy of the IID in FGLC plates is exceeded 99.29%. Based on this result, it is indicated that the selected features for the classification input is accurate and the use of an artificial neural network from an ultrasonic A-scan signal has shown it applicability to classify the different type of the IID in FGLC plates.

5 Recommendation The biggest difficulty in detecting the IID using ultrasonic immersion testing is to determine the origin point of scanning envelop area as it is important for damage mapping and also necessary during visualizing the delamination. Thus, more research work is needed in the future in order to overcome these issues. The use of unsupervised or self-organized learning classification to classify different types of delamination has not yet been explored in IID especially in FGLC material as it requires extensive analysis to develop an algorithm that is able to learn rapidly for the advanced application. Acknowledgements The authors would like to thank Universiti Tun Hussein Onn Malaysia (UTHM) for its financial support through the Tier 1 Grant No H925

References 1. Hubert P, Centea T, Grunefelder L, Nutt S, Kratz J, Levy A (2017) Out-of- Autoclave Prepreg Processing. Comprehensive Composite Materials II. Amsterdam UK, Elsevier 2. Perez M, Gil L, Oller S (2014) Impact damage identification in composite laminates using vibration testing. Compos Struct 108:267–276 3. Nikfar B, Njuguna J (2014) Compression-after-impact (CAI) performance of epoxy-carbon fibre-reinforced nanocomposites using nano silica and rubber particle enhancement. IOP Conf Series: Mater Sci Eng 64:1–6 4. Lin M, Chang F (2002) The manufacture of composite structures with a built-in network of piezoceramics. Compos Sci Technol 62:919–939 5. Sayer M, Bektas MB, Demir E, s& Calliog‘lu F. (2012) The effect of temperatures on hybrid composite laminates under impact loading. Compos B Eng 43:2152–2160

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6. Liu J, Zhu X, Li T, Zhou Z, Wu L, Ma L (2014) Experimental study on the low velocity impact responses of all-composite pyramidal truss core sandwich panel after high temperature exposure. Compos Struct 116:670–681 7. Jang BW, Kim CG (2017) Real-time detection of low-velocity impact-induced delamination onset in composite laminates for efficient management of structural health. Compos B 123:124– 135 8. Chandarana N, Sanchez DM, Soutis & C., Gresil M. (2017) Early damage detection in composites during fabrication and mechanical testing. Material 685:1–16 9. Yu F, Wu Q, Okabe Y, Kobayashi S, Saito K (2016) The identification of damage types in carbon fiber-reinforced plastic cross-ply laminates using a novel fiber—optic acoustic emission sensor. Struct Health Monit 15:93–103 10. Kudelaa P, Wandowskia T, Malinowskia P, Ostachowicza W (2017) Application of scanning laser Doppler vibrometry for delamination detection in composite structures. Opt Lasers Eng 99:46–57 11. An YK (2016) Impact-induced delamination detection of composites based on laser ultrasonic zero-lag cross-correlation imaging. Adv Mater Sci Eng 2016:1–8 12. Mitrevski T, Marshalla H, Thomson R (2006) The influence of impactor shape on the damage to composite laminates. Compos Struct 76:116–122 13. Tian Z, Yu L, Leckey C, Seebo J (2015) Guided wave imaging for detection and evaluation of impact-induced delamination in composites. Smart Mater Struct 24:1–13 14. Caprino G, Spataro G, Luongo SD (2004) Low-velocity impact behaviour of fiberglass– aluminium laminates. Compos A Appl Sci Manuf 35:605–616 15. Harizi W, Chaki S, Bourse G, Ourak M (2015) Mechanical damage characterization of glass fiber-reinforced polymer laminates by ultrasonic maps. Compos B 70:131–137 16. Dua R, Watkins SE, Wunsch DC, Chandrashekhara K, Akhavan F (2001) Detection and classification of impact-induced damage in composite plates using neural networks. In: Paper presented at IJCNN 2001: IEEE international joint conference on neural networks. Washington, USA 17. Watkins SE, Akhavan F, Dua R, Chandrashekhara K, Wunsch DC (2007) Impact-induced damage characterization of composite plates using neural networks. Smart Mater Struct 16:515–524 18. Gaudenzi P, Nardi D, Chiappetta I, Atek S, Lampani L, Pasquali M, Sarasini F, Tirilló J, Valente T (2017) Sparse sensing detection of impact-induced delamination in composite laminates. Compos Struct 133:1209–1219 19. Meola C, Boccardi S, Carlomagno GM, Boffa ND, Monaco E, Ricci F (2015) Nondestructive evaluation of carbon fibre reinforced composites with infrared thermography and ultrasonics. Compos Struct 134:845–853 20. Qihui C, Ting L, Yingju G, Zhi W, Yaqing L, Ruikui D, Guizhe Z (2017) Mechanical properties in glass fiber PVC-foam sandwich structures from different chopped fiber interfacial reinforcement through vacuum-assisted resin transfer molding (VARTM) processing. Compos Sci Technol 144:202–207 21. Junliang D, Byungchil K, Alexandre L, Peter M, Nico D, Citrin DS (2015) Nondestructive evaluation of forced delamination in glass fiber-reinforced composites by terahertz and ultrasonic waves. Compos B 79:667–675 22. Zhang D, Fei Q, Zhang P (2017) Drop-weight impact behaviour of honeycomb sandwich panels under a spherical impactor. Compos Struct 168:633–645 23. ASTM D7136 (2012) Standard test method for measuring the damage resistance of a fiberreinforced polymer matrix composite to a drop-weight impact event. In: ASTM International: West Conshohocken, Pennsylvania 24. Gan KW, Allegri G, Hallett SR (2016) A simplified layered beam approach for predicting ply drop delamination in thick composite laminates. Mater Des 108:570–580 25. George CJ, John FF, Srdan S, Starbuck JM (2002) Energy absorption in polymer composites for automotive crashworthiness. J Compos Mater 36:813–850 26. Malhotra A, Guild FJ (2014) Impact damage to composite laminates: effect of impact location. Springer, New York

Microperforated Panel Made by Biodegradable Natural Fiber Composite for Acoustic Application Desmond Daniel Vui Sheng Chin, Musli Nizam bin Yahya, and Nazli bin Che Din

1 Introduction There is no doubt that synthetic fibre is still one of the best sound absorber available [1]. It remains as the most popular selection among acousticians due to its excellent sound absorption capabilities. The existence of huge amount of cavity network within the porous structure of synthetic fibre contributes to its high permeability level [2]. When a sound wave strikes the synthetic fibre, the porous structure of synthetic fibre forces sound wave to reflect randomly within the cavity network. The sound energy is deteriorated due to the reflection of sound wave and therefore, the sound energy will be absorbed. [3, 4]. Concern arises as a great deal of studies clarified that synthetic fibre such as fibreglass and rockwool could be fatally impair on our health condition after long exposure [5]. The detrimental effect of synthetic fibre prompts the urge of finding a better alternative to replace synthetic fibre for absorbing sound energy application. Natural fibre is an potential material in order to replace the synthetic fibre for sound absorption application. It have been proven by many studies investigating the potentiality of natural fibre as a sound absorption material. However, there are new method can use for sound absorption which is micro-perforated panel or called MPP. It was proposed by Maa [6–9] for replacing the fibre for sound absorber application. MPP is largely made from thin metallic plate such as steel and aluminium with a numbers of perforated holes that usually occupies not more than 2% of the surface area on the panel [10, 11]. Basically, the MPP’s thickness is usually equals to 1 mm D. D. V. S. Chin · M. N. bin Yahya (B) Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, Batu Pahat, Johor Darul Takzim, Malaysia e-mail: [email protected] N. bin Che Din Faculty of Built Environment, University of Malaya (UM), 50603 Kuala Lumpur, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_4

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Fig. 1 Schematic drawing of MPP with air space between rigid wall

or much lesser and same goes to the perforated holes of MPP where the diameter of the perforated holes are usually could be equal to 1 mm or much lesser as well [12]. MPP must be solid and rigid in order to prevent any additional vibration or noise to occur [13]. It also must be installed with air space between wall as shown in Fig. 1 [14]. To predicting the sound absorption of MPP, Maa continued Rayleigh’s and Crandall’s work on the acoustic impedance and successfully derived an approximate model of MPP by making an assumption that each perforated hole on the surface of MPP can be taken as a small cylindrical tube [15–18]. Combining all of the perforated holes of MPP based on the perforation ratio of a MPP (usually between 1 and 2%), all of the perforated holes could be treated as a network of small tubes. If the length of an incident sound wave is greater in comparison to the diameter of the perforated hole, the perforated hole can be well expressed by the following equation where Maa treated the perforated hole as a mere thin cylindrical tube [18]: [ Z = 1−

(

( √ ) )( )]−1 J1 ξ − j 2 ( √ ) × ωρt j √ ξ −j J0 ξ − j √ ξ = ro ωρ/η j=

√

−1

(1) (2) (3)

In this expression, the incident of sound wave at the angular frequency is denoted by ω, the density of the surrounding air is denoted by ρ, the thickness of the MPP is denoted by t, the radius of the perforated hole on the MPP surface is denoted by

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r o , the dynamic viscosity of air is denoted by η, and the zeroth and first order for Bessel functions of the first kind are denoted by J 0 and J 1 respectively. By dividing Eq. (1) with the perforation ratio of the MPP, the approximate acoustic impedance of MPP could be attained. But, on Eq. (1) derived by Maa was inconvenient and lack of practicability due to the existence of convoluted mathematical functions and hence, Maa introduced a better approximate model which is simpler, straightforward, and more practical with a comparative error of less than 5% [16]. After simplification, the acoustic impedance was stated as [16, 19]: Z = RM P P + j X M P P , Z0 (√ √ ) dχ 2 C1 t χ2 + RM P P = 2 1+ × 10−5 , d p 32 8t ⎞ ⎛ 1 0.0185t f ⎝ 0.85d ⎠, + √ XMPP = 1+ p t χ2 9+ 2 ZMPP =

χ = C2 d

√

f × 10−3

(4)

(5)

(6)

(7)

The acoustic impedance of air is denoted by Z o , the resistance and reactance of MPP are denoted by RMPP and X MPP respectively, constant value C 1 and C 2 are 0.147 and 0.316 for MPP made of non-metallic material and 0.335 and 0.21 for MPP made of metallic material, the frequency of incident sound wave is denoted by f , and the diameter of the perforated hole is denoted by d. Finally, the normal incident condition MPP’s sound absorption is stated as [20–22]: α=

4R M P P (1 + R M P P ) + [ω × X M P P − cot(ω D/C0 )] 2

(8)

where the speed of the incident wave or sound is denoted by C o . As mentioned previously, Mostly, the MPP are made from metal, steel and aluminium. Yet, the major production of steel and aluminium dissipates an enormous amount of carbon and heat to our atmosphere, therefore, it increase the global temperature in a very alarming rate, perniciously harming our dear environment [23, 24]. Natural fibre has been proposed as one of the alternative that could be utilize to replace synthetic fibre for sound absorption application. Due to natural fibre biodegradable properties, it has been acknowledged as a green material for quite some time. [25–27]. Natural fibre also has been considered as a renewable source as an ample supply of natural fibre could be found all across Asian countries [28–33]. Plenty of studies proved that natural fibre such as kenaf fibre, coconut fibre, and bamboo fibre have excellent sound absorption abilities [25] However, natural fibre alone is weaker in comparison to synthetic fibre and will not be able to go through any kind of mechanical processing, triggers the intention among researchers

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to explore the natural fibre composite on the acoustic properties. E. Jayamani and S. Hamdan explored the performance of sound absorption of natural fibre composite (kenaf + polypropylene) and results showed that the composite has much lower sound absorption compared to pure natural fibre content [34]. Therefore, in this paper, an idea of incorporating both idea to eliminate the downside of each cases, biodegradable natural fibre composite form in micro-perforated panel (BNFC-MPP) was proposed. In this study, kenaf fibre mixes with polylactic acid (PLA) to generate biodegradable polymer which uses to produce BNFC-MPP. The sound absorption of BNFC-MPP will be explored in this paper. Moreover, the air gap effects between BNFC-MPP and tradional MPP also will be presented.

2 Material and Experiment Kenaf fibre (powder form) and polylactic acid were obtained in Malaysia sources. The density of kenaf fibre and polylactic acid are 1.4 g/cm3 and 1.24 g/cm3 respectively. The tensile strength of kenaf fibre and polylactic acid are 930 MPa and 50 MPa respectively. Meanwhile, the tensile modulus of kenaf fibre and polylactic acid are 53 MPa and 3500 MPa respectively. Figure 2 shows the design of BNFC-MPP sample along with a copy of sample prepared. Mixing machine (Brabender Mixer – Plastograph EC) was applied to mix both kenaf fibre and PLA resin to procure a composite. In this study, portion of 30% and 70% for kenaf fibre and PLA resin, respectively were mixed for the fabrication of BNFC-MPP sample. The materials were allowed to mix for about 10–15 min so that both materials could be mixed thoroughly. Figure 3 shows the mixing machine applied to mix both kenaf fibre and PLA resin.

(a)

(b)

Fig. 2 a Schematic diagram of BNFC-MPP, b actual sample of BNFC-MPP

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Fig. 3 Mixing machine used in this study

The composite obtained from the mixing machine then undergo pelletization process to procure composite in pellet form through the usage of a granulator. Figure 4 shows the granulator used to pelletizes the composite obtained from mixing machine. Then, the pellets were uniformly distributed across a 1 mm thick mold and underwent hot compression process by using a hot compression machine (WABASH 30 Ton Genesis Steam Heated Platen Press Model G302 – CX). Figure 5 shows the hot compression machine used in this study. Before the hot compression process, it is very important that the pellets should be allowed to undergo 15 min of pre-heating process to ensure that the pellets could be melt and uniformly distributed on the surface of the mold. The pellets were compressed with ten tonnes of pressure within 10 min on hot compression machine with the temperature 175 °C in accordance with the melting standard of temperature of PLA resins. Then, the hot compression machine will cooldown until it reaches temperature 30 °C. A 1 mm thin natural fibre composite panel was produced from the previous hot compression process. The thin panel then underwent perforation process by using a mini electric hand drill as shown in Fig. 6. The diameter of the perforated holes were 1 mm and the perforation ratios were 1% of the surface area. The perforation process was the final procedure for the completion BNFC-MPP sample fabrication operation. The BNFC-MPP sample was then inserted into Brüel & Kjær (B&K) Impedance Measurement Tube Type 4206 (Software AFD 1001), The sound absorption measurement of BNFC-MPP sample follows the guideline stated and provided in

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Fig. 4 Granulator used in this study

ASTM E1050-2 (ISO 10534-2) standard [35]. Figure 7 shows the experimental setup of the impedance tube along with the BNFC-MPP sample for measurement purposes. The BNFC-MPP sample of sound absorption coefficient was determined within of 400–2000 Hz of frequencies. The characteristic of sound absorption coefficient of BNFC-MPP sample with a variation of air gap was measured.

3 Results and Discussion Figure 8 shows the BNFC-MPP’s sound absorption performance sample with the effect of different air gap (10, 20, and 30 mm). It is noticed that, the BNFC-MPP’s sound absorption coefficients sample in response with the effect of different air gap showed similar pattern where only one peak sound absorption coefficient has been recorded. When air particles near to the perforated hole vibrates, friction happens and causes the deterioration of acoustical energy and thus, absorbing sound. When the air particles vibrate more, the friction will be greater and thus, explaining the phenomenon of the increment of sound absorption coefficient value recorded. The upsurges of the thickness of air gap behind the BC-MPP sample causes the deviation

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Fig. 5 Hot compression machine

Fig. 6 Mini electric hand drill (Freebang – SKU370357)

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(a)

(b)

Fig. 7 a Impedance tube system, b sample setup in the impedance tube

on the absorption bandwidth of the panel. The increment of air gap also causes the peak absorption to shift closer towards lower frequency range. The BNFC-MPP sample with the air gap behind could be modelled as a simple mass and spring resonance relation where the perforated holes could be labelled as the acoustic mass and meanwhile the air within the air gap could be labelled as the acoustic spring [36, 37]. Once the thickness of the air gap increases, the stiffness of the acoustic spring gets weaker and hence, shifting phenomena was occurred on peak absorption nearer towards lower frequency range [36, 38, 39]. Figure 9 reveals the sound absorption performance for both BNFC-MPP and traditional MPP which is made of steel with 30 mm air gap [15]. Based on the graph obtained, BNFC-MPP possessed higher peak sound absorption coefficient in 1.0

Air gap 10mm Air gap 20mm Air gap 30mm

Sound Absorption Coefficient

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 400

600

800

1000

1200

1400

1600

1800

2000

Frequency (Hz)

Fig. 8 Sound absorption coefficient of BNFC-MPP samples with different air gap

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1.0 BC-MPP Conventional MPP

Sound Absorption Coefficient

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 400

600

800

1000

1200

1400

1600

1800

2000

Frequency (Hz)

Fig. 9 Sound absorption coefficient of BNFC-MPP compare with traditional MPP with air gap 30 mm

comparison to steel MPP, then, the peak sound absorption for BNFC-MPP noted 0.96 while the peak sound absorption for steel MPP indicates 0.83. The difference on the peak absorption between BNFC-MPP and steel MPP was evident as BNFC-MPP has 15.9% higher peak sound absorption coefficient compared to steel MPP. This is mainly due to the fact that the structure of BNFC-MPP consist of a large network of cavity and hence, contributing to the increment of porosity level of the panel [3]. As stated earlier, the advantage of porous media is that it could force the incoming sound wave that strikes the panel to enters and randomly reflect within the structure itself, causes the acoustical energy of the wave to degrade as the reflection happens and therefore, absorbing sound [4]. It can be noted that the bandwidth of absorption of BNFC-MPP was broader compared to steel MPP and hence, BNFCC-MPP could absorb sound at much wider frequency range compared to steel MPP.

4 Conclusion Overall, the study of the sound absorption performance of BNFC-MPP has been examined. Result shows that different air gap affect the sound absorption performance of BNFC-MPP by moving its peak absorption nearer to lower frequency range. Result also indicates that BNFC-MPP sample made out of natural fibre composite has higher sound absorption performance in comparison to steel MPP mainly due to the structural difference between BNFC-MPP and steel MPP. Overall, BNFC-MPP shows a really promising potential to be used as green sound absorber in near future

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as it is biodegradable, light weight, and environmentally more superior in comparison to synthetic fibre.

References 1. Wang C-N, Torng J-H (2001) Experimental study of the absorption characteristics of some porous fibrous materials. Appl Acoust 62(4):447–459 2. Jawaid M, Khalil HA (2011) Cellulosic/synthetic fibre reinforced polymer hybrid composites: a review. Carbohyd Polym 86(1):1–18 3. Ingard KU (1994) Notes on sound absorption technology (Book). Noise Control Foundation, Poughkeepsie 4. Lim Z, Putra A, Nor M, Yaakob M (2018) Sound absorption performance of natural kenaf fibres. Appl Acoust 130:107–114 5. Papadopoulos AM (2005) State of the art in thermal insulation materials and aims for future developments. Energy Build 37(1):77–86 6. Maa D-Y (1998) Potential of microperforated panel absorber. J Acoust Soc Am 104(5):2861– 2866 7. Falsafi I, Ohadi A (2017) Design guide of single layer micro perforated panel absorber with uniform air gap. Appl Acoust 126:48–57 8. Guo W, Min H (2015) A compound micro-perforated panel sound absorber with partitioned cavities of different depths. Energy Procedia 78:1617–1622 9. Qian Y, Zhang J, Sun N (2018) A strategy for extending the effective application of microperforated panel absorbers to high sound intensity. Appl Acoust 130:124–127 10. Fuchs HV, Zha X (2006) Micro-perforated structures as sound absorbers—a review and outlook. Acta Acust Acust 92(1):139–146 11. Bravo T, Maury C (2018) Sound attenuation and absorption by micro-perforated panels backed by anisotropic fibrous materials: theoretical and experimental study. J Sound Vib 425:189–207 12. Lee Y, Lee E, Ng C (2005) Sound absorption of a finite flexible micro-perforated panel backed by an air cavity. J Sound Vib 287(1):227–243 13. Wang C, Huang L (2011) On the acoustic properties of parallel arrangement of multiple microperforated panel absorbers with different cavity depths. J Acoust Soc Am 130(1):208–218 14. Qian Y, Zhang J (2018) Engineering-oriented design strategy to obtain linear micro-perforated panel absorbers at high sound pressure environment. Appl Acoust 137:40–44 15. Jung SS, Kim YT, Lee DH, Kim HC, Cho SI, Lee JK (2007) Sound absorption of microperforated panel. J Korean Phys Soc 50(4):1044 16. Dah-You M (1975) Theory and design of microperforated panel sound-absorbing constructions. Sci Sinica 18(1):55–71 17. Rayleigh JWSB (1896) The theory of sound. Macmillan 18. Crandall IB (1954) Theory of vibrating systems and sound. D. Van Nostrand Company 19. Maa D-Y (ed) (1983) Direct and accurate impedance measurement of microperforated panel. In: Inter-Noise and Noise-Con Congress and Conference Proceedings. Institute of Noise Control Engineering 20. Dah-You M (1997) General theory and design of microperforated-panel absorbers. Acta Acust 5 21. Dah-You M (2000) Theory of microslit absorbers. Acta Acust 6:000 22. Min S, Nagamura K, Nakagawa N, Okamura M (2013) Design of compact micro-perforated membrane absorbers for polycarbonate pane in automobile. Appl Acoust 74(4):622–627 23. Herrin D, Liu J, Seybert A (2011) Properties and applications of microperforated panels. Sound Vib 45(7):6 24. Wyckoff AW, Roop JM (1994) The embodiment of carbon in imports of manufactured products: implications for international agreements on greenhouse gas emissions. Energy Policy 22(3):187–194

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25. Yahya MN, Chin DD (2017) A review on the potential of natural fibre for sound absorption application. IOP Conf Ser: Mater Sci Eng 226(1):012014). IOP Publishing 26. Arenas JP, Crocker MJ (2010) Recent trends in porous sound-absorbing materials. Sound Vib 44(7):12–18 27. Faruk O, Bledzki AK, Fink H-P, Sain M (2012) Biocomposites reinforced with natural fibers: 2000–2010. Prog Polym Sci 37(11):1552–1596 28. Webber III CL, Bledsoe VK (2002) Kenaf yield components and plant composition. In: Trends in new crops and new uses, pp 348–57 29. Lau K-T, Hung P-Y, Zhu M-H, Hui D (2018) Properties of natural fibre composites for structural engineering applications. Compos Part B: Eng 136:222–33 30. Fan M (2017) Future scope and intelligence of natural fibre based construction composites. In: Advanced high strength natural fibre composites in construction, Elsevier, pp 545–56 31. Monteiro SN, Lopes FPD, Ferreira AS, Nascimento DCO (2009) Natural-fiber polymer-matrix composites: cheaper, tougher, and environmentally friendly. JOM 61(1):17–22 32. Fangueiro R, Rana S (2017) Advances in natural fibre composites: raw materials, processing and analysis. Springer 33. Mastura M, Sapuan S, Mansor M, Nuraini A (2017) Conceptual design of a natural fibrereinforced composite automotive anti-roll bar using a hybrid approach. Int J Adv Manuf Technol 91(5–8):2031–2048 34. Jayamani E, Hamdan S (2013) Sound absorption coefficients natural fibre reinforced composites. In: Advanced materials research, vol 701. Trans Tech Publications, pp 53–58 35. Standard A (1990) Standard test method for impedance and absorption of acoustical materials using a tube, two microphones and a digital frequency analysis system. In: ASTM Standard E, pp 1050–1098 36. Chin DDVS, Yahya MNB, Din NBC, Ong P (2018) Acoustic properties of biodegradable composite micro-perforated panel (BC-MPP) made from kenaf fibre and polylactic acid (PLA). Appl Acoust 138:179–187 37. Laly Z, Atalla N, Meslioui S-A (2018) Acoustical modeling of micro-perforated panel at high sound pressure levels using equivalent fluid approach. J Sound Vib 38. Liu Z, Zhan J, Fard M, Davy JL (2017) Acoustic properties of multilayer sound absorbers with a 3D printed micro-perforated panel. Appl Acoust 121:25–32 39. Liu Z, Zhan J, Fard M, Davy JL (2017) Acoustic measurement of a 3D printed micro-perforated panel combined with a porous material. Measurement 104:233–236

Fractographic Investigation and Mechanical Properties of Novel 7xxx Al-Alloy from Recycled Beverage Cans (RBCs) for Automotive Components Application A. Kazeem, H. N. Awwal, N. Z. Hassan, N. A. Badarulzaman, S. S. Jikan, and W. F. F. Wan Ali

1 Introduction Fractographic analysis of experimental alloys are beneficial to recommending aluminium alloys for engineering applications. When in application, say as in connecting rods or transmission components of engines, aluminium alloys may fail. It is therefore pertinent to relate the fracture characterization with the mechanical properties. This will support the choice of 7xxx alloys cast from recycled beverage cans (RBCs) for automobile applications as the volume of cast aluminium in the industry make up more than half of the aluminium used in cars [1]. Rana et al. [2] had predicted that the amount of aluminium in the automobile industry might increase to 180 kg. The United States of America (USA) sources over 95% of the aluminium A. Kazeem National Centre for Technology Management (NACETEM), Department of Science Policy and Innovation Studies, North Central Zonal Office, FCT-Abuja, Nigeria H. N. Awwal Department of Chemistry, Faculty of Science, Bauchi State Gadau, Gadau, Nigeria N. Z. Hassan · N. A. Badarulzaman (B) Nanostructure and Surface Modification Focus Group (NANOSURF), Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, Johor, Malaysia e-mail: [email protected] S. S. Jikan Faculty of Applied Sciences and Technology, Universiti Tun Hussein Onn Malaysia, Edu-Hub Pagoh, 84600 Pagoh, Johor, Malaysia W. F. F. W. Ali Faculty of Mechanical Engineering, Universiti Teknologi Malaysia (UTM), UTM-Skudai, 81310 Johor, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_5

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used in the automobile industry from secondary sources [3]. Electric vehicles (EVs) use about 50–200 kg aluminium alloys per car. For instance, the AUDI A2 and A8 EVs used about 300–550 kg of aluminium in fabricating components. Request for aluminium has consistently increased with about 4.5 kg per annum, suggesting that the future of aluminium alloys in the automobile industry is bright [4]. Earlier studies relating fracture surface investigation with mechanical properties were done using alloys fabricated using raw materials acquired from as-received. This chapter reports on Al–Zn–Mg–Cu alloy cast using 80% recycled materials, which offers a cheaper method of producing the 7xxx alloy for automotive application. The study by Ochoa et al. [5] analysed the effect of temperature and time on the variation of the concentration of Zn in Al–Zn–Mg alloy fabricated using recycled batteries. The study reported the possibility of preparing Al–Zn–Mg alloys containing up to 2.47 wt.% Zn. The relevance of the report by AlSaffar and Bdeir [6] was only on the economic relevance and chemical composition of RBCs. Juniarsih et al.’s [7] effort was relevant in reducing the composition of Mg in RBCs as 77.83% was reduced when holding time of 120 min was used during melting. The Al recovered reached 97.49% and suggest that RBCs are good sources of aluminium ingots. The aim of this report is to observe the differences in the fractographic texture of two categories of alloys and relate the fracture to the UTS and hardness of the alloys following ageing at 100 °C (Category A) and 120 °C (Category B).

2 Materials and Experiment 2.1 Materials Partly, the focus of this study was the conversion of recycled materials into new experimental 7xxx alloys. About 80% of the raw materials were soured from recycled sources. Basically, Al, Zn, Mg, Mn and Cu were the main constituents of this new Al–Zn alloy. Sourcing of the RBCs was done at recycling collection points in Batu Pahat, Malaysia. The beverage cans were cast into aluminium ingots using graphite crucible in a gas powered furnace. Zn and Mn were sourced from Hawk battery with GB/T 8897.2-2008 standard. The pieces of Zn were fabricated into ingots using JT0332 portable induction electric melting furnace. Cu sourced from windings of the coils of a table fan was cast into 70% Cu–30% Al to support the ease of melting Cu in the alloy.

2.2 Methodology Two categories of alloys tagged A and B with nine samples (A1–A9 and B1–B9) were cast with the intent of assessing the effect of ageing temperature on the alloys.

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Table 1 The variation in wt.% Zn, and artificial ageing parameters (a) 100 °C artificial ageing temperature

(b) 120 °C artificial ageing temperature

Sample

Sample

Zn (wt.%)

Artificial ageing time (hours)

Zn (wt.%)

Artificial ageing time (hours)

A1

4

6

B1

4.5

6

A2

5

15

B2

4

6

A3

5

15

B3

4.5

10.5

A4

4.5

10.5

B4

4.5

15

A5

5

6

B5

5

10.5

A6

4

6

B6

5

15

A7

4.5

10.5

B7

5

10.5

A8

5

6

B8

4

10.5

A9

4

15

B9

4.5

15

The wt.% Zn was varied from 4.00 to 5.00 wt.%. Other constituents like Mg, Mn and Cu were held at 1.5 wt.%, 1 wt.% and 0.35 wt.% respectively. Casting commenced by preheating the crucible as Al, Zn, 70% Cu–30% Al, Mn and Mg were introduced afterwards. Consistent stirring of the alloy was achieved by setting a TAC 1803-Pentec portable mechanical mixer at 7th speed of ± 550 RPM. Molten alloys were poured into steel pipes serving as the mould as the temperature was observed to be about 670 ± 10 °C with the aid of a Series 472 digital thermocouple thermometer. Tensile test samples were machined in accordance with the ASTM E8/E8M-11 specifications using Mazak Nexus 100-II universal CNC Lathe machine. Heat treatment was achieved using the Nabertherm B180 MB2 furnace. All samples were solution treated at 450 °C using clean water at room temperature as the cooling medium. The ASTM designated as B 557 M-02a was used in performing the tension test on Gotech AI-7000 LA5 Servo controlled Universal Tensile test machine. Fractographic and microstructure samples were sectioned out from each sample following the heat treatment specifications outlined in Table 1. Vickers microhardness was conducted using ASTM E92-17 specification on Shimadzu HMV-2, C227-E013 machine. Load, duration for test and times of test were set at 490.3 mN (0.05 HV), 10 s and 9 respectively. Preparation of sample surface was done with the aid of silicon carbide grit paper of 240. 320, 400, 600 grades on a Buehler manual grinding machine while maintaining consistent flow of water.

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3 Results and Discussion The resultant effect of the surface and internal integrity of the material was a reflection of the mechanical properties. The failure mechanism is herein presented and juxtaposed with the microstructure and the mechanical properties of the experimental alloy.

3.1 Fractographic Morphology Analysis The postmortem analysis of the morphology of samples were conducted to link the characterization with the failure mechanism and the obtained mechanical properties of the fabricated alloys. When the fractured surface was carefully observed, relevant information on the specific roles of heat treatment, intrinsic microstructural effects on UTS and ductility properties of the aluminum alloy fabricated from RBCs. A macroscopic assessment of the fracture surfaces revealed little differences in overall fracture morphology as for the intrinsic pattern of the failure mode. The surfaces were bumpy and basically normal to the stress axis. When subjected to microscopic analyses, observable cracks and recrystallized grain structures were observed with failure lines due to multiple cracks generated from primary points. The formation of second phase particles aided the transgranular fracture. Though the formation of precipitates is beneficial to mechanical properties, they may equally serve as formation of pockets of shallow dimples and microscopic voids of varying size. The analysis revealed that fracture behavior is related with the heat treatment and elemental content for the samples. Figure 1a depict the cup and cone fracture observed in sample with 5 wt.% Zn following artificial aging at 100 °C for 15 h. The ductility of the alloy was demonstrated in the tear ridges shown in Fig. 3a. Dimples and quasi-cleavage were evidences of the load required in testing the alloy to failure under tension. The macro investigation of the fracture surface in combination with Fig. 1d suggest that the failure commenced on a plane that was about 45° to the tensile axis. The fracture surface in Fig. 1b was characterized by tear ridges demonstrating the effect of the load leading to the fracture. The elemental analysis revealed the presence of 6.66 wt.% Mg and 2.97 wt.% Zn as a demonstration of the possible formation of the hardening precipitates of MgZn2 . The study conducted by Dai et al. [8] was concurrent with the investigation herein presented wherein disc-like precipitates distributing along grain boundaries were demonstrated to be equilibrium η (MgZn2 ) precipitates responsible for change in mechanical properties. It should be noted that the 119.28 HV hardness and 416.35 MPa UTS observed in the alloy was explained in the study of Huo et al. [9] that amalgamation of micro-voids like in Fig. 1a results in dimples having very close axes on tensile fracture surface normal to the direction of loading. The numbers of dislocations accumulate near large MgZn2 during subsequent plastic deformation (e.g., the dimples were ductile in texture with fracture in transgranular disorder).

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Fig. 1 Fracture surface of alloy A3 cast using cast with Al–5Zn–1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 100 °C for 15 h

Here, the surface was dominated by quasi-cleavage facets, only few dimples were observed. Basically, the presence of 39.63 wt.% O in the EDS spectra at the core of the fracture surface indicate the presence of microvoids and corroborates the dimples leading to the fracture of the sample. An earlier study Kazeem et al. [10] preliminary morpho-mechanical analysis had suggested the formation of phases like Al-Mg2 Si, AlMgZn, and MgZn as secondary particles. The sample which recorded hardness of 103.38 HV and 172.23 MPa following an artificial ageing at 120 °C for 15 h had tear ridges akin to the one observed in the other alloys. The prolonged ageing time of 15 h suggested minimal ductile dimples. Secondary phase particles get coarse at high temperature and elongated heat treatment time hence a drop their strengthening effect. The EDS spectrum (as obtained from Fig. 4c) reflected possible coarsening of particles like Al-Mg2 Si, AlMgZn, and Mg2 Ca in the presence of Si, Mg, and Zn. The presence of Ca, might generate sufficient stress concentration, which inhibits void nucleation and growth [10, 11]. It is the nucleation of voids that serve partly as failure sites which is detrimental to mechanical properties. Past studies had used SEM image similar to Fig. 2b to describe ductile dendrite suggesting coarse hcp-Zn grains. The tear ridges observed were further characterized to contain less dimples when compared to the dimples in Fig. 1c. The contours in Fig. 2a depicts mass pull of material during the tensile test. During solidification, secondary dendrite arm spacing of alloys decreases with increasing cooling rate. As the secondary dendrite arm spacing increases, the hardness, tensile strength, percentage elongation and impact energy of these alloys decrease [11].

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Fig. 2 Fracture surface from sample B2 cast with Al–4Zn–1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 120 °C for 6 h

Fig. 3 Fracture surface from sample B4 cast with Al–4.5Zn–1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 120 °C for 15 h

An assessment of the fracture surface of the alloy fabricated using 4.5 wt.% Zn after static tensile test is depicted in Fig. 3(a–c). Cracks are visible on the surface which is characterized by tear ridges. The failure commenced at a site occupied with microvoids at the peripheral circumference of the dog bone sample. This initiation point extended to from primary fracture point. Once the internal grains and lattice plane of the alloy was distorted, secondary cracks emerged using primary cracks as initiation point. An extended view of the fracture in Fig. 3b is characterized by ductile

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Fig. 4 Ultimate tensile strength (MPa) of samples after heat treatment a alloys aged using 100 °C, b alloys aged using 120 °C

dimples and bumpy surface demonstrating the ductility of the aluminum alloy. The detailed view the fracture surface characterized by the ductile tear ridges, transgranular ductile dimples. The transgranular manner of the crack depicts the direction of split within the fibrous appearance observed following the artificial ageing heat treatment of the sample at 120 °C for 15 h. A low energy fracture propagation mechanism was observed with some decohesion showing splitting occurred along the well-defined low-index crystallographic plane. The work of Becker [12] had identified such facture as weak along the cleavage plane. An extension of the fracture surface in Fig. 3c was assessed at the final stage towards the extreme of the final fracture zone of tensile tested specimen I the experimental 7xxx alloy [13]. Model of failure in the experimental alloys were predominantly propagated through microvoids nucleating and growing which gets distributed through large second phase particles. Apparently, the structure of the particles of secondary phases or precipitates plays an important role in the fracture behavior of the alloy [14]. When secondary phases are fine scale, it affects the energy absorption capacity of the material under tension, hence the yield strength and strain hardening resistance offered by the alloy [15].

3.2 Ultimate Tensile Strength The mechanical properties of the experimental alloys were measured by juxtaposing UTS (Fig. 4) with hardness (Fig. 5) as heat treatments and material composition were varied. The result suggest that heat treatment was more influential to the mechanical properties than the variation in the composition of the alloys. It should be mentioned that the sample (A3) fabricated using 5 wt.% Zn had the maximum UTS of 416.35 MPa following ageing at 100 °C for 15 h. The fracture characterization was

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Fig. 5 Hardness (HV) of samples after heat treatment a alloys aged using 100 °C, b alloys aged using 120 °C

with closed dimples and quasi-flat at the peripheral circumference before forming cup cone. The combination of 100 °C for 15 h offered a better UTS. In the category which 120 °C ageing temperature was used, the maximum UTS of 184.60 MPa was observed following the 10.5 h heat treatment in sample B7. The combination of 4.5 wt.% Zn and ageing at 10.5 h in B7 were responsible for the mechanical properties observed. The micro dimples observed in this alloy was space packed with the surface depicting weaker cohesion as against the one in A3. The room temperature tensile properties, in Fig. 4, of the alloys A1 (4 wt.% Zn), A5 (5 wt.% Zn), A6 (4 wt.% Zn) and A8 (5 wt.% Zn) were 225.57 MPa, 193.92 MPa, 182.97 MPa and 187.62 MPa respectively. The ageing temperature and time were maintained at 100 °C and 6 h, the discrepancies in the UTS are partly due to the variation in wt.% Zn. The result suggests that increase in wt.% Zn was beneficial to the UTS of the experimental alloys from RBCs. Further reported as a justification for the differences in the UTS of these alloys was the bounding and decohesion at the interface (precipitate/matrix) which may determine the mechanism responsible for deterioration of mechanical properties with time duration [16]. The wt.% of Zn was decreased from 5 wt.% in sample A3 to 4.5 wt.% in A4 and A7. Also, the ageing period were 10.5 h in both. The justification for maintaining a single ageing time was to investigate the effect of the decrease in wt.% Zn on the samples A3 and A7. The UTS for A4 and A7 alloys were 195.75 and 163.66 MPa apiece. When A3 (418.26 MPa) was compared with A7 (163.66 MPa), about 264 MPa increase in UTS was observed, a result of which was due to 0.5 wt.% Zn and 4.5 h increase in ageing period. Whereas, about 6 MPa difference in the tensile properties of theses alloys (in A4 and A7) can be attributed to the change in precipitation mechanism, morphology and distributions [17]. The results suggest that reduction in ageing temperature had more effect as against reduction in time in the alloy fabricated using RBCs. The above result is in agreement with Zaid et al. [18] who attributed the improvement in impact energy with retrogression times to the growth of equilibrium phases at grain boundaries, which

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improved the alloys stress corrosion cracking resistance during the heat treatment and maintained high strength. In the case of category B samples, a maximum UTS of 184.60 MPa was observed in alloy B7 (5 wt.% Zn) following artificial ageing at 120 °C for 10.5 h. The result further strengthened the earlier claim on the effect of increase in wt.% Zn on the mechanical properties of the experimental alloys when correlated with sample A3, an alloy fabricated with 5 wt.% Zn content. B1 was fabricated using 4.5 wt.% Zn, the alloy sustained an UTS of 178.26 MPa following ageing for 6 h. The reduction in the wt.% Zn from 4.5 wt.% Zn to 4 wt.% Zn in B2 was partly responsible for the decrease in the UTS wherein the alloy recorded 172.43 MPa. This property was akin to the B3 (172.23 MPa). The result showed that the effect of the increase in artificial ageing time from 6 h in B2 to 10.5 h in B3 had a negligible effect on the UTS of both alloys. Like in the sample B4 where ageing time was increased to 15 h, the prolonged ageing suggest increase in the grain boundaries and expansion of hardening precipitates lead to decohesion and weak ductile dimpled fracture with blown ridges like in Fig. 3. Alloys B5 (161.21 MPa), B6 (178.17 MPa) and B7 (184.60 MPa) were cast using 5 wt.% Zn, subjected to the same 120 °C ageing temperature, but B5 and B7 were aged for 10.5 h while B6 was for 15 h. The variation in time has no beneficial significance to the mechanical properties (UTS) of the alloys cast from RBCs. The fractographic analyses revealed the possible extension of network of ductile fracture which had steady disruption as holes in from of enlarged dimples were suddenly created which may be caused by defects like Zn vaporization or coarse precipitates (Fe, Si impurities) [19].

3.3 Hardness of the Alloy Alloys heat treated using 100 °C have hardness relatedly higher than the ones heat treated using 120 °C. For instance, 136.70 HV was the maximum hardness observed in A1, a property higher than the 107.00 HV in B1. Sample A3 with an UTS of 418.26 MPa had a hardness of 118.25 HV. The least hardness of 81.40 HV was obtained in sample A9 which had an UTS of 162.17 MPa. The result is in agreement with the report of Kilic et al. [20] wherein the hardness of the Al–Zn–Mg–Zr alloy was dependant on the formation of precipitate phases during quenching and also on the precipitates formed in an ageing sequence. Like reported in Curle [21], the 15 h ageing time used for the samples A9 and B9 was partly the reason for the low hardness as the normal precipitation sequence of supersaturation supported the formation of the MgZn2 . Extended ageing parameters leads first to a large increase in hardness until the phase transformation occurs, leading to decrease in the hardness. The result corresponded with the one observed in the UTS chart presented in Fig. 4. In the same manner, the patter observed in the UTS of alloys heat treated at 120 °C was repeated in the hardness plot presented in Fig. 6b. Suffice to note that the maximum hardness of 107.00 HV was recorded as the load bearing capacity of the alloy B1. The study conducted by Utami [22] had reported that hardness behaviour of 7xxx alloys were

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partly attributed to the formation of precipitation of coherent and finely dispersed MgZn2 phases serving as foreign atom or inclusion in the lattice of the host crystal (aluminium) in the solid solution during age hardening. The more distortions that occurred in the lattice, the harder the alloy. Extending this to the current study, it is suggested that sample A1(136 HV) had more of such distortions. Whereas the microstructure of A9 (91.41 HV) depicts enlarged boundaries like in Fig. 6c. The hardness observed in B2 and B3 were very close (about 103 HV each). Whereas B4 had 97.12 HV, B5 (96.76 HV) and B6 (95.48 HV) in that order. The reason for the observed trend in hardness and strength in the remaining samples is due to the variations in their grain size. At this point, a relative concentration of the phases, rather than loss of coherency, was suggested to decrease hardness upon overageing at 120 °C ageing temperature. The microstructure is depicted in Fig. 7. In the work of Gubicza et al. [23] increase in hardness was attributed to the change in GP zone- and/or the structure hardening formation alongside the coarsening of MgZn2 precipitates. This claim can be clarified, increase in the size of hardening particles with an unchanged volume fraction usually results in softening since in this case dislocations overcome the incoherent precipitates [24].

Fig. 6 Microstructure of alloy a A3 cast with Al–5Zn-1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 100 °C for 15 h. b B8 cast with Al–4Zn–1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 120 °C for 10.5 h

Fig. 7 Microstructure of alloy A9 cast with Al–4Zn–1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 100 °C for 15 h

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Fig. 8 Microstructure of alloys artificially aged at 120 °C for 10.6 h in alloy B5

3.4 Microstructure Study Microstructural assessment of the alloys revealed there are discrepancies as the time for ageing increases alongside the ageing temperature. The grey primary α-Al is common in all the microstructure with equiaxed morphology interwoven by bright intermetallic phases having various shapes such as the rod-like, round and agglomerated particles as shown in Fig. 8. This was well reported in Al–Zn alloys with corresponding EDS analysis [25]. The characterization of micropores was reported to be due to the casting process. The EDS analysis shows in addition to the primary α-Al phase Zn (4.29-5.66 wt.%) The irregular MgZn2 phase was distributed at grain boundaries [26]. The sample in Fig. 8a was for A3 cast with Al–5Zn–1.5 Mg–1.0Mn–0.35Cu, solution treated at 450 °C and artificial ageing at 100 °C for 15 h. There are α-Al intermetallic compounds seen to be dispersed in a homogenous manner with grain boundaries patterns of distribution of precipitates within the matrix. Grain boundaries were evidenced as the α-Al formed the alloy matrix. Course and elongated grains with MgZn2 precipitates were suggested to be present in grain boundaries.

4 Conclusions and Future Perspective This chapter consolidated on the previous findings done on novel Al–(4.00–5.00Zn)– 1.5 Mg–1.0Mn–0.35Cu by assessing the nature of fracture and correlate that with the mechanical properties of the cast alloys. The fractographic discrepancies were analyzed alongside het treatment parameters. From the experimental result, the following conclusions on 7xxx alloys are drawn;

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i.

Postmortem of fracture surface were characterized by quasi-cleavage, ductile dimples and cup cone morphology with hardening precipitates forming dislocations within the lattice of the Al-Zn alloy. ii. The UTS and hardness results were a reflection of the fracture surface as increase in heat treatment time was initially beneficial to the hardness. Further increase in the soaking period were detrimental to the hardness of the experimental alloys. iii. The alloy is suggested for aerospace seat frame, break lining, transmission system assembly and cylinder head applications in the aerospace and automobile industry. The experimental alloys can also be used as a source of primary aluminum alloy for experimental studies in laboratories. Acknowledgements Authors acknowledge Universiti Tun Hussein Onn Malaysia (UTHM), Universiti Teknologi Malaysia (UTM) and National Centre for Technology Management (NACETEM), Federal Ministry of Science Technology and Innovation (FMSTI), Nigeria for providing the facilities used in conducting this study for and also research collaborations

References 1. Singh RC, Ranganath MS, Saxena AK (2015) Investigation of wear behavior of aluminium alloy and comparison with pure investigation of wear behavior of aluminium alloy and comparison with pure aluminium. Int Conf Adv Res Innov ICARI-2015(3):305–314 2. Das S, Rana RS, Purohit R (2012) Reviews on the influences of alloying elements on the microstructure and mechanical properties of aluminum alloys and aluminum alloy composites. Int J Sci Res Publ 82(6):1703–1710. https://doi.org/10.1177/0040517512445340 3. Filho JWP (2016) Opportunities for aluminium components in automotive applications 4. Kazeem A, NurAzam B (2018) Industrializing Africa through aluminium alloys: the case of Australia, China and selected African Countries. In: Paper Present 8th African Unity Renaiss Conference Pretoria, South Africa, vol 1845(no 2), pp 46–54 5. Ochoa R, Flores A, Torres J, Escobedo J (2015) Manufacture of Al-Zn-Mg alloys using spent alkaline batteries and cans. Mater Today Proc 2(10):4971–4977. https://doi.org/10.1016/ j.matpr.2015.10.076 6. AlSaffar KA, Bdeir LMH (2008) Recycling of aluminum beverage cans. J Eng Technol 12(3):157–163 7. Juniarsih A, Oediyani S, Zain AP (2019) The effect of flux’s towards Mg reduction from aluminium beverage cans. IOP Conf Ser Mater Sci En. 478(1):1–7. https://doi.org/10.1088/ 1757-899X/478/1/012006 8. Dai P et al. (2019) Thermal stability analysis of a lightweight Al-Zn-Mg-Cu alloy by TEM and tensile tests. Mater Charact 153(9):271–283. https://doi.org/10.1016/j.matchar.2019.05.018 9. Huo WT, Shi JT, Hou LG, Zhang JS (2017) An improved thermo-mechanical treatment of high-strength Al–Zn–Mg–Cu alloy for effective grain refinement and ductility modification. J Mater Process Technol 239:303–314. https://doi.org/10.1016/j.jmatprotec.2016.08.027 10. Kazeem A, Rady MH, Ajala AJ, Badarulzaman NA, Fahmin W, Wan F (2019) Preliminary morpho-mechanical investigation of x7475 Al-alloys produced from recycled beverage can. Univers J Mech Eng 7(6):7–14. https://doi.org/10.13189/ujme.2019.071602 11. Lalpoor M, Eskin DG, Katgerman L (2008) Fracture behavior and mechanical properties of high strength aluminum alloys in the as-cast condition. Mater Sci Eng A 497(1–2):186–194. https://doi.org/10.1016/j.msea.2008.06.047

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Condition Monitoring of Wood Polymer Composite for Civil Engineering Nur Afiqah Sufian, Anika Zafiah Mohd Rus, Nurul Syamimi A. Salim, and Hendi Saryanto

1 Introduction For the past few decades, developments in Wood Polymer Composites (WPCs) have been increasing in terms of its application and market share [1]. Researches and studies are being conducted on this type of material due to its cost efficiency and the role it plays in decreasing the environmental impact. Generally, WPCs are composites which comprise of polymer matrix and natural fiber. The polymer matrix can either be virgin or waste plastics. Virgin plastic is plastic resin that has been newly created without any recycled materials. This type of plastic is produced either by using natural gas or crude oil, in order to create brand new plastic products for the very first time. Virgin plastic includes Polyethylene (PE), Terephthalate (PET), HighDensity Polyethylene (HDPE), Polyvinyl Chloride (PVC), Low-Density Polyethylene (LDPE), Polypropylene (PP) and Polystyrene or Styrofoam (PS). Plastic waste is the accumulation of plastic objects such as plastic bottles in the earth’s environment that have caused an adverse effect to the habitats and humans in this world. Meanwhile, natural fiber used in WPC composite as reinforcing materials are usually derived from renewable and carbon dioxide neutral resources such as wood or plants. Examples of natural fibers include softwood radiate pine, straw, RH, sawdust, cotton, jute, and wool. Today, common use of WPCs can be seen in the construction field. This far, WPCs is seen to be compatible for indoor and outdoor uses such as railings, fences, landscaping timbers, cladding and siding, park benches, molding and trim, N. A. Sufian · A. Z. M. Rus (B) · N. S. A. Salim · H. Saryanto Sustainable Polymer Engineering (SPEN-AMMC), Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, Batu Pahat, Johor, Malaysia e-mail: [email protected] H. Saryanto Mechanical Engineering Programme, Universitas Muhammadiyah Prof. Dr. HAMKA, JI. Tanah Merdeka No. 6, Pasar Rebo, Jakarta Timur, DKI Jakarta 13830, Indonesia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_6

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window and door frames, and indoor furniture. Rice husk and polypropylene based composites are among the types of WPCs which are gaining attention. Wood polymer composite is a composite which consists of wood and thermoset or thermoplastic. This material is still considered as a new material despite the fact that it is well known, and quite a number of researches have been conducted in the past several decades. However, it has only recently caught the attention of the wood plastic industry worldwide. During the early practise, inorganic fillers and reinforcements were used in the composite before wood is used as a substitution and recycled wood-chips or wood flour was utilized. The substitution exhibits several advantages such as lighter, less abrasive, renewable and low in cost. More importantly, this substitution improves the stiffness and dimensional stability with minimal weight increase. Due to unfamiliarity between the wood and plastic industry, the usage of wood plastic composites was limited before 1980 [2]. Furthermore, the lack of usage was also due to the fact that there were very few materials, equipment suppliers and different scales of various process materials. Wood polymer composite was first experimented in the industry as automotive interior which was manufactured by American Woodstock in 1983. Meanwhile, Italian extrusion technology was used to produce the WPC panel substrates where polypropylene with an approximate of 50% of wood flour flat sheets were extruded before forming them into various shapes [3]. Later, in the early 1990s, the Advanced Environmental Recycling Technology (AERT) together with a division from Mobil Chemical Company (Trex) started manufacturing solid wood polymer composites which consists of approximately 50% of wood fiber in polyethylene where they produced deck boards, landscape timbers, picnic tables and industrial flooring [3]. Today, the decking market is considered as the leading and fastest growing WPC market. The extruded WPC profiles have been manufactured and shaped straight into its final shape without having to go through milling process or further forming. Several companies have begun to venture into the manufacturing of WPC products which eventually leads to the market expansion. The market grew larger when several companies in the United States started providing feed stock from wood or other natural fibers and plastic (WPC compound) in pellet form to processors who were not capable or did not want to blend their own material. With the rapid development of technology and the increase of player in the market, the WPC industry increased radically. In 1991, the first International Conference on Wood-fiber Plastic Composites was held in Wisconsin, United States where ideas were discussed and cooperation took place between both researchers and industrial representatives [2]. Wood plastic composite as a substitute to plastic and steel components in the construction field is expected to increase in market growth due to a higher demand of low cost and more environment-friendly material. Wood polymer composites are still considered as a new material in the industry. Hence, there are several aspects that need to be taken into account to further utilize this material. Vigorous studies on WPCs are being conducted as its applications varies from structural to non-structural. Since WPCs are still considered as a new material, most producers are focusing more

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on how to improve the products in terms of processing, physical properties, aesthetic values and weathering effects. In general, the application of WPCs in replacement of other materials is predicted to be better. The aim of WPCs in outdoor application is its durability. Nevertheless, the knowledge of this product regarding its long-term efficiency is still vague. Wood polymer composites are a group of composites where natural fibers are combined with plastic materials by means of different kinds of plastic processing technologies. These materials are economical and have superior mechanical characteristics as compared to when synthetic fibers are utilised, depending on the differences of fibers densities [4]. Furthermore, the use of wood from agricultural by products (agro waste) and recycled polymer could assist with the environmental concerns. Lignocellulosic-plastic composites consist of semi crystalline plastics such as polypropylene (PP) and polyvinyl chloride (PVC). Thermoplastics with melt temperature below 200 °C are used due to limitation of natural fiber thermal stability. Polypropylene based composites application is mainly used in the automotive industry but recently, studies have been conducted to develop this material as building profiles [5]. WPCs have great number of advantages namely economical, sustainable and have a high material and mechanical characteristics. The key purpose of fillers usage in composites are to make it an economical and high strength material. Consequences in terms of environmental impacts on the resistance of fiber has been produced which has led to the rise of researches on the variation in the characteristics of WPCs when subjected to either artificial or outdoor weathering conditions. It is known that the addition of coupling agents can effectively control photo degradation of polymers. However, they are less effective when it comes to wood [6]. Due to the raise in commercial utilization of macromolecules, interest in the photo degradation of polymeric materials has been raising [7]. The impact of accelerated photo degradation correlates with the usage of RH into polymer composites due to the deterioration of fiber. Based on a forecast made by HOSUNG [8], wood plastic composite market in Asia Pacific is expected to experience significant increase of compound annual growth rate of 12.96% within the period of 2019 till 2027. The increase of demands in the mentioned region alongside the rise of new manufacturing processes and new recyclable raw materials are contributing to the market with prospects of potential growth. China shows prominent position of WPC application in the building and construction sector. Japan on the other hand are utilizing the use of WPC in the automotive industry by using plastic composites comprising of wood, straw, rice and several other materials to optimize the weight of cars and assist with carbon footprint reduction. Due to the increase of application in building and construction and automotive parts, WPC market in India is expected to have high compound annual growth rate [8]. As stated earlier, the applications of WPCs are increasing in various fields. Recently, quite a number of institutions and private sectors especially IBS industries in the Europe region have introduced a new policy of a more environment friendly products. Due to high demands, increase in production is needed. Polymers

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are known to be one of the contributing waste products in the world as it has wide applications in various fields. This leads mostly to the increasing effect on environmental impact. Some polymers are also derived from non-renewable source such as fossil fuels. The application of recycled polymer waste in WPCs might help in satisfying the demands on raw materials, decrease the environmental impact and increase the cost efficiency of the product. Previous studies have shown that the properties of recycled polymers have insignificant difference from virgin polymers due to their contents from previous process such as additives, coupling agents and so on.

2 Materials as Wood Polymer Composites for Civil Engineering Application 2.1 Structure and Properties of Polypropylene (PP) Polypropylene (PP) is widely used in various applications due to its good chemical resistance and weldability. PP is ideal for several packaging applications, car parts and outdoor furniture. PP has very high resistance to absorbing moisture and chemical compared to other wide range of bases and acids. Its resistance toward fatigue and impact strength is also high. On top of that, it is also tough, heat-resistant, and has ability to retain its shape after a lot of torsion, bending, or flexing. These entire characters make PP more favorable compared to other plastics because it is considered safe for humans. Unlike other plastics that contain bisphenol A (BPA) or other harmful chemicals, PP does not negatively affect human bodies and environment. According to Raymond et al., PP was first discovered in 1954 by Giulio Natta, followed by the polymerization of propylene monomer (Fig. 1) by Karl Ziegler, also in 1954. A new process for synthesizing polymers to produce a lot of common plastics, including HDPE and PP, was discovered by Ziegler and Natta. PP possess excellent chemical resistance and can be processed through many converting methods like injection molding and extrusion. PP is a polymer prepared catalytically from propylene. Its major advantage is its high temperature resistance [9]. There are about 10,000 to 20,000 units of monomer in the macromolecule of PP. Changes can occur in the steric arrangement of the methyl groups that are connected to every second carbon atom in the chain. When all the methyl groups are located on the same side of the winding spiral chain molecule produced a product known as isotactic PP (Fig. 2). If the methyl groups are connected to the polymer backbone chain in an alternating manner, it is known as syndiotactic PP (Fig. 3). Atactic form Fig. 1 Propylene monomer

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Fig. 2 Isotactic polypropylene

Fig. 3 Syndiotactic polypropylene

Fig. 4 Atactic polypropylene

of PP is when the structure of the methyl groups is attached in a random manner on the polymer back bone (Fig. 4). Atactic form of PP is when the structure of the methyl groups is attached in a random manner on the polymer back bone. However, isotactic PP is the only PP that possesses the required properties to be used as a plastic material. In order to polymerize PP in this form, stereospecific or Ziegler–Natta catalysts are to be applied. PP is also very well known as high-volume commodity plastic. Some of the advantages of PP are higher stiffness at lower density and higher temperature resistance when no mechanical stress is applied especially when compared to high and lowdensity Polyethylene. Apart from these, PP exhibits behaviors such as high resistance towards fatigue, environmental stress cracking, and detergent. Its extra good qualities include contact transparency, ease of machining and good process-ability by means of extrusion and injection moulding.

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2.2 Structure and Properties of Wood Wood contains natural polymers such as lignin, cellulose, and various hemicelluloses but has very different properties from the synthetic polymers with which it is most often combined. The efficient structure and anatomy make it a stiff, strong, tough, and lightweight material that can efficiently perform functions such as moisture transport that are critical for survival of the tree. Its excellent material performance and low cost have made it a useful structural material. The wood substance is a complex, three-dimensional, polymer composite made up primarily of cellulose, hemicellulose, and lignin. These three hydroxyl-containing polymers are distributed throughout the cell wall. The chemical compositions of selected woods of Cellulose varies the least in chemical structure of the three major components. It is a highly crystalline, linear polymer of anhydro glucose units with a degree of polymerization (n) around 10,000. It is the main component providing the wood’s strength and structural stability. Cellulose is typically 60–90% crystalline by weight and its crystal structure is a mixture of monoclinic and triclinic unit cells. Hemicelluloses are branched polymers composed of various 5- and 6-carbon sugars whose molecular weights are well below those of cellulose but which still contribute as a structural component of wood. Wood flour refers to wood reduced to finely divided particles approximating those of cereal flours in size, appearance, and texture. Wood flour comprises fiber bundles, rather than individual wood fibers, with aspect ratios typically only about 1– 5. Though the low aspect ratio limits the reinforcing ability, mechanical performance of the composite is sufficient for many applications. Common wood species are readily available due to its commercial importance. However, the properties of fibers and particles derived from wood can be significantly different from the the original wood. Methods for producing wood-derived fillers and fibers as well as the high temperatures and pressures often found during composite processing influence attributes such as surface chemistry, density, and moisture content of the wood component in the final composite. For example, wood fibers produced by thermomechanical means lead to lignin-rich surfaces while those produced by chemical means lead to carbohydrate-rich surfaces. Changes in surface chemistry, for example, can impact polymer adherence. The surface of wood undergoes photochemical degradation when exposed to UV radiation. This degradation takes place primarily in the lignin component and results in a characteristic color change. Mold can form on moist surfaces of WPCs. Although mold does not reduce the structural performance, it can be an important aesthetic issue.

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2.3 Rice Husk (RH) as Filler in Polymer Composites A polymer resin serves as the matrix for polymer composites, and one or more fillers are inserted to meet particular goals or specifications. Synthetic fibers, such as carbon or glass fibers, have traditionally been used to stabilize composites and can contain these properties. Their sluggish biodegradability, on the other hand, is a drawback in view of increasing global environmental issues. Natural fibres derived from industrial wastes are gaining prominence in the polymer industry due to various benefits such as light weight, low cost, and environmental friendliness. Rice husk (RH) is a natural sheath that develops around rice grains as they grow. As a raw fibre derived from agricultural and industrial waste, RH may be used as a filler in a variety of polymer matrices for composite materials. Based on the evidence obtained from previous studies, the use of RH filled composites as substitute building and construction materials is highly probable, with light weight and low cost being the main driving factors. Natural fibres have a lot of potential as reinforcing fillers in thermosets, thermoplastics, and elastomers because of this. Natural fibres have many benefits in composites, including low cost, sustainability, light weight, and nonabrasive and non-hazardous properties, as well as the ability to accelerate biodegradability of polymeric composites [10, 11]. Rice (Oryza sativa L., 2012) is a primary source of food for billions of people and one of the major crops in the world. It covers around 1% of the earth’s surface [12]. RH is a cellulose-based fibrous material with a wide range of aspect ratios [13]. Due to its high availability, low bulk density (90–150 kg m−3 ), toughness, abrasiveness in nature, resistance to weathering, and unique composition, a variety of applications have been proposed in the literature [14–16]. RH has the potential to be utilized as an insulating material, in the production of organic chemicals [17], panel boards and activated carbon [18], and supplementary cementing material [19]. Meanwhile, it has been stated that when RH is used to make composite plates, there is a poor interaction between the RH and the matrix components, resulting in poor particle–matrix adhesion [20]. While previous research indicated that RH particle board could be used to produce furniture and interior fittings, the particle board’s physical and mechanical properties were inferior to those of particle boards manufactured from wood particles [21–23]. The low aspect ratio and waxy/silica layer of the RH particles are the key reasons for the RH particle boards’ poor physical and mechanical properties [24]. The integration of RH into polymer matrices offers advantages such as biodegradability, light weight, durability, and weathering resistance, as well as making the finished goods more cost-effective [25, 26].

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3 Fabrication of Wood Polymer Composites, WPC Injection moulding is a manufacturing process where products are created by means of injecting molten material into a mould. Materials such as metal, glasses and thermoplastics can be used to be injected. This process works by feeding the material into the hopper where it is mixed together by screw inside the heated barrel. The material is later injected into the mould cavity and later cooled and hardened according to the shape of the cavity configured on the mould. Figure 5 shows the components of an injection moulding machine. The combined WPC and homopolymer pellets were poured into the injection moulding machine through the feed hopper. The injection moulding machine used was Nissei Screw Type Horizontal Injection Moulding NP7 Real Mini from Japan as shown in Fig. 6, with screw diameter of 19 mm and injection capacity of 14 cm3 . Table 1 shows the parameter set up for temperature zones at the injection moulding barrel section. The parameters set up were chosen based on the properties of the Polypropylene. The machine barrel temperatures which consist of five temperature zones were set as follow; the nozzle temperature was set at 195 °C, front and middle were set at 190 °C and 180 °C respectively, rear 2 and rear 1 were set at 170 °C and 175 °C respectively. The feeding temperature was set as constant at 50 °C. The temperatures set cannot exceed 200 °C because to avoid properties of RH from being affected. The injection rate and pressure were set at 50%. The injection time was set at 6.5 s while the cooling time which is the time after the material was being injected into the mold until the mold plates were opened was set at 40.0 s. An electromagnetic radiation with a range of wavelength from 10 to 400 nm is known as ultraviolet. In general, irradiation is a process where an object is being exposed to radiation. The radiation can come from various sources including natural ones. The term irradiation is usually referred to ionized radiation for a specific purpose. UV Accelerated Weatherometer Haida International Equipment Ltd. (Fig. 7) was used to irradiate the specimens. The UV accelerated weathering

Fig. 5 Machine components for injection moulding

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Fig. 6 Nissei screw type horizontal injection moulding NP7 Real Mini

Table 1 Parameters for temperature, pressure and velocity of injection moulding Parameter

Nozzle

Middle

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Rear 2

Feeds

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180 °C

190 °C

170 °C

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50 °C

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50%

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50%

Inject time

6.5 s

Cooling time

40.0 s

test was conducted according to ASTM D 4587-11 [27] Standard practice for fluorescent UV-condensation exposures of paint and related coatings. The UV irradiation from the UV weatherometer was carried out using an array of UV fluorescent lamps emitting light in the region from 280 to 320 nm with a tail extending to 400 nm.

4 Properties of Wood Polymer Composites, WPC For engineering applications, tensile tests were performed to obtain the tensile properties of materials. Tensile properties are important in determining how a material

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Fig. 7 UV accelerated weatherometer Haida International Equipment Ltd.

behaves when subjected to loading other than uniaxial tension. The main concern when it comes to material is its strength which is measured in terms of the stress needed to cause plastic deformation or the maximum stress value the material can endure. Other properties that are studied from conducting tensile tests are ductility and elasticity which are necessary in engineering design.

4.1 Condition Monitoring for Tensile Strength of Wood Polymer Composites Properties After UV Irradiation Exposure In general neat homopolymer polypropylene (HPP) specimen of C100 exhibits the highest tensile value compared to all other specimens. It is known that neat polypropylene consists of methyl groups which are attached to alternating carbon atoms on the chain backbone. This property resulted in better mechanical properties of the specimen, hence the specimen C100 showed better tensile strength than specimen A100 comprises of waste PP. Furthermore, in Fig. 8a–e showed the increased composition ratio of rice husk (RH) in the pellets effect the tensile stress. As the increment percentages of RH; B was increased from 20 to 60%, the tensile strength of specimen A60 B40 and A40 B60 decreased to 13.2063 MPa and 7.9688 MPa respectively. This could be due to the weak bonding between the RH filler and the polymer matrix. This weak bonding obstructs the stress propagation and thus, causes the tensile strength to decrease

30 20 10 0 20

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Fig. 8 Tensile stress of WPC specimens; a WPP, b A100 c A80 B20 , d A60 B40 , e A40 B60

when the load increases. In addition, poor dispersion causes agglomeration of the fillers as well as the decrease of tensile properties. As the composition of HPP increased in WPP specimens, the tensile strength decreased while waste polypropylene itself exhibits high tensile strength alongside HPP. However, when these two pellets were mixed and then blended together in injection moulding, the tensile strength of the specimens decreased. This is due to the incompatibility between these two pellets and their weak interfacial adhesion. Meanwhile, the addition of HPP as a mixture with the WPP containing RH resulted in the increase of tensile strength of the specimens. This increase of tensile strength with increase percentage of HPP was caused by more encapsulation of RH particles with neat HPP. This in turn resulted in the increased of stress distribution; hence better tensile strength. All the specimens were then subjected to UV irradiation exposure for 1000, 2000, 3000, 4000, 5000 and 6000 h. Specimen HPP100 in Fig. 9 still shows the highest tensile strength after UV irradiation. The decrease of tensile strength shown by this specimen was insignificant. From 33.7938 MPa, the tensile strength dropped to 31.4281 MPa after 6000 h of UV irradiation. The percentage difference between these two values is only 7%. Polypropylene (PP) in general is highly sensitive to degradation process when exposed to UV irradiation. As PP film is subjected to UV light, it undergoes photooxidative degradation. Despite the fact that pure PP eliminates the chromophoric groups responsible for UV ray absorption, it is not photostable. The existence of initiator residue and chromophoric groups produced during polymerization and processing at higher temperatures causes this activity. It usually absorbs a due to their additional fibres and fiber/matrix interfaces, which create additional pathways for moisture diffusion by debonding, they absorb more

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A100 A90 C10 A80 C20 A70 C30 A80 B20 A80 B20 C10 A80 B20 C20 A80 B20 C30 A60 B40 A60 B40 C10 A60 B40 C20 A60 B40 C30 A40 B60 A40 B60 C10 A40 B60 C20 A40 B60 C30 HPP100

UV Irradiation, Hours

Fig. 9 Tensile stress of WPCs after UV irradiation exposure

moisture. Figure 8a–e represent the tensile strength after UV irradiation exposure in details for each specimen. In general, the loss of mechanical properties of a polymer-based product occurs under the influence of processing conditions, or one or more environmental factors, such as heat, light, or exposure to chemicals. The tensile strength of A100 specimen (Fig. 9) experienced a significant dropped after 1000 h of UV irradiation because the composition itself was made from 100 wt% of WPP. WPP tends to lose its mechanical properties because the bonds within the material got more and more entangled when the material went through the recycling process. This entanglement replaced the original strength that the material possessed from the intermolecular forces within the atoms of the polymeric material. An optimum solution can be to blend the WPP with the HPP. This is in agreement with the research conducted by Raj et al. [28], which findings showed that after the third time of reprocessing, PP attained lower tensile properties compared to the first and second time. The decreases in the tensile properties of recycled PP were comparable with the tensile properties of virgin PP for specimen in which the first time re-processed material was used with virgin PP. It recorded maximum tensile strength when blended in 60:40 ratio, while for the second- and third-time reprocessed material, the best ratio to be used is 90:10. A40 B60 gives lowest tensile strength before experiencing UV irradiation exposure. The percentage difference between A40 B60 and A100 is 62.4%. The specimen continued to show lowest tensile strength after hours of UV irradiation exposure. This shows that this material is easily degraded subjected to weathering of UV irradiation exposure. Results obtained showed that adding HPP helps improves the tensile strength of the WPC specimens before and after being subjected to UV irradiation. Loses in tensile strength were still inevitable after UV irradiation but the decrease of values was insignificant. The percentage difference for specimen A80 B20 C30 after UV irradiation is 11.2%, unlike the percentage difference of specimen A80 B20 which

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is 34.4%. This clearly shows that the addition of HPP helps control the decrease of tensile strength after being subjected to UV irradiation exposure.

4.2 Modulus of Elasticity for Wood Polymer Composites Modulus of elasticity is one of the properties that can be obtained from tensile test. Modulus of elasticity (also known as Young’s modulus) is the measurement of a material’s resistance to elastic deformation when subjected to load. Figure 10 shows the Modulus of elasticity (MOE) of specimens before UV irradiation exposure. The result for modulus of elasticity before UV irradiation is as shown in Fig. 10. HPP100 exhibits lowest value for modulus of elasticity. The highest value of modulus of elasticity is exhibited by A40 B60 as compared to A100 as well as HPP100 clearly shows higher ductility. Lower MOE means that the material is more stretchable when subjected to force but contrary for high modulus elasticity materials. This is as expected because specimen HPP100 contain 100% HPP which exhibits high ductility and strength. Reprocessing of polymer is known to cause degradation through chain scission hence resulting in a lower viscosity of a material. This explains why specimen A100 shows higher modulus of elasticity. The material became stiffer after being reprocessed. This is supported by the work conducted by Elsheikh et al. [29], which investigated the effect of multiple injection moulding of copolymer PP on its mechanical stiffness and strength, melt viscosity, degradation response and molecular weight. The reprocessing of the material showed some effect on the material, where its molecular weight reduced by 10%, viscosity reduced by 11%, MOE decreased by 15% and flexural strength decreased by 11%. C100 A40 B60 C30 A40 B60 C20 A40 B60 C10 A40 B60 A60 B40 C30 A60 B40 C20 A60 B40 C10 A60 B40 A80 B20 C30 A80 B20 C20 A80 B20 C10 A80 B20 A70 C30 A80 C20 A90 C10 A100

0.01315753 0.195308646 0.270270922 0.284571126 0.69677157 0.382972673 0.437606372 0.49676595 0.586564383 0.338823901 0.33788621 0.368125501 0.40874178 0.323022505 0.315745673 0.450775157 0.440247837

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Numerous studies have shown that increasing the filler loading resulted in the increase of modulus of elasticity [30, 31]. RH filler is stiffer in nature compared to the WPP matrix. It deforms less which resulted in the decrease of matrix strain particularly in the surrounding particles as the result of filler and matrix interface. The modulus of elasticity gradually increased as the loading of RH filler in the composition increased. The modulus of elasticity of WPC specimen decreased at first when 20 wt% of RH fillers was introduced to the composition. This is due to the poor inter facial adhesion as mentioned previously. However, the MOE increased significantly to 0.5867 GPa and 0.697 GPa when filler loading was increased to 40% and 60%, respectively. This is in agreement with Fu et al. [31], which stated that increase of filler loading in the composition changes the material’s behaviour from ductile to brittle. The modulus of elasticity of WPCs specimens gradually decreased as HPP is added into the composition. The MOE of specimen WPP40 RH60 decreased from 0.6967 to 0.1953 GPa (specimen A40 B60 C30 ) after 30 wt% of neat HPP was added. The addition of HPP caused the matrix to increase in viscosity and increased the encapsulation of fillers in the composites, hence reducing the stiffness of the material. Specimen A40 B60 experienced largest decrease of MOE from 0.6967 to 0.3313 GPa after irradiation, which is about 52.4% reduction. Specimen A40 B60 C30 experienced much lesser percentage of MOE reduction, from 0.1953 to 0.1495 GPa, which is about 23.45% reduction. Similar pattern was detected in specimen A80 B20 and A80 B20 C10 where both experience reduction of MOE from 0.4087 to 0.2215 GPa (about 45.8%) and from 0.3681 GPa to 0.2825 (about 23.25%), respectively. Evidently from Fig. 11 that the specimens continued to show reduced MOE after hours of UV irradiation exposure. However, addition of HPP helps improves the MOE of the WPC specimens before and after being subjected to UV irradiation exposure, as explained above.

4.3 Flexural Properties of Wood Polymer Composites Figure 12 shows the result for flexural strength whereby the similar result of tensile strength for HPP100 showed highest value of flexural strength with 33.2 MPa. WPP40 RH60 recorded the lowest flexural strength of 12.4 MPa while WPC, A100 showed the highest flexural strength of 20.4 MPa, followed by A60 B40 at 17.3187 MPa, A80 B20 at 16.2563 MPa and A40 B60 at 12.4067 MPa. These three WPC with 60, 80 and 40% WPP attained lower flexural strength compared to A100 with 100% recycled PP. This could be caused by enhanced properties from the previous processes whereby materials that have been mixed with additives enhanced its flexural strength. A80 B20 shows lower flexural strength than that of A60 B40 because the composition of RH fillers as reinforcement was not enough for stress to be distributed evenly within the matric material. Addition of RH percentage in specimen doesn’t always improves the mechanical properties which is exhibited by specimen A40 B60 . However, addition

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35.3812 26.25 25.225 19.35 12.40627 25.56565 24.09375 22.33126 17.31873 24.675 22.33125 20.46873 16.25626667 24.7125 22.63127 21.3825 20.775 0

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of RH percentage in specimen doesn’t always improves the mechanical properties which is exhibited by specimen A40 B60 . This could be due to poor interaction between RH and matrix. As reported by Premalal et al. [32], one possible reason for this finding is the polar nature of RH and the nonpolar nature of the matrix. Increased RH content resulted in substantial filler accumulation, leading to weak stress transition from matrix to filler, resulting in poor properties.

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Figure 13 shows the flexural strength of WPC specimens after UV irradiation. As seen, the HPP100 shows the highest value of flexural strength before and after UV irradiation exposure. Initially, the flexural stress was 35.4 MPa but it decreased to 31.2 MPa after UV irradiation. The percentage difference between these two values is 11.9%. Before UV irradiation exposure or weathering simulation in the chamber, A40 B60 C30 showed flexural strength of 26.25 MPa which is the second highest after specimen HPP100 . However, after UV irradiation exposure, the flexural stress was dropped to 21.3 MPa. The percentage reduction of flexural strength is 18.92%. Meanwhile, it is noticed that the percentage reduction of A60 B40 C30 with higher recycled PP and lower RH content were recorded as 8.6% reduction from 25.56 to 23.3625 MPa. A80 B20 C30 recorded percentage reduction of flexural strength about 7.8%. It is obvious that the higher HPP content experienced less reduction in flexural strength and irrespective of percentage content of WPP, the UV irradiation exposure apparently caused a decrease in flexural strength. The percentage difference of flexural stress before and after UV irradiation for specimen A60 B40 C30 is 8.6% whereas the percentage difference for specimen A40 B60 C30 is 18.9%. This clearly shows that increasing the percentage of RH composition in WPC specimens does not help improves the mechanical properties after UV irradiation exposure or weathering. Increase of RH composition also means increase of lignocellulose. Higher percentage of this particular material causes more mechanical properties loss as lignocellulose is more prone towards photodegradation. This condition can also be observed through specimen A40 B60 which shows the lowest 40

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Fig. 14 Flexural modulus of WPC specimens before UV irradiation exposure

value of flexural stress before and after being exposed to UV irradiation which is 12.41 MPa and 8.9 MPa respectively. Figure 14 shows the flexural modulus of WPC which A60 B40 C30 shows the highest value of 1263.35 MPa obtained whereas WPP100 has the lowest flexural modulus (649.58). Initially, the WPC with RH and WPP composition (specimen A80 B20 and A60 B40 ) showed higher flexural modulus of 686.03 MPa and 891.05 MPa respectively compared to specimen WPP100 . The presence of RH in the composition which is stiff in nature leads to the restriction of polymer chains motion hence improving the stress distribution within the matrix phase. However, as the composition of RH was increased to 60%, the flexural modulus of specimen A40 B60 decreased to 655.26 MPa. This finding indicates that the mechanical properties of WPC specimens can be improved by increasing the filler loading up to 40 wt%. However, if increased further the WPC will become more brittle which leads to the decrease of flexural modulus shown by specimen A40 B60 . Addition of HPP helps improve the flexural modulus of WPC specimens tremendously. As mentioned earlier, specimen WPP60 RH40 HPP30 presented the optimum number of flexural modulus. Increasing the wt% of HPP increases the encapsulation of RH particles leading to the improvement of stress distribution within the matrix polymer. The flexural modulus of WPC decreased significantly as a result of moisture and ultraviolet radiation. This reaction caused the changes in crystallinity of the plastic matrix and oxidation on the surfaces of WPC. This mechanism is influenced by the encapsulation of RH particles in the matrix. This explanation is in good agreement with the flexural modulus shown by specimen A60 B40 C30 after 6000 h of UV irradiation. Hence, increasing the wt% of HPP helps reduce the losses of mechanical properties regardless of the type of matrix present in the composition. A40 B60 which has the lowest plastic content showed the lowest resistance against weathering. The incomplete encapsulation of RH particles leads to the increase of

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Fig. 15 Flexural modulus of specimens after UV irradiation exposure

mechanical losses. As studied by Te-Hsin et al. [33] and Lopez et al., it was reported that WPCs with plastic content of 40 wt% showed higher losses of mechanical properties after being subjected to weathering due to the laceration of polymer chains which caused fractures. This explanation is in good agreement with the flexural modulus shown by specimen A60 B40 C30 in Fig. 15. This leads to the diffusion of humidity through the WPCs surface which can instigate the formation of larger gaps between the phases. Thus, the increase in humidity outcomes in reduce of mechanical (tensile and flexural modulus) characteristics. The phase compatibility is affected by reactions caused by esterification. In addition, UV irradiation exposure causes the decline of crystallinity in plastic hence contributing to the mechanical losses.

4.4 Fourier Transform Infrared (FTIR) Infrared spectroscopy is a very well-known characterization method where the infrared spectrum of absorption or emission from specimen is obtained. FTIR is a method used to obtain the infrared spectrum in this study using the Perkin Elmer (Spectrum-100) spectrometer. The specimens were subjected to 20 scans between the frequencies ranging from 4000 to 600 cm−1 at a spectral resolution of 4 cm−1 and the Carbonyl Index (CI) of the specimens were calculated based on the absorbances at carbonyl group (–C=O) and methylene group (–CH2 ) [34, 35]. The carbonyl band was integrated between 1779 and 1680 cm−1 and the methylene between 2700 and 2750 cm−1 [35–37]. The calculation for carbonyl index is as shown in the equation below. Carbonyl Index, CI =

A1700−1900 A2916−2936

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Photooxidation and thermooxidation are two reactions that cause degradation to polymers. Both of these reactions lead to chain scission and cross-linking of polymers backbone, formation of carbonyl and vinyl groups hence changing the conformity and crystallinity of polymers. Carbonyl index which is obtained through FTIR analysis is used to calculate the rate of photodegradation encountered by WPCs in this study after UV irradiation. Lower percentage of CI indicates less degradation to polymers as compared to higher percentage of CI. From Fig. 16, A40B60 showed the highest percentage value of carbonyl index (CI) at 16.0366%. HPP100 and A100 showed insignificant difference in terms of CI while A100 showed slightly higher CI at 5.4655% compared to 4.5678% for HPP100 . This is due to the material of A100 which consisted of 100% of WPP. These results showed that higher RH content resulted with higher CI index, and WPP contributed to higher CI index compared to HPP. Introducing RH into the composition resulted in the increase of CI. At 20 wt% RH (specimen A80 B20 ), the CI obtained was 8.6623%. A60 B40 showed a CI value of 9.1968%. The CI increased significantly for A40 B60 with the highest CI. This is as expected as discussed earlier where increase of RH in the polymer composites means increase of lignocellulose. Higher amount of lignocellulose causes more mechanical properties loss as lignocellulose is more prone towards photodegradation. Thus, WPP contribute to higher CI by multiple processing changes the rheological properties by lowering the melt viscosity [38]. Lower melt viscosity of WPP indicated less roughness on particle surfaces and lower inter facial interaction between various particles in the matrix. A great loss in mechanical properties in WPP also took place which were caused by degradation during multiple extrusion process by a combination of thermal, mechanical and chemical degradation. Moreover, chain scission also occurred during reprocessing. The breakdown of a polymer’s main chain is referred to as chain scission in polymer chemistry. It is often caused by thermal stress. C100 A40 B60 C30 A40 B60 C20 A40 B60 C10 A40 B60 A60 B40 C30 A60 B40 C20 A60 B40 C10 A60 B40 A80 B20 C30 80 B20 C20 A80 B20 C10 A80 RH20 A70 C30 A80 C20 A90 C10 A100 0.0000

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Fig. 16 Carbonyl index (CI) of WPCs before UV irradiation exposure

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The effect of filler loading on CI was reduced by mixed blending the basic composition of WPC pellets with weight percentage of HPP. A60 B40 C30 showed the lowest value of CI at 4.55%. This is due to the encapsulation of RH fillers which made them less exposed to UV irradiation. This hinders the degradation went through by the specimen. The mixture of HPP with WPP however showed adverse effect. The mixture of these two types of PP resulted in poor interfacial adhesion which made the specimens more vulnerable when exposed to UV irradiation exposure. PP is known to be sensitive when exposed to UV irradiation. This phenomenon instigates photo-oxidative degradation when oxygen from surrounding is present. This leads to the formation of oxygen-comprised chemical groups that perform as chromophores which absorb UV radiation, hence increasing the rate of photo-oxidative processes. Figure 17 shows the CI value of WPCs after they were subjected to accelerated weathering. All of the specimens undergone photodegradation by the increase of CI value. The most prominent specimen that encountered photodegradation is specimen A60 B40 . The effect of photodegradation of wood fiber and PP matrix is doubled when filler loading is increased. Formation of chromophores build up after exposure that can be categorized as the induction period whereby the photo-oxidative degradation resulted in autocatalytic evolution. This contributed to the increase of CI value after WPCs were further exposed. Crystalline phase of PP matrix is affected after advanced weathering. Degradation took place at the amorphous region at first when exposed to UV irradiation which 30.0000

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then leads to the increase of crystalline phase in the material. The degradation of macromolecules in the amorphous phase resulted in the rearrangement of shorter chains which eventually become the new crystalline domains. When the PP matrix is compromised, the UV radiation later advanced towards the exposed RH fillers. When the matrix is affected, moisture and humidity are now capable to reach the RH fillers. Natural fibers generally have high affinity towards moisture and tends to swell during weathering. The exposure of RH fillers due to the degradation of PP matrix made them vulnerable towards the penetration of moisture. The RH fillers which initially acted as plasticizers within the polymer matrix is now weakened. This reduces the interfacial bonds of the RH fillers with the matrix which can generate and cause cracks propagation.

5 Correlation of the Mechanical Properties and Photodegradation of WPCs After UV Irradiation Exposure The fracture surface of specimens obtained during mechanical testing were analysed using Optical Microscopy (OM). The purpose of doing so is to study the correlation between the composition of WPCs and weathering effects on the mechanical properties obtained earlier. The morphology of fractures surfaces of WPCs specimens is used to corelate the mechanical properties obtained. In general, all WPC specimens’ fracture surfaces showed clean crack before subjected to UV irradiation exposure. A100 fracture surface showed clean crack in Fig. 18b after subjected to UV irradiation exposure as compared with Fig. 18a. However, as the time of exposure increased, formation of voids was noticeable on the surface. PP is known to have sensitive reaction towards UV irradiation hence photo-oxidative degradation is induced when oxygen originated from the surroundings is present. This will then lead to the acceleration of photo-oxidative processes

Formation of voids

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Fig. 18 Fracture surface of specimen A100 a before and b after 6000 h UV irradiation exposure

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from the formation of chemical groups consisting of oxygen that acts like UV irradiation absorbing chromophores. A research performed by Jansson et al. [39], showed that WPP is known to undergone degradation during the recycling process. The rate of photodegradation of the specimen was further induced after being exposed to accelerated weathering. The presence of voids on the fracture surface of WPC after UV irradiation indicates that adding HPP to the composition did not improved the mechanical characteristics of the specimens after UV irradiation exposure. It was noticed that for A70 C30 , voids started to show up after 2000 h of UV irradiation as in Fig. 19a. It was also noticeable that the size of the voids increased in size compared to A80 C20 in Fig. 19b which has less wt% of HPP. Meanwhile, a formation of slightly larger voids in Fig. 20 after 6000 h of UV irradiation compared to after 2000 h of UV irradiation. Unlike A100 after 6000 h irradiation, the fracture surface of A70 C30 showed a clean-cut fractured surface with no matrix pullover. This proves the poorer interfacial adhesion between the WPP and other ingredients in the specimen compared to HPP. However, increased of both wt% of HPP and WPP in the composition resulted with mechanical properties becomes weaker. Introducing RH particles into the composition by 20% did not helped with the improvement of the mechanical properties either. It can be seen that the RH particles in Fig. 21a for A80 B20 are poorly distributed. This poor distribution and low percentage of RH particles lead to less area coverage with reinforcements. Apart from that, the weak adhesion bond between the RH ingredients and WPP matrix contributed to the low mechanical properties. Adding HPP into the composition leads to more matrix pull-out. This is more apparent on the surface fracture of A80 B20 C30 as refer to Fig. 21b where the RH particles were covered by the matrix phase. Before being subjected to UV irradiation, the fracture surface showed an obvious image of matrix pull-out. A80 B20 C10 in Fig. 21c showed voids and breakage occurring on the surface of RH. Increasing wt% of HPP caused the RH particles to become more intact and less formation of voids. As the exposure hours of UV irradiation were increased, the RH particles in A80 B20 C10 were more pulled out. This is more apparent after 6000 h of

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Fig. 19 Fracture surface of a A70 C30 and b A80 C20 after 2000 h of UV irradiation exposure

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Fig. 20 Fracture surface of A70 C30 after 6000 h of UV irradiation exposure

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Fig. 21 Fracture surface of a A80 B20 , b A80 B20 C30 and c A80 B20 C10 before UV irradiation exposure

UV irradiation as shows in Fig. 22a, b. However, the pulling out of RH particles was reduced as wt% of HPP was increased as shown in A80 B20 C30 which HPP helped increase interface bonding of WPC with RH. As RH loading increased, the images of RH particles on the fractured surfaces become more apparent. For A60 B40 , before it was subjected to UV irradiation as in Fig. 23, the fractured surface showed clean crack on the RH particle. Pulling out of the fibres was insignificant. However, as the specimen started to be exposed to accelerated weathering, fibres pull-out become more apparent. Crack propagation on the RH particles can be seen clearly. After 6000 h of UV irradiation as in Fig. 24, the fracture surface of the specimen shows protruding RH particles. The presence of lignin in RH makes it very sensitive chromophores when exposed to UV. This reaction leads to the ignition of degradation processes alongside the formation of new chromophore groups consisting of carboxylic acids, quinones and hydroperoxyl radicals. Formation of gaseous compounds such as methanol, CO and CO2 from

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functional groups such as carbonyl, carboxy and methoxyl also takes place as the specimen gets further UV irradiated. Fig. 23 Fracture surface of A60 B40 before UV exposure

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Fig. 24 Fracture surface of A60 B40 after 6000 h of UV exposure

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A study conducted by Medupin and Abubakre [40], stated that the optimum reinforcement loading in WPC is at 40%. Increasing the fiber content leads to higher water uptake or absorption hence jeopardizing the mechanical properties of WPCs. Figure 25 shows the fracture surface of specimen A40 B60 before UV exposure. The fracture surface shows less pull out of the polypropylene matrix. The increase of fibre loading in the composition cause the RH particles to be the prominent substance. Applied stress is now distributed through the RH particles. The specimen becomes more brittle. RH being a natural fiber is not exempted from high affinity towards moisture. Exposure to UV irradiation and weathering leads to swelling which compromises the dimension of the specimen resulting in swelling stress alongside the formation of cracks which eventually advances to integrity failure. The presence of cracks allows moisture which acts as plasticizer to penetrate the recycled polypropylene matrix. This compromises the interfacial bond between the matrix and filler hence generating and induces more crack propagation. Figure 26 exhibits the fracture surface of specimen A40 B60 after 6000 h of UV exposure where the pulling out of the rice husk particles are more apparent.

Pull out of PP matrix

100 μm Fig. 25 Fracture surface of A40 B60 before UV irradiation exposure

Pull out of PP matrix

100 μm Fig. 26 Fracture surface of specimen A40 B60 after 6000 h of UV irradiation exposure

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6 Conclusion Swelling or shrinking of RH particles occurred within the PP matrices during cycles of water absorption and desorption. The difference between reversible dimensional changes of RH and plastic deformation of PP matrix causes internal tensions which leads to stress-induced damages of the interfacial bonds between RH particles with polymer matrix, pulling out RH fillers and voids formation. The existing voids are then filled with fillers during subsequent swelling which increased the interfacial tension. This repeated process alongside the combination of moisture and temperature effect and extended exposure resulted in the appearance of gaps along the RH particles which eventually leads to the increase of crack propagation. When subjected to weathering, the degradation takes place initially in the amorphous regions hence increasing the crystalline phase of the specimen. Domains of new crystalline appear developed through the rearrangements of shorter chains caused by degradation of macromolecules in the amorphous phase. As a result, the ability of the specimen to deform decreases while the tensile modulus increases. Acknowledgements The authors would like to thank the Ministry of Education Malaysia, University Tun Hussein Onn Malaysia (UTHM), Johor for supporting this research study under research grant vot K291.

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Synthetic, Hybrid and Natural Composite Fabrication Processes Onur Agma and Suleyman Basturk

1 Synthetic Composites Synthetic composites can be defined as artificially made composites. Chemically synthesized fibers/whiskers/particles/sheets are classified as inorganic or organic according to their content and are called synthetic reinforcement. The synthetic composites were named by using these synthetic reinforcement as composites [1]. For example, fiberglass fabrics, which are synthetic reinforcement materials in the first applications of composite materials, were used in secondary applications such as radomes in the aircraft industry. Moreover, the filament winding method with glass fiber was first used in the production of pressure vessels for “Polaris” missile engines as the primary application [2].

2 Natural Composites Natural composites can be termed as a type of composites which their reinforcing material made by natural ingredients. Especially these composites have been used since before the common era. For example, chopped straw and other vegetable matters were used for improving the structural performance of mud walls by the Israelites in B.C.E.1200 [2–4]. Examples of natural composites can be given as wood, bone, etc. It can be stated that wood is formed by the dispersion of strong and flexible cellulose O. Agma · S. Basturk (B) Mechanical Engineering Department, Engineering and Architecture Faculty, Altinbas University, Istanbul, Türkiye e-mail: [email protected] Electric, Autonomous and Unmanned Vehicles Application and Research Center (AUTONOM), Altinbas University, Istanbul, Türkiye © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_7

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fibers in the lignin matrix. The same information can be given as the presence of collagen in the hard and brittle hydroxyapatite structure of the bone [2, 3]. When we look at the usage areas of natural composites, it has been reported that they are used in the aerospace and automotive sectors. It stands out for the development of biodegradable and environmentally friendly materials, which are called green materials in both sectors. As can be observed in these applications, in natural composites; e.g.; adhesives can be used instead of thermoset composites [5].

3 Hybrid Composites Hybrid means a structure formed by the combination of two or more different elements. Hybrid composites can be defined as composite materials consisting of at least two different reinforcing materials embedded in the matrix material. Natural or synthetic reinforcing material can be used in hybrid composites. For example, glass fibers combined with natural fibers can be obtained at low cost, high specific strength and good electric insulation material [1]. For example, glass-based reinforcements (fibers) are inexpensive and lack of high mechanical properties. By using a glass-carbon reinforcement (fibers) hybrid composite, a mechanically stronger and more robust material can be produced at a lower cost [6]. Table 1 shows the classifications of fibers, which are commonly used reinforcement materials in composites. In hybrid composites, it may be a mixture of synthetic and natural fibers given in Table 1, and the mixture of fibers in these groups is considered as hybrid. Table 1 Some natural and synthetic fiber reinforcement materials [5, 7] Natural

Synthetic

Animal

Mineral

Cellulose/Lignocellulose

Organic

Inorganic

Silk

Asbestos

Bast

Aramid/Kevlar

Glass

Wool

Leaf

Polyethylene

Carbon

Hair

Seed

Aromatic Polyester

Boron

Fruit Wood Stalk Grass/Reeds

Silicon carbide

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4 Basic Manufacturing Steps For all composites, four basic manufacturing methods steps can be offered. These are impregnation, lay-up, consolidation and, solidification [8].

4.1 Impregnation In composite’s terminology, the terms impregnation or wetting are referred to as the process by which the reinforcement materials are wetted with resin. The purpose of this process is to obtain a structure with each reinforcing materials (e.g. filament) which are wetted with resin around. In this structure, since the matrix and fibermatrix combination play a very important role in the load transfer mechanism, correct impregnation is a key factor for composite materials [8]. Impregnation can be done differently at each composite manufacturing method. It is made during the manufacturing process in wet lay-up and wet-winding methods, while it is made during the prepreg manufacturing in dry lay-up and dry-winding processes. For example, in wet hand lay-up, the reinforcement material is located in a mold and the matrix material is impregnated with the help of a brush [8].

4.2 Lay-up Lay-up is the step in which the reinforcement materials are located according to the designated orientation. The structural performance of a composite part largely depends on the type of reinforcing material used, the number of layers, and its angle. Reinforcement placement methods are different from each other in each method [9]. For example, in filament winding, impregnated fibers are laid by the carrier unit along a predetermined path on the mandrel, usually in a computer-controlled manner. In hand laying, a certain number of layers of fabric are located at certain angles to achieve the desired lamina thickness. Apart from the above methods, there are also manufacturing methods in which short reinforcements are placed in random orientation and manufactured as isotropic composite parts. In addition, there are methods such as resin transfer molding in which the fibers are located in the mold in three dimensions [8].

4.3 Consolidation Consolidation is the process applied to remove excess resin and trapped air during composite fabrication. The aim is to manufacture the composite materials by reducing

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or eliminating the gap and void between the reinforcement and the matrix material [8]. For example, in hand lay-up, excess resin is eliminated by applying pressure with a roller. In addition, pressure is often applied for consolidation during curing. In processes such as filament winding, where the forces on the filament create sufficient consolidation pressure during production and no external influence is required, it occurs simultaneously during winding [8].

4.4 Solidification Solidification is the final step in composite manufacturing. In this step, chemical cross-linking of matrix materials takes place and accordingly the resin hardens and composites take their final shape. Generally, a positive pressure, vacuum and temperature are applied for the solidification. Curing time and pressure, vacuum and temperature requirements vary depending on the curing kinetics of the resin system [8]. For example, resins are often released by-products during the curing. It is necessary to remove them and apply different factors (e.g. vacuum) for a good consolidation. Similarly, some other resins can be cured at room temperature [8].

5 Composite Fabrication Process Composite fabrication process is the process of shaping the raw materials to become their final form. Some of the criteria which have to be considered while determining the fabrication method are as follows; size and shape of part, desired properties of the composites (mechanical strength, surface properties, etc.) production speed and manufacturing cost [1, 8]. Specially named production methods, which include the basic production steps mentioned above, in the literature will be introduced.

5.1 Wet Lay-up Processes Lay-up is the name of process for manufacturing the composite materials which reinforcement materials placed onto mold (open mold) with specific orientation. Lay-up is the general name for these methods, which hand lay-up and spray-up are specific examples, and their automation can be also possible. Hand lay-up is a widely used composite manufacturing technique and is one of the oldest techniques used in boat hull production in the middle of the last century. In this method, resins and reinforcement layers are manually applied one by one on mold

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Fig. 1 Schematic of hand lay-up process [11]

surface until the desired component thickness is achieved. Wet lay-up methods have certain steps as in other open mold methods such as cleaning the mold, applying release agent, applying thin gel coating (in order to obtain good surface quality), laying-up, curing and removing the part. After the process, depending on the mold, the product can be trimmed and machined [10]. Figure 1 shows schematically the hand lay-up process. Some examples about hand lay-up method usage of synthetic, natural and hybrid composites in the literature will be introduced. Hallonet et al. [12] produced the natural composite structures by wet lay-up method by using flax fibers and epoxy matrix. Li et al. [13] worked on wet lay-up method using synthetic reinforcements such as prepreg carbon and glass fiber with epoxy. As a hybrid composite, the use of oil palm (Elaeis guineensis) empty fruit bunch fibers in a polyester matrix together with glass fiber can be given as an example [14]. Spray-up method is an alternative of the release agent applying and laying-up steps. In hand lay-up step, each layer is applied by the roller, but in spray-up step after laying the fibers, each layer is formed using spray gun and pumping system for resin supply. In spray-up system chopping mechanism can be attached it, fibers are cut from this system and sprayed with resin. In spray-up methods matrix resins and catalyst hardener can be mixed with different methods. For example, internal and external mix with air, airless internal and external mix [10]. The schematic representation of the spray-up method is shown in Fig. 2. Automation can be done in both systems and with this feature, an increase in production speed can be achieved. In addition, automation can be done in order to increase the production quality. Figure 3 shows an example of an automated spray-up system. Natural, synthetic and hybrid composites can be manufactured by spray-up method. For example in the literature; Jute fiber was used to spray-up method to produce a natural composite [16]. Luchoo et al. [17] was used chopped carbon fiber in epoxy can be given as an example spray-up method for synthetic composite production. Pineapple leaf fiber and glass in vinyl ester was used as hybrid composite production in automatic spraying process [15].

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Fig. 2 Schematic of spray-up process [11]

Fig. 3 Automated spray-up system [15]

5.2 Prepreg Production and Vacuum Bagging (Prepreg Lay-up) Prepregs are material forms of reinforcing material that are pre-coated with uncured resin matrix material. Generally, continuous unidirectional or woven fibers are used in reinforcement materials [10, 18]. Prepregs are available in the form of rolls or sheets and ready for use in production. Hot melt or solvent impregnation are the

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Fig. 4 Schematic of prepreg production example [6]

most common methods in prepreg production. In the hot melt method, the resin film is impregnated into the fiber form reinforcement material using heat and pressure according to the desired weight formulation. For solvent impregnation, the fibers are passed through the resin solution, wetted fibers are calendered for obtaining the desired resin amount and then sent to the oven to remove the solvent. Prepreg production parameters (e.g. tack, drapeability) can be customized according to enduser requirements [6, 10]. The image given as an example of prepreg production is shown in Fig. 4. There are prepregs made from natural fibers which can be named as natural composite prepregs, wood-fiber which is sisal fiber, radiata pine thinning, slabwood in polypropylene (hot pressing) [19], hemp and kenaf fibers in acrylic resin [20], and pineapple leaf fiber in polylactic acid (PLA) [21]. Hybrid prepregs can also be obtained by using these natural fibers together, for example sisal and pineapple leaf in polylactic acid [21]. Prepregs produced with carbon fiber and epoxy, which are also supplied by industrial companies, can be given as examples of synthetic prepregs [22]. Hybrid prepregs in which Flax and carbon fiber are produced with epoxy are available in the literature [23]. Vacuum bagging (bag molding) is also called autoclave processing or prepreg layup. In this process, pre-impregnated reinforcement materials are cut, laid on the mold with the desired fiber angles and number of layers, and then vacuum bagged. Here, reinforcement materials can be cut first and then wetted with the matrix such as wet lay-up process. The wet reinforcement material is covered with a polymeric sheet. The sheet must be flexible and not stick to the laminate. Because of these properties, polyvinyl alcohol or polyamide (nylon) is usually chosen. Starting from the edges of the mold, it is completely covered. During the curing process, pressure is applied to the composite part by the plastic bag by vacuum. It can be called an autoclave process, since the autoclave is needed to heat the part, along with the pressure applied by the

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Fig. 5 Schematic and example of vacuum bagging process [11]

vacuum [8–10]. The schematic and example part of the vacuum bagging method is given in Fig. 5. Glass, aramid, carbon and basalt fabrics, which are called synthetic reinforcements in the literature about vacuum bagging, can be used with epoxy matrix. In the same article [24], it was used as a natural reinforcement in flax fabric and a hybrid composite example can be shown by using all of these fabrics together [24]. It has been reported that linen, flax and bamboo fabrics, which are natural reinforcement materials, can be used to produce natural composites in epoxy matrix with vacuum bagging [25]. Complicated shapes can be produced by vacuum bagging method. But it has low volume production capability. This process is very common in the different industries for making prototype parts. Wing structures, yacht parts, sporting goods can be produced by this method [1, 8, 10]. Complicated shape part manufacturing by vacuum bagging method is shown as an example in Fig. 6.

5.3 Pressure Bag Molding This method is very similar to vacuum bag molding, while the pressure applying system is different. As mentioned above, the vacuum created between the plastic bag and the composite part, but positive air pressure is applied in the pressure bag technique. Positive pressure is provided in this approach by blowing air into an elastomeric bag that covers the composite on the open mold surface. Pressure bag molding can also be done during the curing process of the wet layup and prepreg layup methods mentioned above. External heating can be added, or pressurized steam is blown onto the elastomeric bag instead of air pressure to expedite the curing process. Complex hollow components that ordinarily require cores and inserts are particularly well suited to pressure bag molding [10].

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Fig. 6 Composite car body. a) Reinforcement layup stage, b) vacuum bagging stage

Carbon fiber/epoxy prepregs can be given as an example for the fabricate of synthetic composites by the pressure bag molding method [26]. It is also stated in the literature that it can be used in hybrid and natural reinforced composites [27]. Figure 7 shows the schematic representation of the pressure bag molding method.

Fig. 7 Schematic of pressure bag molding [28]

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5.4 Filament Winding Filament winding is a convenient method in which a continuous reinforcement (fiber) or single yarns (mono filaments) are wrapped around a rotating mandrel and cured to manufacture hollow parts in closed form. In this method, during the preparation stage, the mandrel is manufactured with the desired properties and the mandrel is connected to the rotating shaft. Before the winding process, a release agent is usually applied to the mandrel, and the mandrel can be heated when necessary. The filaments are wound in repeating patterns around the mandrel. This wrapping completely covers the mandrel surface to form a complete layer. There are two types of winding, one of them and widely used one is wet winding in that fibers pass through a resin bath before the winding on the mandrel, other is dry winding which prepreg fibers are used. Curing for wet winding is usually carried out at elevated temperatures without the application of pressure. In the dry winding process, autoclave curing can be done. As the final step of the winding process, the mandrel is removed. Machining can be done to the produced parts, as well as surface mats or veils can be used at the end of the winding process [9, 10, 29]. An example schematic of the filament winding method is shown in Fig. 8. Lehtiniemi et al. [31] used flax fibers to produce cylindrical composite tubes by filament winding in bio-based epoxy. In this study, a drum-type impregnation system was used and natural composites can be produced by using a doctor blade for the removal of excess resin. Schematic of this system is shown in Fig. 9. In another study, it was reported that carbon, aramid and glass fibers, which are synthetic reinforcements, were produced by filament winding method in epoxy [32]. By combining the composite tubes produced with this method, hybrid composites (glass-carbon, aramid-glass, etc.) were produced. In another study, hybrid composite tubes were obtained by using kenaf and glass in epoxy resin [33].

Fig. 8 Schematic of wet filament winding process [30]

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Fig. 9 Drum-type impregnation unit for filament winding method [31]

Tape winding which may be directly related to filament winding, is a winding process in which it is wound on mandrel with continuous prepreg tapes. In this method, it can be done as parallel or angled winding. The key point of this method is that the orientation of the prepreg tapes is especially suitable for winding. Autoclave can be used to cure the parts after the end of winding process [8, 9]. It has been shown in this study that the pre-impregnated flax/PLA composite tapes are produced as natural composites by tape winding method [34]. In the literature, synthetic composites with carbon-epoxy and glass–epoxy prepregs can be produced by tape winding method [35, 36]. The schematic of tape winding and the production of natural composites with this method are shown in Fig. 10. The winding process can be provided by specially designed devices. These devices, which can have 6 axes (even 7 axes with robotic arm), can be computer controlled or different parameters can be controlled by the operator [10]. An example of a robotic filament winding machine is shown in Fig. 11. Parts that can be produced by filament winding are mostly curvilinear surfaces obtained by rotating them around a plane axis. Accordingly, the cross-sections of the produced parts are generally circular. It can also be produced asymmetrical parts in addition to these symmetrical parts. These products can be cylinders, pipes or tubes. The diameters of the parts produced by this method can be from a few centimeters to a meter [8, 10].

5.5 Pultrusion Pultrusion process, which are fibers or fabrics reinforcements are drawn from the resin matrix bath and then passed through the die, cured and cut to the desired length. The working mechanism of method is like extrusion process, except that material is pulled through the die in the pultrusion process not compressed into a die. During pultrusion, reinforcing material (fibers in the form of fabric or yarn) is passed through a matrix (resin) impregnation system. Excess resin is removed in the preform guides, then the fiber/resin system takes the desired shape and is taken into a heated mold

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Fig. 10 a) Schematic of tape winding, b) natural composite manufactured from tape winding [34]

and finalized with the curing system. After the production processes, the cutting can also be included in the system [1, 10]. Considering the pultrusion method for the production of synthetic composites, hollow rectangular, channel, wide flange profiles can be produced with glass fiber embedded in polyester resin [38]. Natural and hybrid composites can be produced by pultrusion method in hemp and wool polyester, polyurethane and vinyl ester resins [39]. Apart from this, in the literature; composites are produced by the pultrusion method by combining natural fiber jute fiber and synthetic glass fiber in polyester [40]. Pultrusion is a manufacturing process, which is a continuous, highly automated process that has high volume and quality. Some of the different shapes produced by this method are as follows; circular, rectangular, square, H or I shape. Non-linear and non-constant cross section parts can be produced [10]. The schematic of the pultrusion process is shown in Fig. 12.

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Fig. 11 Robotic filament winding [37]

Fig. 12 Schematic of pultrusion process [30]

Pullshaping, pullforming and pullwinding are special names as an application of pultrusion. Pullshaping method, pre-impregnated reinforcing materials are processed by passing through the pre-heating zone and then through the die part. Pullforming is a method in which the final product is obtained by shaping of partially uncured parts pulling through the molds which have different cross-sections. Pullwinding is a combination of traditional pultrusion and filament winding methods to produce composite tube [10].

5.6 Molding More special methods have been developed for molding processes in closed mold (matched die). In this section the details of these molding methods will be discussed.

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Compression Molding

Pre-impregnated reinforcements are positioned in the mold and composite production is made by closing with a reverse mold in compression molding. Premix products which are sheet molding compounds and bulk molding compounds are loaded into the press ready to be formed. Composite material is provided to take shape from flow in the mold, by applying mechanical pressure and temperature. Mostly, with the help of a pre-curing, the material is easily shaped in the mold. The parts manufactured by this method have mechanical properties such as high hardness and durability (tensile, compression, impact) and good surface properties (gloss, smoothness, paintability) [3, 10]. A schematic of all steps of the compression molding process is given in Fig. 13. In the literature, natural composites can be produced by compression molding method with differently oriented flax fabrics in soybean oil matrix [41]. In addition, composites can be produced by compression molding method using cellulose-based natural short fibers for which a review article has been written [42]. When viewed as a synthetic composite, chopped carbon fiber and glass fiber, their mixtures, are used in polymers such as PEEK, PEI, nylon, and PP. However, it can also be used as a prepreg tape in this method [43]. In the compression molding process, the “squeezing flow” phenomenon and the curing kinetics play a very important role. The squeezed flow determines the flow phenomenon of the resin due to the compression load when the mold is closed. The curing kinetics also varies depending on the closing speed of the mold and the rate of temperature increase [10].

Fig. 13 Schematic of compression molding process [30]

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Injection Molding

With injection molding, reinforcements are placed between the mold and the counter mold. The resin matrix is injected into the three-dimensional mold by pressure. The curing of the material takes place while the material is under pressure. In injection molding, the production rate of composites is high and generally the whole process is at a high level of automation. The filling of the mold can take place under high pressures in very short filling times (seconds) [10]. The schematic of injection molding is given in Fig. 14. Looking at the literature, it has been reported that wood fiber reinforcement with injection molding method can be produced with polypropylene (PP) matrix as an example of natural composite [44]. In the same study, synthetic composites can be produced by using chopped carbon and glass fibers in PP. Hybrid composite is obtained by combining this wood fiber and chopped synthetic fibers with any of them. It is written that chopped jute fiber as a natural composite is produced in polypropylene (PP) by this method [45]. As an example, in order to show the general use of this method; It is the injection molding of short fibers and/or fillers added into the resin. Although its applications are very wide, it is generally found in areas such as the automotive sector and consumer areas. However, screw extruder-style machines can be used to mix together with the matrix material, as the reinforcement materials become small pieces [10]. In the direct fiber feed injection molding (DFFIM) technology the reinforcing fibers are fed into the melt by the cutting and mixing action of the screw together with the plasticization process. It can be obtained containing longer fiber composites with this method. There are different parameters that control the composition of the composite. One of them is the number of reinforcements (fiber count), the others are to control the amount of matrix material by changing the screw speed, and the last is to change the rotation speed of the injection unit [47]. The visual representation of this method is shown in Fig. 15. Synthetic composites can be produced with glass fiber and carbon fiber reinforcements added to the polypropylene (PP) matrix, and even hybrid composites can be produced by using them together [47]. Hybrid composite can be produced by injection molding method by using thermoformed organosheet and glass fiber (continuous and short)-polypropylene mixture in polyamide66 matrix [48].

Fig. 14 Schematic of injection molding [46]

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Fig. 15 Direct fiber injection molding [47]

In the reinforced reaction injection molding (RRIM) process, two or more matrix resins are put together in the mixing chamber under high pressure. Reinforcements are added into the mixture and this resin matrix mixture is injected into a mold by high-pressure pumps or injection cylinders. Polymerization process can be carried out quickly in the mold cavity [30]. Figure 16 shows the schematic representation of the RRIM process. Fig. 16 Reinforced reaction injection molding [30]

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Fig. 17 Schematic of resin transfer molding process [30]

5.6.3

Resin Transfer Molding and Vacuum-Assisted Resin Transfer Molding

This method can be summarized as sending the resin into layers of fabric pre-placed inside the three-dimensional closed mold and leaving the composite material to solidify by creating an external pressure. Looking in detail; reinforcing materials in the form of fibers are brought into the desired form precisely with the help of cutters. After the cut reinforcements are placed in the mold (usually two pieces), the resin is sent to the mold. The resin is allowed to cure and the composites will be removed from the mold [10]. The schematic representation of the resin transfer molding method is shown in Fig. 17. In order to give examples of natural, synthetic and hybrid composites produced by the resin transfer method, when the literature is examined, it seems that sisal and glass fibers cut into polyester resin are added separately or by mixing [49–51]. One of the most widely used resin transfer method is the vacuum-assisted resin transfer molding. This method can be thought of as a combination of vacuum bagging method and resin transfer method. It is used to obtain a more homogeneous structure by taking support from the vacuum during the transfer of the resin. The homogeneous structure here; it is obtained by removing the excess matrix material from the system by means of vacuum [3, 4]. In fact, the schematic representation of the vacuum assisted resin transfer molding method, which also shows its similarity with the resin transfer molding method, is shown in Fig. 18. It has been reported in the literature that carbon and basalt fibers are used together with epoxy matrix as reinforcement in synthetic and hybrid composites produced by vacuum assisted resin transfer method [52]. It is mentioned in the literature that flax,

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Fig. 18 Schematic of vacuum assisted resin transfer molding

hemp and jute mixtures can be used with vacuum assisted resin transfer molding method [53]. It was presented in the same study that natural composite tanks were produced by using flax fibers in vinylester matrix. The resin transfer method is commonly used to develop small to large structures in medium volume applications. As an example of the pieces made by this method; aircraft spars, stiffeners and spacers, automotive panels and doors, windmill blades, helmets, bicycle frames and sports car bodies [1].

5.7 Thermoforming Thermoforming is the general name given to the process of shaping plastic parts using heat and pressure. Looking at the method, thermoplastic (heat-formable) sheets are placed horizontally on the surface of the mold and compressed using a device and the sheet is heated to the glass transition temperature using a heater. The thermoplastic sheet comes to a shape that can be shaped by the effect of heat and is then compressed to the mold surface by air pressure or any other suitable means. The softened sheet is deformed into the mold shape and is ejected after the mold is gradually cooled. The mold opens, and the thermoformed part is released [54, 55]. Schematics of thermoforming methods are shown in Fig. 19. Sheet thermoforming includes v-bending, matched-die forming, deep drawing methods. Pinus radiata fibers which are natural fibers in polypropylene are used in this method [56]. It is given in the literature that glass fiber is produced in polyamide6 matrix and long glass fiber is produced in polyamide66 as synthetic composite by thermoforming method [57]. The summary of the diaphragm forming process, which can be considered as one of the special methods of thermoforming, can be given as following. It is the shaping of the thermoplastic prepreg layers, which are freely between two diaphragms, against the female mold under the heat and pressure [55]. In a single diaphragm forming, the diaphragm is positioned on the upper surface of the material and force is applied, pressing the laminate to mold surface [58]. The schematic of the double diaphragm

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Fig. 19 Schematic of thermofing methods [56]

Fig. 20 Schematic of double diaphragm system [58]

method is shown in Fig. 20. With the help of this method, complex composite structures can be made [59]. It has been reported in the literature that the double diaphragm method is used in the manufacturing of carbon fiber polyamide6 (nylon) synthetic composite by using silex silicone sheet as the diaphragm material. Hybrid composite was obtained by adding tin sheet to the synthetic composite given in the same study [60].

5.8 Centrifugal Casting In centrifugal casting process, the composite matrix and reinforcements are manually placed into a hollow, cylindrical metal mold that is generally placed inside a furnace. It can be made by spraying the matrix material (resin and hardener) onto

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Fig. 21 Schematic of centrifugal casting process [30]

the reinforcement material while the mold is slowly rotating. Alternatively, the preimpregnated composite components can be cut and placed within the walls of the mold. For the curing process, the oven door is closed and the mold is heated and rotated at a higher speed. Before the solidification process begins centrifugal force evenly distributes and compresses the matrix and reinforcement to the inner walls. Then the mold is stopped, and the part is removed, and the composite is obtained. Generally good surfaces (both interior and exterior) are obtained [10]. The schematic of the centrifugal casting method is given in Fig. 21. In the centrifugal casting method, the reinforcement materials, which are mostly in the form of particles, are used in the matrix material. When we look at the literature, examples of synthetic and hybrid composites can be given as copper, ferrite, graphite powders in epoxy resin, separately or as a mixture of them [61].

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Application of Composite for Engineering Application Muhammad Zuhair Mohd Abdul Rahman, Ahmad Hamdan Ariffin, Syariful Syafiq Shamsudin, Mohamad Norani Mansur, Mohammad Sukri Mustapa, and Abdul Rahim Irfan

1 Introduction This chapter will review the origins and applications of composite materials. The focus of the discussion is on the mechanical properties of pineapple leaf and kenaf fibres, which could serve as a viable alternative to non-biodegradable sources when petroleum reserves diminish. When a product approaches the end of its useful life or cycle, natural fibres can be recycled without damaging or polluting the environment because they are biodegradable. Additionally, a more eco-friendly product can be created, and agricultural waste, particularly pineapple leaves, can be reduced. Composites have been used for a variety of purposes in daily life, including transportation components, building materials, and appliance components. The incorporation of composites facilitates the production of lightweight and durable materials.

M. Z. M. A. Rahman · A. H. Ariffin (B) · S. S. Shamsudin (B) Research Centre for Unmanned Vehicle (ReCUV), Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia e-mail: [email protected] S. S. Shamsudin e-mail: [email protected] M. Z. M. A. Rahman · A. H. Ariffin · S. S. Shamsudin · M. N. Mansur · M. S. Mustapa Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia A. R. Irfan Faculty of Mechanical Engineering Technology, Universiti Malaysia Perlis, Kampus Tetap Pauh Putra, 02600 Arau, Perlis, Malaysia A. H. Ariffin · A. R. Irfan Green Design and Manufacture Research Group, Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Universiti Malaysia Perlis, 01000 Kangar, Perlis, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_8

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The applications of composites in cars will be highlighted, as they are widely used in our daily lives.

2 Composites in Industries Composite materials comprise two or more components having different physical and chemical properties, resulting in a new material with different characteristics than the original. Composite materials, like other materials, offer benefits such as high strength and stiffness, as well as the capacity to produce lightweight materials. The composite manufacturing method was versatile, efficient, and high-tech [1, 2]. Composites were first used around 1500 B.C. when the early Egyptians and Mesopotamian pilgrims used a combination of mud and straw to make solid and sturdy structures. The first composite bow was invented by the Mongols around 1200 AD. The resulting bows were both powerful and precise. During World War II, many composite materials were developed and advanced from the laboratory to mass production [3, 4]. Fibreglass composites were swiftly embraced for shielding electronic radar equipment after it was discovered that they were straightforward to work with when it came to radio frequencies. Composites were utilised to build boats after that, and the first business boat structure was unveiled in 1946. In the 1950s, composite materials were widely used in the marine industry. In the late 1970s and early 1980s, Asia and Europe were the first to use composites in infrastructure. Composite enterprises began to expand as better plastic sap and improved strand building techniques were available [3, 4]. The four categories of fibre-reinforced composites described by their matrices are metal matrix composites (MMCs), ceramic matrix composites (CMCs), carbon/carbon composites (C/C), and polymer matrix composites (PMCs) or polymeric composites [5]. In the future, the advancement of composites in industry will improve the properties of composites, offering a more extensive scope of utilisation. Composites are on the way towards being more harmless to the ecosystem. Composites will keep on making the world more grounded, lighter, and more robust.

3 The Application of Composites Composite materials have been utilised in high-performance aircraft components such as tails, wings, fuselages, and propellers. In addition, composite construction materials such as concrete, reinforced plastics, cement, steel-reinforced concrete, and composite timber beams are utilised to increase the resilience of a structure. Moreover, composites were also used to reinforce the structure of the transport vehicle. The body of the vehicle can be composed of composite material to reduce its weight and thus further improve fuel consumption [6].

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3.1 Infrastructure There is a need for stronger materials to support modern high-rise buildings. The use of cement in concrete to increase the tensile strength of buildings has increased in recent years. Wood and other unstable materials may cause the building to collapse. Due to its high compressive strength and low tensile strength, concrete is utilised extensively today. Concrete is fragile and prone to cracking when it fails. Therefore, fibres have been incorporated into cementitious materials to make them harder and more durable [7]. During construction, many resources will be utilised, particularly non-renewable resources such as oil and numerous other minerals [8]. In order to strengthen houses and tall buildings, concrete and reinforcing bars are employed [9]. Recently, macro synthetic fibres have been added to concrete to avoid brittle failure [10]. By using eco-friendly materials, it is possible to simultaneously reduce pollution and increase the building’s durability.

3.2 Transportation Humans used to travel solely by foot before having access to any other modes of transportation. Humans began using animals for transportation between 4000 and 3000 years ago. At around 3100 B.C., Egypt developed the sailing ship and Rome constructed a network of roads throughout Europe. Iraqis invented wooden wheels in the 3500s BCE, according to historians. There were three modes of transportation currently available: i.e., through air, ground, and sea. The way people use various modes of transportation is influenced by their cost, accessibility, and availability. As with any mode of transportation, there are advantages and disadvantages to each transport mode [11].

3.2.1

Air

A vehicle that can travel through the air despite being heavier than the air is referred to as an air vehicle. It can propel itself through the airflow. The advantages of the air vehicle include the ability to travel over greater distances and at a faster rate. Due to the vastness of the earth’s atmosphere, air vehicles can avoid congestion while having a minimal impact on air pollution [12]. The Wright brothers conducted a programme of aeronautical research and experimentation between 1899 and 1905, which resulted in the first successful powered aircraft in 1903. Wilbur and Orville Wright were recognised in 1904 as the inventors and pioneers of flight, following many attempts. Shortly afterward, they constructed and flew the first fully functional aircraft, achieving the first powered, continuous, and

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controlled flight. Since then, all successful aircraft have incorporated the fundamental design elements used in the Wright brothers’ design [13, 14]. Although fibre-reinforced plastic was first used in aircraft in 1939, its widespread adoption did not occur until the 1960s. Modern aircraft utilise carbon fibre reinforced polymer (CFRP) [15]. The benefits of composite materials include lower material costs, less weight and greater strength, radar stealth, and the ability to make streamlined shapes that are impossible to produce with wood or metal [16].

3.2.2

Road

The most common and important mode of logistics transportation is the road. Road transportation has been around longer than any other mode of logistics and is utilised the most, from walking to horses to waggons to bicycles to cars to trucks. Thanks to continual advancements in vehicles and road infrastructure, road transit is the most versatile of the four main modes of transportation, with the fewest geographical limitations. This characteristic of vehicle transport makes it suitable for conveying smaller loads over shorter distances, and it is the only mode capable of delivering goods door-to-door [17]. The land vehicle gives mobility for people to move in the local area. This is because of the ability of a land vehicle to pass through remote areas. Even though land vehicles are easier to access, the pollution of land vehicles varies depending on how the vehicle has been used. The modelling and planning on the usage of the land vehicle are important because more pollution will happen if the vehicle is heavier, which will cause more fuel to be burnt to support the usage of the vehicle [18].

3.2.3

Maritime

In the late 1940s, composites were first used to construct boats. This boat has a high level of durability, design flexibility, impact resistance, and corrosion resistance. Prior to its construction with composites, the boat was made of wood. The vessel utilises sails to explore the continent. In the 1800s, sails were replaced with steam engines as a means of propulsion. A water vehicle gives mobility for movement on the water. Air transport and water transport have the same advantages. Water transport has fewer traffic issues due to the vast ocean. The use of water vehicles was less because the risk was higher for travel in the ocean. The travel route for water transport is longer than for air vehicles. Therefore, water transport adds the least pollution to the air. [12].

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4 Material in Automobile Industry Material selection in the automotive industry depends on the demand from customers’ expectations and legal requirements. Materials such as aluminium, steel, magnesium, composites, and plastics have been used all over the car. Most of the car accessories, such as floors, hoods, and compartment covers, use composites, which have a high strength-to-weight ratio with good stiffness. This makes the car lighter and conserves fuel. The materials that have been used on body panels, doors, and bumpers currently used are strong and stiff. The material was also required to have corrosion resistance as it was positioned on the outer of the vehicle [19]. Figure 1 shows the component that uses plastics and composites in automotive. Figure 1 shows the components that use plastics and composites in automotive vehicles. The development of current materials enables the use of lightweight vehicles that have strong metal. The percentage of plastic usage has increased from 6% in 1970 up to 18% in 2020, while metal usage has decreased almost 20% compared to this change. Even though the steel usage decreases over time, the materials that replace Automotive Components (plastics & composites)

Under the hood

Exterior

Interior

Bumper and fender

Instrument panel

Crash structures

Head/ rear light housing and lenses

Door panels

Leaf spring

wheel cover

A and B pillar covers

Fuel system

Trim

Seats

Manifold

Fig. 1 Automotive components that uses plastic and composites [20]

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Table 1 Properties of material used [23] Material

Density (km/m3 )

Young’s modulus (GPa)

Poisson’s ratio

Aluminium B390 alloy

2710

81.3

0.33

Mild steel

7800

210

0.3

Glass mat thermoplastic

4900

69

0.39

the steel still meet the requirements for the strength and structural performance of the vehicle. The bumpers, which will be the initial point of contact in the event of a collision, are one of the most important parts of a vehicle. Steel is utilised in modern bumpers due to its resistance to impact, corrosion, strength, and stiffness. Several materials have been investigated in an effort to enhance impact absorption and reduce their costs. Because the bumper is exposed outside of the vehicle, it must be more durable and have a longer lifespan, as exposure may cause it to degrade more rapidly [21]. Recent studies have demonstrated the use of hemp fibre and glass fibre as reinforcements. The properties of hybridised glass fibre and hemp surpass those of glass fibre reinforced epoxy. The hybridization process makes the bumper lighter and biodegradable. As the hybrid strengthens the bond and properties of the material, the hybrid’s absorption increases [22]. In the previous study, several materials were replaced to improve the bumper. In order to compare materials such as aluminium B390, mild steel, and glass mat, simulation testing has been conducted. Tables 1, 2, and 3 display the data that was analysed using a simulation.

5 Fibres of Composites A composite can be constructed from synthetic fibre, natural fibre, or hybrid fibre, that also combines two fibre types. Natural fibre and synthetic fibre each have their own classifications and properties that can be utilised in a variety of contexts [24]. The classification of natural and synthetic fibres is illustrated in Fig. 2. Synthetic fibre has received a lot of attention in the previous two decades. Synthetic fibre-reinforced polymer composites have high strength and stiffness, but due to their non-biodegradable nature, synthetic fibre disintegration is detrimental to the environment [26]. Synthetic fibres include nylon, polyester, and acrylic. The synthetic fibre was made using a melt-spinning or heat-setting approach. Synthetic fibre is more durable than most natural fibres. Synthetic fibre has features such as stretch, watertightness, and strain resistance [27]. Nylons are made from coal, water, and air, and due to their flexibility, they are widely used in seatbelts, socks, and rock-climbing ropes, as well as nets. Natural fibres have low water resistance, durability, and fibre/matrix interfacial bonding, resulting in a loss of final composite properties and limiting their industrial

35

Glass mat thermoplastic

82

4

2

Mild steel 146

6 141.9

150.3

148.5

8

6

Aluminium B390 alloy

12

40 km/h (MPa)

60 km/h (mm)

40 km/h (mm)

80 km/h (mm)

Stress analysis

Speed

Static deformation

Material

Table 2 Mechanical analysis of material on static [23]

276.1

224.7

224.4

60 km/h (MPa)

435.9

298.7

302.0

80 km/h (MPa)

60 km/h (mm) 1.31e−3 6.851e−4 1.638e−2

40 km/h (mm) 1.208 e−3 4.551e−4 8.368e−3

Static analysis

2.744e−2

9.197e−4

2.465e−3

80 km/h (mm)

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13.5

Glass mat thermoplastic

20.5

15.7

105

Mild steel 27.0

21.0 91.7

776.5

508.1

28.25

14

Aluminium B390 alloy

35.5

40 km/h (MPa)

60 km/h (mm)

40 km/h (mm)

80 km/h (mm)

Stress analysis

Speed

Static deformation

Material

Table 3 Mechanical analysis of material on impact [23]

133.3

1150.2

753.9

60 km/h (MPa)

172.1

1530.8

1110.3

80 km/h (MPa)

60 km/h (mm) 5.591e−3 3.743e−3 7.273e−3

40 km/h (mm) 3.633e−3 2.528e−3 5.075e−3

Static analysis

1.007e−2

4.968e−4

8.305e−3

80 km/h (mm)

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Fibre

Natural

Animal

Synthethic

Inorganic

Organic Fibre

Mineral Cellulose/ lignocellulos

Fig. 2 Classification of natural and synthetic fibres [25]

usage [28, 29]. Fibre crops have existed from the beginning of time. Natural fibre reinforced composites include hemp, flax, coir, sisal, banana, pineapple, and bamboo. Reinforcing substances and an epoxy or polymer matrix make up the structure. Natural fibre composites have worse environmental sustainability characteristics than synthetic fibre composites [30]. Table 4 shows the strength limit of some natural fibre that can be used as a composite reinforcing agent. Since the beginning of time, natural fibres have been used for shelter and clothing, but their use has decreased since the invention of synthetic fibres. However, the depletion of natural resources such as petroleum has increased the importance of natural fibres, prompting researchers and industries to propose and use them in place of synthetic fibres [28]. Moreover, natural fibre has an advantage over synthetic fibre Table 4 The comparison analysis of natural fibre characteristic [31–35] Properties

Density (g/cm3 )

Tensile strength (MPa)

Young’s Modulus (GPa)

Elongation at break (%)

Jute

1.3–1.46

393–800

10–30

1.16–1.8

Flax

0.6–1.5

345–2000

12–80

1.2–3.2

Pineapple

0.8–1.6

400–627

1.44

14.5

Bamboo

1.25

140–230

11–17

–

Sisal

1.33–1.5

400–700

9.0–38.0

2.0–14

Hemp

1.48

550–900

70

1.6–4

Coir

1.2

175–220

4–6

15–30

Kenaf

1.5

930

53

1.6

Ramie

1.5

220–938

44–128

2.5–3.8

Cotton

1.5–1.6

287–597

5.5–12.6

3–10

E-glass

2.5

2000–3500

70

2.5–3.0

S-glass

2.5

4570

86

2.5–2.8

Aramid

1.4

3000–3150

63–67

3.3–3.7

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Table 5 Comparison between natural and synthetic fibres [37] Aspects

Property

Natural fibres

Synthetic fibres

Technical

Mechanical properties

Moderate

High

Moisture sensitivity

High

Low

Thermal sensitivity

High

Low

Resource

Infinite

Limited

Production

Low

High

Recyclability

Good

Moderate

Environmental

in terms of biodegradability [36]. Table 5 compares the characteristics of natural fibres.

5.1 Hybrid of Composites Fibres Multiple fibre types can be combined to create hybrid fibres. The strength of the fibre can be increased by combining synthetic and hybrid fibres, but the nonbiodegradability nature of synthetic fibres will remain. Increasing the biodegradability of composites is a step that can be taken to help protect the environment. To create an effective composite laminate, it is necessary to determine how many layers are required as well as the orientation and thickness of each layer’s fibres. It is advantageous that composite materials have good mechanical properties. However, in order to take advantage of this benefit, it is necessary to optimise the form and size of the material, as well as determine the optimal arrangement of fibres within the material. This presents an excellent opportunity to change the properties of the material, but it also makes the design problem more complicated. This problem arises not only as a result of the substantial number of design variables, but also as a result of the multimodal, variable-dimensional, and expensive or inaccessible derivatives of the optimization problem [38, 39]. In recent years, there has been a growing interest in combining two or more fillers into a single matrix. From 2013 to 2018, many nations throughout the world focused on developing composite hybridisation research. Figure 3 depicts the top ten countries that conduct the most hybrid composites research. China has led the way in hybrid composite research, with India and the United States following behind [40].

5.2 Hybridisation of Natural and Synthetic Fibre Hybridisation of natural and synthetic fibres has a similar goal of improving material qualities, and one example of this hybridisation is the development of body armour

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3.1% 3.1% 3.1% 3.5%

China India

4.4%

USA

4.5%

South Korea 45.9%

7.5%

Germany Iran Japan Malaysia

12.0%

Australia 13.0%

Italy

Fig. 3 Contribution of counties in hybrid composites [40]

[41]. Synthetic materials excel at corrosion resistance, strength, and impact resistance. Several methods, such as the Analytical Hierarchy Process (AHP), can be used, and testing should be done according to the analytical requirements [38, 42]. Natural fibres are being studied as a possible replacement or addition to composite materials in an attempt to improve their properties. Changing a certain proportion can improve the material’s properties by a small or significant amount compared to using only natural fibres. It is possible to reduce the use of synthetic fibres by incorporating natural fibres, which have been studied and tested in previous research [38, 39, 43, 44]. Table 6 summarises the research findings of several natural and synthetic fibre hybrids. Included for comparison are the best materials for each investigation and the results of each experiment.

5.3 Hybridisation with Synthetic Fibres Humans produce synthetic fibres such as carbon fibre and glass fibre. For instance, Barjasteh et al. [52] studied the thermal ageing of carbon fibre and fibre glass hybrid composites. The purpose of this study was to determine the kinetic thermal oxidation and damage mechanisms of the composite. To determine the oxygen concentration profiles and thickness of the oxidised layer, a model was applied to the thermal oxidation of the hybrid [52]. Additional research has been conducted on glass and Kevlar fibre, the first of which focuses on hybrid fabrics composed of glass and Kevlar fibre. Hybrid strand composite and hybrid fabric composite were the two conditions used in the study by Dos Santos Felipe et al. [53]. The hybrid strand composite laminate demonstrated greater tensile strength, whereas the hybrid fabric composite laminate demonstrated superior properties in a three-point bending test, such as a

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Table 6 Data for best material selection for each research Best material

Impact data

Maximum flexural stress (MPa)

Maximum tensile stress

Analysis based on different sequence

Kevlar–Cocos Nucifera Sheath [43]

Increases impact energy dissipation

175

Decreases slightly

Yes

Carbon–Flax [39]

–

213.7

309.69 MPa

Yes

X-ray Film [41]

4 bar pressure to penetrate

150.71

–

–

Fibre Glass–Jute–Kenaf [45]

Highest impact resistance

–

73.63 MPa

–

Coconut Sheath [46]

–

–

196 MPa

–

Kenaf bast [42, 47]

–

–

295–930 MPa

–

Kevlar–Basalt [48]

–

188

174 MPa

–

Kevlar–Oil Palm EFB [49]

–

66.9

33.3 MPa

–

Carbon–Jute [50]

1.9 J impact resistant

S–Fibre Glass–Jute Higher on balanced [51] sequence Glass Fibre–Sisal [44]

44.917 kJ/m2 impact strength

380

213.02 MPa

–

1175

50.26 MPa

Yes

159

48 MPa

–

41.7% greater flexural strength. The results demonstrated that the hybridization technique used in hybrid reinforced composites affects the mechanical behaviour of laminates and the formation and spread of damage. Using techniques such as differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical testing, Chinnasamy et al. [54] examine the thermal properties and mechanical capabilities of glass and Kevlar fibre hybrid fabrics. According to Kumari and Kumar [55], a composite with a polymer matrix reinforced with carbon fibre and graphene at the micro and nano levels can be used as an alternative material for aluminium components of Orthotic callipers, thereby making the calliper lighter and more durable. The studies of previous synthetic material hybridizations are showed in Table 7.

5.4 Hybridisation with Natural Fibres Cotton, sisal, jute, wool, flax, and silk are among the world’s most popular natural fibres. Jute, a natural fibre, is one of the most significant in the world, with enormous supplies in China, Thailand, and other African countries, as well as on the Indian

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Table 7 Data analysis of previous studies Materials

Maximum Maximum tensile test data flexural test data

Thermal Fatigue Stab resistance properties test test data testing

HFCL and HSCL [53]

193.04 MPa (HSCL)

253.87 MPa (HFCL)

–

–

–

Kevlar–Fiberglass [54]

–

–

Yes

–

–

Carbon–Fiberglass [56]

–

714 MPa

–

Yes

–

Carbon–Aramid–Carbon – [57]

Approximately – 420 MPa

–

Approximately 0.6 mm

Glass–Carbon–Kevlar [58]

385.09 MPa

–

–

–

–

Graphene–Carbon [55]

Approximately Approximately – 1000 MPa 3000 MPa

–

–

Aluminium–Kevlar [59]

–

–

–

Yes

–

CFRP–Aluminium [60]

Approximately – 800 MPa

–

Yes

–

continent. For a variety of reasons, including cheaper end product costs, greater fibre processing performance, and ornamental aspects, the researchers attempted to blend jute with other natural fibres. This jute blending method consists of three steps: prior spinning, spinning, and post spinning. Cotton, kenaf, roselle, ramie, wool, pineapple leaf, and other natural fibres can be blended with jute [61]. Several previous studies on the hybridisation of natural fibres have primarily focused on mechanical properties, such as tensile, flexural, and impact strength, as well as physical properties, using tensile and flexural testing. Several studies, such as the hybrid of jute and ramie fibres [62] and the hybrid of banana, jute, and sisal fibre [63], concentrate on the mechanical properties of the hybrid, whereas others, such as the bamboo and jute fibre [64], concentrate on the tribological properties of the fibre rather than the mechanical properties. The evaluated enhancement parameter could be utilised in marine applications or to replace an automobile component [46, 47]. Table 8 summarises the test data for several studies related to this hybridisation type.

6 Conclusion Biodegradability and environmental friendliness are two benefits of using a hybridisation of natural fibre. It is simple to acquire natural fibre because it grows naturally through plantation. This could assist in reducing the amount of weight that a vehicle carries as well as the total cost of manufacturing a bumper. Natural fibre hybridization can also aid in the reduction of agricultural waste involving pineapple leaves.

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Table 8 Data on previous studies that been conducted Best material

Maximum tensile data

Maximum flexural data

Maximum compression data

Impact data

Jute–Ramie [62]

44.72 MPa

82.27 MPa

23.13 MPa

–

Sisal–Jute [63]

Approximately 34 MPa

Approximately 46 MPa

–

–

Three – layered–Jute [64]

–

–

–

Jute–Basalt [46]

–

162 MPa

–

4015.22 N peak force

Kenaf–Banana [47]

72.35 MPa

129.74 MPa

–

15.9 kJ/m2

Coil–Oil Palm EFB [65]

30.8 MPa

53 MPa

–

29.2 J/m

Kenaf–Bamboo [66]

–

99.4 MPa

–

44.8 J/m

Jute–Flax [67]

MPa

112.25 MPa

–

38.78 kJ/m2

Acknowledgements The research was supported by Universiti Tun Hussein Onn Malaysia (UTHM) through Tier 1 UTHM (Vot H773).

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Potential Application of Natural Fibre in the Aviation Industry Mohd Fadhli Zulkafli, Muhammad Naim Romzee, Ahmad Hamdan Ariffin, Fairuz Alias, Mohamad Norani Mansur, Mohammad Sukri Mustapa, and Abd Rahim Irfan

1 Aerospace Industry Aircraft manufacturing, airline industry, military aviation, and research companies are the crucial aspects in the aviation industry. The two main mechanical air transportations that are often used in the aviation industry are helicopters and aeroplanes. The aviation industry has also been the main contributor to the successful tourism industry. By boosting local economies through the tourism industry, the aviation industry has been a vital supporter of worldwide financial success because the industry has allowed for improvements to global trade [1]. Across the aviation industry value chain, millions of skilled and semi-skilled workers are employed directly and indirectly. The industry has been steadily growing in recent years, owing primarily to increased cargo and tourism worldwide [2]. The demand in aircraft manufacturing part will be increased due the increased in aircraft manufacturer demand. Therefore, the research on the aircraft part is also enhanced. In this chapter, aircraft radome is selected is one of the discussion topic.

M. F. Zulkafli (B) · M. N. Romzee · A. H. Ariffin · F. Alias · M. N. Mansur · M. S. Mustapa Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia e-mail: [email protected] M. F. Zulkafli · A. H. Ariffin Research Centre for Unmanned Vehicle (ReCUV), University Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia A. R. Irfan Faculty of Mechanical Engineering Technology, Universiti Malaysia Perlis, Kampus Tetap Pauh Putra, 02600 Arau, Perlis, Malaysia Green Design and Manufacture Research Group, Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Universiti Malaysia Perlis, 01000 Kangar, Perlis, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_9

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Fig. 1 Aircraft radome [4]

2 Aircraft Radome A weatherproof and electromagnetically transparent protective enclosure mounted on an aircraft is referred to as an aircraft radome. For such requesting applications, radomes serve an assortment of functions, such as outdoor protection from UV damage, temperature fluctuations, rain, wind, and snow, all of which can disturb an aircraft’s telemetry and radar systems. In order to keep the antenna can function effectively and adequately, the radome must be constructed or built with appropriate materials and designs [3]. Figure 1 shows the example of radome that can be found in every type of aircraft in the aviation industry.

3 The Material in Aircraft Radome Materials used in radome must possess a high ductility and dielectric characteristic. The most usual dielectric materials used for constructing an aircraft radome are polyurethane foam due to its low dielectric constants properties that are very useful in radio frequencies application [3]. Next, most prior research shows that the fabricated quartz fibre composite honeycomb is also one of the common material used in aerospace radome application. Previous research conducted by Liu et al. [5] shows high potential and possibility of the quartz fiber composite honeycomb to be applied in multifunctional radome application because it can maintain strong bending stiffness and mechanical properties at low-density condition. Composite materials such as glass fibre reinforced polymer, carbon fibre reinforced polymer, and phenolic resin impregnated aramid paper has been a common materials in aircraft’s wing and radome manufacturing. Usually, those composite materials will designed into a lightweight honeycomb structure because the structure will increasing the mechanical properties such as high energy absorption, strong specific stifness, and a high specific strength.

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4 Natural Fiber Reinforced Composite Natural fibers have been recognised as important material that possesses environmentally friendly properties such as biodegradable that can overcome current environmental and biological issues in engineering industries [6]. Natural fibers like kenaf, pineapple leaves, and bamboo fiber own a better properties and benefits from other synthetic fibers especially have non-corrosive nature, high strength-to-weight ratio, high fracture toughness, and sustainability. Polymer resin matrix that entrenched with natural cellulose fibers potentially to be the main materials that also can give many contributions in engineering especially in an industrial application which includes structural, construction, automotive, and aerospace [7]. Additionally, natural fibers is more promising from other synthetic fiber polymers because natural fiber composites possess advantages in mechanical properties such as low density, high specific strength properties, high toughness and amazing environmental benefits. Main example of environmental benefit for natural fibre is the material do not return the excess carbon dioxide to the atmosphere when go through composting and combustion process [8]. Previous article from Karimah et al. [9] emphasized the potentiality of natural fibre to be a favourable eco-friendly composite due to its unique properties such as lightweight, low-cost, and biodegradable. Besides, more experiment and research need to be done in order to utilise and enhance its mechanical properties and sustainability before applying it at engineering application such as polymer composite reinforcement. Next, Rajeshkumar et al. [10] conclude that strong interfacial bonding and physical entanglement between cellulose fibres in the matrix of the polylactid acid (PLA) will enhanced mechanical and properties of polylactic acid (PLA) reinforced with natural fibres. As result, the presence of cellulose fibre reinforcement can improve mechanical and tribological properties in composite that can contribute to structural applications.

4.1 Pineapple Leaves Fiber The pineapple (Ananas comoscus) commonly can be found at Africa, South Central America, and Asia is considered as one of tropical fruit that mostly cultivated after banana. Fibres that extracted from the pineapple leaves own a low microfibrillar angle and high cellulose percentage that enhance the mechanical properties of the fibre [11]. Previous studies have emphasized pineapple leaf fibre possess outstanding mechanical properties compared to other natural fibres due to lignocellulosic and multicellular characteristics [12]. A series of recent studies has indicated that pineapple leaf fibres are suitable and effective reinforcement for polyester matrix composites because it can improve the mechanical properties. Previous results show the improved strength of a polyester matrix composites and elastic modulus tend to increase if the volume of fraction of PALF also increased. The results successfully

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indicated that excellent flexural result from pineapple leaf fibre polyester matrix composites compared to other material with same the composites [13]. Article by Senthilkumar et al. [14] shows improvement in mechanical and dynamic characteristics of Biocomposites with 35wt% PALF fibre loading can be used in low strength application. Biocomposites with 35wt% possess high tensile and flexural strength that can be a worthy replacement for cementitious composite. For surface treatment, 30wt% pineapple fibre that undergo alkaline treatment possess a good enhancement in mechanical properties and thermal properties due to better-purified cellulose of the fibre [15].

4.2 Kenaf Fiber Ambary hemp or Kenaf (Hibiscus cannabinus L.) is one of the common plant that can be found at Africa, Malaysia, India, China, and Bangladesh. Natural fiber in the Kenaf plant is similar to jute fiber and commonly used as reinforcement in polymer matrix composite. A series of recent studies has indicated that Kenaf fiber is a suitable natural fiber that can use as reinforcement in polymer compoites due to its amazing mechanical properties and non abrasiveness during processing compared to synthetic fiber like glass fibers [12]. It was reported in literature that Kenaf fiber is the most ideal and encouraging natural fiber because of its benefits such as have possibility of harvesting twice a year due to its short growth cycle and its flexibility to ecological and environmental conditions [8]. Next, kenaf fibre can be a high quality and effective reinforcement that can improve mechanical properties such as flexural strength, tensile strength, and Young’s modulus of cement composite. Kenaf fibre reinforced composite also have a good ductility comparing to other synthetic composite when undergo compressive test due to slow crack expansion at the microstructure [16]. Futhermore, an experiment made by Rozyanty et al. [17] conclude that a interfacial adhesion between water retted bast in water retted kenaf bast fibres reinforced UPE composites will resulting a high tensile strength and resistance property to water absorption. Due to unique properties of water retted kenaf bast fibres reinforced UPE composite, it can contribute to civil construction industry especially in structural applications such as window panel and floor decking. Moreover, good wear resistance of epoxy-kenaf long fibre reinforced polymer matrix composites can be used in tribological applications such as automotive body panels due to good tribological properties like low coefficient of friction [18].

4.3 Bamboo Fiber Bamboo (Bambusa vulgaris) is another common plant that we can found in forest of tropical zones and tropical zones. Previous record shows that bamboo fiber cells are composed of lignin, hemicellulose, and cellulose that enhance the strength of

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glucose chains that resulting a high tensile strength due to formation of microfibrils [19]. Due to its strong mechanical properties, lightweight and low-cost, some researchers and material scientist believed it can be a possible alternative to synthetic fiber and can give a positive impact to structural applications in civil and construction engineering industries [20]. Like pineapple leave, bamboo fibre also can be a good material for reinforcement in polymeric composites because the bamboo fibre reinforced composite will resulting a good mechanical and can be use widely in engineering applications and industries. A recent study by Lopes et al. [21] concluded that bamboo fibre reinforced composite and carbon steel have an approximate value of tensile strength. From the statement itself, it shows that bamboo fibre can be a high potential natural fibre that will be demand by engineering industries because it can maintain and improve the properties of polymeric composites. Futhermore, Manoj Prabhakar et al. [22] conclude that bamboo fiber have a high potentiality to be a good reinforcement for nano composite that can be use in automotive industry especially in automobile outer bodies manufacturing due to their strong flexural strength. For 12.65 kgf, bamboo composite can withstand the load and resulting a 60.25 MPa for its flexural strength. Thus, it shows that bamboo composites also have a potential to replace other synthetic materials in automotive manufacturing. Moreover, a research made by Tang et al. [23] shows the effect of bamboo fibre as reinforcement that enhanced the mechanical strength of phenolic foam composites. Strong mechanical properties of bamboo fibre such as flexural strength and thermal stability clearly shows that addition of natural fibre into resin matrix can give many advantages to engineering application.

5 Material Analysis and Testing A further question is whether the material is suitable to become possible main materials for some applications and components. Some common materials that used in engineering industries such as plastics, composites, polymer, and ceramics are compulsory to go through environmental, durability, and performance testing in order to analyse either these material’s properties can withstand some extreme conditions or not. Destructive test such tensile and impact test will shows the material’s failure and the results are very important to predict the material’s lifetime and durability before applying it into engineering applications [24]. A numbers of authors have recognized polymerics material failure and deteriorations can make the material’s properties and performance drop due environmental factors. Zhang et al. [25] conclude that mechanical and moisture behaviour of epoxy adhesives can be affected by environmental conditions. The author also highlighted that major mechanical properties such as tensile strength and shear properties tend to decrease and when exposed in high moisture and temperature condition. Moreover, Preetham et al. [26] stated that environmental factor such as acid rains can results a structure failure due to material degradation. Degradation of cement composites will occur due to reduction process

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that resulting a formation sulphuric acid due to sewage and chemical wastes exposure. Environmental aging factors such as ultraviolet light will affect the polymeric material’s molecular structure and aggregation of the structure. To analyse the degradation, specific material testing needs to be done by the engineers in order to evaluate and predict the strength of those materials for engineering applications and meet the requirements needed from industries [27].

5.1 Tensile Test The tensile test can be classified as the most important and common mechanical test because it can show the mechanical property for material such as tensile strength and ductility. Tensile strength is one of the major mechanical property that engineers need to measure before applying the material into engineering. In other words, tensile strength can be a specific indicator to know how the material can withstand when two forces try to separate it in different directions [28]. To analyze and determine the mechanical strength properties of resin materials, usually it will follow ISO 527, ASTM D638, and JIS K 7169 because it is a usual standards for universal testing machine’s specimen requirement [29]. The ISO 527 standard are suitable for rigid and semi-rigid moulding, rigid and semi-rigid thermosetting moulding materials, fibre-reinforced thermosets and thermoplastic composites, and thermotropic liquid crystal polymers [30]. For tensile testing, this research will follow the ISO 527 which is an international standard to obtain the young modulus and tensile strength data for reinforced plastics [31]. In terms of procedure, elongation and tensile strength data will be measured by extensometer. Next, 5 or 50 mm/min value will be the standard test speed for analyze 1 mm/min for measuring the modulus data for ISO 527 [32].

6 Conclusion In aerospace industry, most early studies as well as current work focus on enhancing the quality and safety aspect especially in the aircraft’s component. From the previous study, it shows that only several polymer composites that approved to be main materials in aircraft’s parts manufacturing due to its strong properties. Besides that, natural fibre also shows almost an equivalent quality to the existing polymer composite and synthetic fibre. Therefore, the usage of natural fibre is feasible and can reduce the dependence of synthetic fibre. However, due to the strict procedure and regulation in aviation industry, the analysis on natural fibre need to be explored rigorously. Acknowledgements The research was supported by Universiti Tun Hussein Onn Malaysia (UTHM) through Tier 1 UTHM (Vot H773) and Geran Kontrak UTHM (H870)

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Natural Fibre for Composite Structural Application Siti Amira Othman, Nur Nadia Nasir, and Nor Farah Amirah Nor Azman

1 Introduction Recently, natural fibre composite has been enormously employed by researchers to improve the composite structure of the material. Composite defines as a combination of two materials with different characteristics. As a result, this combination helps in the improvement of the characteristics themselves. In terms of natural fibers, indirectly the composite properties will help in yielding the strong, durable and increase other properties of the material as well. This paper will discuss the comprehensive application of natural fibre in the production of bioplastics and papers. Since the 1950s, approximately 1 billion tons of plastic have been a dump and some of the plastic might exist for centuries or even longer [1]. The advantage and also their disadvantage of plastic is its durability. Increasing utilization of plastic has turned into an issue in numerous perspectives. By 2020, expecting to increase in the production of bioplastic or biodegradable plastic [2]. Therefore, the rising favor in bioplastic is observed. Bioplastic means biodegradable plastic or biomass-based or both [3]. Commercial biodegradable plastic can be divided into; (a) polylactide-based plastic (PLA), (b) starch-based plastic, (c) cellulose-based plastic, (d) lignin-based plastic, (e) polyhydroxyalkanoate-based plastic and (f) aliphatic–aromatic polyester-based plastic. PLA is now being utilised in packaging applications.

S. A. Othman (B) · N. N. Nasir · N. F. A. N. Azman Department of Physics and Chemistry, Faculty of Applied Sciences and Technology, Universiti Tun Hussein Onn Malaysia, 84600 Pagoh, Johor, Malaysia e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_10

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Changing from PLA to starch-based is because of starch-based containing polyesters that will improve processability, water-resistance and tear strength [4]. Also, most of the starch is polysaccharides and 75% of all organic material on earth is present in the form of polysaccharides. Starch-based plastic is usually from rice, wheat, corn and potatoes. Corn starch is the most affordable and widely used starch-based plastic. However, starch-based bioplastic faces several problems such as poor mechanical properties and lack of water barrier [5]. Various research has been conducted to improve starch-based bioplastic properties. The growing research interest, the effect of ionizing radiation on polymer because of changes in physical and chemical properties were impacted by degradation reaction or induction of crosslinking, change in degree of crystallinity, isomerization and more [6]. About 24% of plastic waste is labeled as the second major contributor to the average composition of solid waste in Malaysia [7]. There is a growing debate about the environmental concern with plastic is becoming a more serious topic. Technically all conventional plastics are degradable but because of slow breakdown, it’s considered non-degradable. The major contributor to plastic waste is polyethylene. One extensive practice to reduce plastic waste in the environment is recycling plastic. However, a lot of problems occur using this process and sometimes this process is more expensive than producing new plastic. Therefore, the rising favor in bioplastic is observed. There are several types of bioplastic such as PLA, starch-based plastic and more. In recent years, starch-based plastic has drawn the interest of the researcher. Several of the factors that affect the development of starch-based plastic are better product quality, abundant, inexpensive and renewable resources [8]. The most commonly used starch for starch-based bioplastic is corn starch. However, starch-based plastic is brittle and hydrophilic therefore it limits its processing and application and led to a problem such as a lack of water barrier, poor mechanical properties and more. Besides plastic, any sort of fibre may be used to make paper, from wood or non-wood fiber and from your old cloth to grass clippings [9]. Paper can be made from fibers of cellulose or recycled paper and the chemical substances depend on the material that is used. In the year 2009, global paper and paperboard production reached 367.8 million. Natural fiber such as banana fiber content has many advantages such as low density, high stiffness and high disposability and renewability [10]. For making paper, only some of the banana species which have high cellulose content of pseudostem is used in the papermaking and pulping industry since the 60s. Banana or in the scientific name call Musa Paradisiaca, Musa Sapientum, Musa Cavendishii and Musa Chinensisare all the types of banana species that can make paper from the banana fiber as the fiber has various strength, color and discrete length As the banana tree is non-wood fiber and it is an alternative way to find the new renewable raw material to make paper without harming the environment, banana is a good choice, in the meantime, it also helps in increase the national economic growth [11].

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Recycling or recovery materials can be done by process segregation, collection and reprocessing, for the products which can give value, it is good for the waste challenge management and this can give huge economic opportunities [12]. As nonwood fiber is much cheaper than wood fiber, recycled paper is also low in price than wood pulp. Recycled paper is also technically eco-friendly and secured to use [13]. Fungi can decrease the function of the cellulose fiber and can cause spots or stains on paper and this will affect the integrity of the paper. The fungi usually can be obtained during the process of making the paper or the chemical being used to make the paper [14].

2 Corn-Starch Based Bioplastics Nowadays, bioplastic is another alternative for almost all conventional plastic materials and applications. Based on the raw material use, bioplastics will have the same properties as conventional plastics. Based on Andrej, bioplastic is plastics that are biodegradable or biomass-based or both. Bioplastics are a new generation of plastics and generally are derived from renewable raw materials such as starch which are not hazardous and will decompose into carbon dioxide [15]. Currently, bioplastics are used in an application such as packaging, catering products, consumer electronics, automotive, agriculture/horticulture and toys to textiles and others [16]. Packaging application remains the largest usage of bioplastics for almost 60% (1.2 million tonnes) with the total bioplastics market in 2017. Bioplastic can be divided into four parts which are directly extracted from biomass, synthesized from a bio-derived monomer, the biodegradable polymer synthesized from petrochemicals and produced directly by natural/genetically modified organisms. Starch-based bioplastic was directly extracted from biomass. However, the most commercially available is polylactic acid (PLA). PLA is commonly made from starch or sugar-rich crop but it’s also from the derivation of petrochemicals. PLA has similar properties to polyethylene terephthalate (PET) but for elasticity, it acts a lot like Polypropylene (PP) [11]. PLA also has excellent organoleptic characteristics which are compatible with packaging applications [17]. PLA also has the largest range of applications because of its ability to be stress and thermally crystallized in most polymer processing. Due to PLA’s relatively slow biodegradability and it’s quite expensive, there is numerous study on the usage of starch as raw material for plastic with a short-lived application such as packaging [18]. Starch-based bioplastic is usually from rice, wheat, corn and potatoes. Corn starch is the cheapest, most commonly used for starch-based plastic and has also been used as a source for sustainable and eco-friendly raw material. The development of starchbased bioplastic was influenced by the factor which is to produce better product quality, abundant, cheap and a renewable resource [9]. Starch-based bioplastic also contains additives such as plasticizers and compatibilizers to improve processability,

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water-resistance and tear strength. Starch contains two main anhydroglucose polymers which are amylose and amylopectin. The ratio of amylose and amylopectin for corn is 28% and 72% respectively. Starch-based bioplastic offers so many advantages such as healthy cancer-free, pollution-free, do not cause the death of marine animals, requiring less energy to be produced, light weighed which can be used for the production of plastic carry bags, reduce the dependency on fossil fuels for the production, made from renewable raw material and more [19]. However, they are brittle and hydrophilic therefore it limiting their processing and application which led to a problem such as lack of water barrier, poor mechanical properties and more. There is numerous research that had been carried out to improve starch-based bioplastic some of it is a plasticizer, blend with other natural polymer or artificial polymer and ionizing radiation [16]. In general, plasticizers were added is to reduce brittleness, impart flexibility and reduce recrystallize of starch [20]. The main role of a plasticizer is to reduce the strong intermolecular interaction between starch molecules by enhancing the flexibility and processibility of starch [21, 22]. By using a plasticizer, the brittle problem of starch can be decreased. However, for excellent plasticization, the compatibility and miscibility between polymer and plasticizer are very important [23]. Also, molecular weight and the concentration of plasticizers should be considered for effective plasticization. Each polymer required a different plasticizer. The commonly used plasticizer are glycerol, glycol, water, sorbitol and more [24]. The most common plasticizer used in processing starch-based bioplastic is water and glycerol. However, for gelatinization of cornstarch various glycols (polyethylene glycol (PEG), glycol, tri- ethylene glycol) and glycerol have been used as plasticizers [25]. Several studies have shown that glycerol is the best water-soluble polymer and also to change the physical properties and also it has the highest water absorption among the others due to the presence of 3 hydroxyl.

2.1 Irradiation Towards Bioplastic Exposure to ionizing radiation may lead to the formation of free radical, ions, excited state and many very reactive intermediates, and it will involve many chemical reactions even after the irradiation process which is lead to intensive research on the effect of radiation on starch-based bioplastic [11]. According to Salwa to modify the polymeric materials, the ionizing radiation is established well for material processing. Ionizing radiation can be divided into types of radiations such as x-ray, gamma-ray, electromagnetic waves, beta ray, electron beam, heavy particle and neutron beams. Commonly used radiation in industrial were electron beam and gamma radiation [7]. Ionizing radiation can lead to modification of polymer properties through cross-linking and it also led to the formation of free radical ions, excited states and many very reactive intermediates [9].

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Krystyna et al. state that irradiation using gamma source led to the improvement of hydrophobic properties of the potato and wheat starch-based films. Also, there is an improvement in the strength and flexibility of the potato starch-based film [26]. By using scanning electron microscopy (SEM), it has been found that irradiation improves the structural properties of the potato starch-based film. Krystyna et al. conclude that radiation treatment appears a proper method to improve the starchbased film properties and it is also possible for edible packaging. Based on Ali [8], radiation processing proves to be a good alternative to chemical modification. Starch-based bioplastic is appropriate for packaging material when it was irradiated by 5 kGy dosage which led to the improvement of mechanical and thermal properties. However, when the irradiation dose was higher than 20 kGy there is decreasing in tensile strength. Another study has been done by Antonio et.al on the effect of ionizing radiation on starch-based plastic for food packaging application, is shown that using irradiation dose below 25 kGy will not compromise the structure of the polymer. Shafik et al. research on the effect of gamma radiation on starchbased blend with PVA film led to improvement in tensile strength and elongation to break due to cross-linking caused by a chemical reaction under influence of ionizing radiation [5]. The sample was irradiated up to 95 kGy, as the dosage increases, the tensile strength increases however if the dose continues to increase (≥ 60 kGy), the tensile strength will decrease due to degradation at a higher dosage. According to Natalia et.al, irradiation of cassava starch-based using gamma radiation produce a stable formulation and led to the improvement of mechanical and barrier properties [27, 28]. As the dosage increase, the water absorption will increase however it is still acceptable compare to non-irradiated cassava starch-based. In conclusion, based on previous studies have shown that usage of ionizing radiation will improve the properties of starch-based bioplastic.

3 Banana Paper According to Jawaid [29], the reason which leads to the invention and development of natural materials with a focus on renewable raw materials are increased pressure from environmental activists, preservation of natural resources and attended stringency of laws passed by developing countries. The natural fiber is more preferred than synthetic fiber because natural fiber is biodegradable, cheap, lightweight and abundant. The strength and stiffness of natural fiber is higher than synthetic fiber because of the hydrogen bond and other linkages provided to the cellulosic fiber [30]. Saheb [30], also classified that natural fibers have three types of a group is seed hairs, bast fibers and leaf fibers depending on their source. For example, cotton for seed hairs, ramie, jute and flax for bast fibers and sisal and banana for leaf fibers. The banana pseudostem and fruit-stem bunch can be found in tropical and subtropical countries on a very large scale and this can show a major income source in countries and communities.

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In the banana field, the banana plant can only be harvested once and this makes the pseudostem and the unused part will be fell and this will make the stem attack by the fungi [31]. Usually, the residue of the banana plant will become organic matter after being left on the field. A plant that is left behind without any removal usually becomes a place for a disease vector for example place for mosquitoes and fruit flies, it will also enhance pests’ proliferation for rats and snails and lastly, it will bring a bad aesthetic [32]. The pseudostem is the main part of the banana plant as it serves three main functions in a tree which are to hold the glass, transport water and mineral and act as food storage [33]. The pseudostem contains cellulosic fibers that can be exploited in a paper mill. The study of the fiber was made to make the fiber can work in pulp and subsequent evaluation of its suitability and paper. The chemical and mechanical process is used to make the study success and this proves that the banana fiber can be used in the pulp and paper industry for paper making. This makes the banana fiber an annual fiber, similar to sugar cane bagasse. There are many reasons that banana fiber is a good choice in new raw materials for making paper. As the banana pseudostem is fast growing and has a yield high of biomass, we can use it as a new raw material for making paper [34]. For mechanical properties in bast fibre, high content of cellulose and low microfibril angle impart are important. In the lignocellulosic material, lignin and hemicellulose play an important role in the natural decay resistance. This can be seen through the composition of banana pseudostem in element analysis. The banana plant can exist in varieties which is different in color, size and taste of banana fruit produced [35]. The banana plant contributes various polymers such as cellulose, hemicellulose, pectin and lignin. The polymers are the ones that provide fiber with strong mechanical properties. As fiber is important for papermaking, the fiber needs to be firm. Based on Abdul Khalil [36], evaluate that the cell wall structure, the chemical composition, anatomy and lignin distribution of banana stem fiber. The fiber of banana pseudostem has a high Young’s Modulus and higher water absorption capacity. The banana pseudostem is a new raw material for a paper due to its high tensile strength and stiffness. The banana fiber consists of rich fiber cellulose, its cellulose fraction is not easily accessible to the enzyme digestion because of the lignocellulosic nature of banana pseudostem and this makes the banana paper is high in resistance to indigestion than the paper from the wood [37]. The utilization of banana fiber is better for pulp, textile and paper making because the higher pentosan content together with gums and mucilage in the sheath of certain species of the banana plant and make it a suitable source for producing greaseproof paper. Ekhuemelo [38] classified that it is important to separate the lignin from its cellulose in the paper industry. For sources like wood, it will be difficult to separate and highly toxic chemical substances are needed, but for the banana finer as the lignin is low in content, easy to remove and separate the lignin, no chemical substances are used and this makes the banana paper environmental friendly.

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3.1 Recycled Paper Based on [39], one of the best recycling waste schemes applied to waste materials today is paper recycling other than glass and plastic. In paper and pulp industry production, recycled paper is essential in Europe as the estimated utilization is about 72% in 2012 which increase 20% from the years 2000. In the paper industry, recycled paper is becoming an important raw material other than fiber from wood [40]. In various studies, it also has been demonstrated that paper recycling has offered significant benefits from a lifecycle perspective especially in the environment. Recycling is understood as material domestic flow in the Eurostat material balance scheme, but recycling is treated as more than just a regional material flow in the pulp and paper industry. Millions of tons of recycled paper are imported from Europe to China because according to the European Recovered Paper Council, the export of recycled paper is also known as European Recycling [41]. Paper and board production today use more recycled paper than virgin fiber as input. In between 1970 and 1980, the recycled paper collection has increased to 64.3%, then 66.7% between 1980 and 1990. In the years between 1990 and 2000, the recycled paper collection increased to 69.7%, and by 45.4% between 2000 and 2010. The development of recycled paper has been continued for years to years as the technology has been improved for better production [42]. From the year 1990 to 2007, the production of paper recycling and the paper board has increased gradually, but the global crisis drops down the all economic sectors including the pulp and paper industry. However, the production of paper seems quite stable since the year 2010, but the production of paper and board is decreasing in amount rather than before the global crisis. The production of paper and board has increased around 1.4% every year since 1990. In the year 2015, the production of packaging paper represented around 50% as this is the same as the consumption of paper every year. As the forested lands and the croplands have limited capacity to supply enough cellulosic materials so that the production of recycling paper is increasing day by day [43]. The production of paper is highly in demand in various mechanical characteristics and this makes the paper producers use high-quality fibers and/or treat the pulp by using mechanical refining especially when using recycling paper fiber as the new raw materials. If resources saving strategies is used in making the paper, for example, decreasing basis weight or increasing mineral filler content in the paper product, the challenging part of the requirements for various mechanical is the strength of the paper, as the strength of the paper will decrease [44]. Delgado-Aguilar [45] also classified that in the paper-making application, the use of cellulose fibers is probably the most explored. The cellulose-based fibers can be as coating agents or as modified for specific purposes, the cellulose can be added at the bulk of the pulp or paper slurry. As society keeps on pressuring about the friendly environment, recycling is one of the processes to help and maintain the environment’s cleanness. Many advantages can be obtained, if the recycling process can be done, for example, the natural resources

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are saved, emissions are decreased and the burden of the solid waste can be reduced. The recycling process can create employments and attracts investments and this can increase economic growth [46]. In the North and South, there is difference and various for the development of recycling. In the North region, the reasons which recycling become increase because of the higher disposal costs, increased public concern about the health and environmental impacts of waste disposal and the perception that recycling promotes resource conservation and because of that, recycling paper is important in each country [47]. In the south region, the recycling process is because of economic motives. Based on [47] the prices for recycled paper are cheaper than the wood pulp even sometimes the prices of the market are high. The availability of recycled paper is secured and its usage is economically rational when it is used as a new raw material for the pulp and paper industry. The increase in the high demand for recycled paper is due to the environmental regulation and the consciousness of the producers and the consumers level in acknowledgment [13, 48]. Environmental issues have been surging for decades and awareness has been promoted by education. There are two ratios for the country’s status which respect to recycled paper. One is the recovery rate and the other one is the utilization rate. The difference between the recovery rate and the utilization rate is their function. The recovery rate (RR) measures the supply of recovered paper from domestic sources while the utilization rate (UR), denotes the extent to which recycled paper is used in paper and board production [49]. Furthermore, the recyclability of the waste paper becomes significant in life due to the increase of the volume of digitally printed products and this makes the materials that can be reused are accepting the cradle-to-cradle concept. As the world becomes more globalized, it increased many factors to the production of paper and in the paper and pulp industry especially in the relationship between the production and product, the materials that are used and the generation of waste are becoming more complex and geographically dispersed [50].

3.2 Radiation on Paper As to maintain the environmentally friendly and to reduce the cost of pulp and paper production, it is important to find another alternative technique to recover or improve the virgin paper or recycled paper, to make the life span of the paper increasing and at the same time, the paper can stand with strength and also are not harmful to use especially free from fungi and bacteria. The presence of potentially harmful chemical substances in the paper has been an increase from day by day and researchers have already voiced it out within recent years [51]. The harm of the paper can be seen when the migration of chemicals from packaging materials into food [52].

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There are many types of radiation sources and one of the radiation sources is gamma radiation. Gamma radiation characteristic has high energy, forming from the ionizing electromagnetic radiation and gamma radiation can penetrate through the wooden objects or the products from the wood such as paper. It is very effective in the context of disinfection of wooden products such as paper and board [53]. There is a difference between the alpha and the beta rays with the gamma radiation, for the alpha and beta rays, only penetrate a very thin layer, however, the gamma radiation can fully penetrate wooden objects or wooden products [54]. The gamma-ray which is rich in energy can change and modify the cellular structure of the paper and this can bring to the unexpected function of the living cells or their death. When the high dose is being used on the fungi, the elimination of fungi and insects can be done, as the insect cannot withstand the doses from 0.7 and 1.3 kGy [55]. As a sterilizing treatment, gamma radiation can cause direct damage to the cellular DNA and also cause the single and double-strand of the cellular DNA to break, because of the radiolysis of the cellular water and the formation of active free radical. Gamma-ray is used because can pass through the cellular without leaving any waste behind. This technology has been used for over 50 years in the food and packaging industry but still not in the pulp and paper industry because of the lack of knowledge and realization of the producers and consumers. However, this method can make the paper acidification, the color of the paper consequently yellow and the mechanical strength of the cellular is reduced due to the structural damage [56]. The time taken for the radiation is based on the power of the radiation source and there was no difference if the weaker source but used for a long time or the strong sources but used in a short time. The significance of the radiation to detect the difference is when the difference quantity dose of absorbed dose is used, where the absorbed dose is known as the amount of absorbed energy per mass unit [57]. In the radiation of paper, measuring the quantity of the absorbed energy by the paper sample is more important instead of measuring the applied energy. This is due to the number of an electron within a beam which will interact or react with the paper as a function of the energy of the electron. The safety condition must be taken when the radiation process is working on, it is recommended to use the lowest radiation dose possible for the radiation process to be successfully applied especially to the books decontamination [58]. To determine the effectiveness of the bleaching cellulose pulp or measuring the aging of the paper after the radiation, color brightness can be done since it can detect the change in the paper color on aging or degradation, as the blue and violet regions are the greatest in the spectrum. Based on [59] there are no specific regulations checks for the paper packaging food nowadays, but the items like plastics, bottles and glass brought into contact with the food and this way could be done to prevent the chemical substances from migrating into the food and gives side effect to the human.

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3.3 Properties and Structure of Paper In the manufacture of paper and paperboard, one of the most major components of abundant raw material which is predominantly used is pulp, other than paper and paperboard, the pulp is also important in textile industries, food or packaging material and also in pharmaceutical products which all the items related to cellulose where the cellulose and the fibers of the paper are important for the structure and properties of items. The raw material such as bananas and the manufacturing method are important to determine the mechanical properties and the cellulose structures of the papers. The durability and resistance towards environmental stress of the paper are largely independent of the mechanical properties of paper. The tensile strength of the paper is related to the ability of the paper to endure the tension condition, and the tensile strength of the paper between radiated and irradiated is also different. Based on [60] paper that is made from handmade, has a higher extent of crosslinking and cellulose polymerization. Few things need to be taken when using recycled paper as pulp. The fiber experiences structural damages because of the process of mechanical refining and hornification phenomena. This process is usually last used in newsprint production because the effect is higher in the kraft and sulfite than the high yields pulp [61]. Even though mechanical refining makes damage to fiber structure, mechanical refining increase the specific surfaces of the fibers promotes swelling capacity and also increases the mechanical properties of the paper. However, in long-term conditions, the structural damage and fines creation will have a direct impact on the life span of paper and pulp drain ability. The paper that is made from recycled paper from the industries such as A4 paper or newspaper has been superficially treated with starch and usually, this treatment can increase the tensile strength of paper by about 12%. This makes the tensile strength of the paper between the recycled paper and the paper from raw material such as banana paper is different. The tensile resistance of the recycled paper increased as the paper stiffness increased as well. The increase of the mechanical properties of the recycled paper usually comes from the increase in the surface of fibers and the capacity of fiber swelling, due to that the inter-fiber bond increase. The depolymerize cellulose of paper fiber can lose the fiber strength of the paper and this can affect the structure and the properties of paper. For absorbing and breaking the bonds in the cellulose without the need for oxygen, X-ray and highenergy electrons are ready and can be used. The photolytic scission is direct to the cellulose chain, the pulp or the fibers of paper will become irradiation swells, increase hygroscopicity and this will make the cellulose more soluble in alkaline solution and more susceptible to acid hydrolysis for examples sodium hydroxide. Based on [62], to achieve the objective for improving the paper fiber digestibility and reactivity toward hydrolysis or chemical substances, the electron beam has been used, it has been shown that depolymerization of the cellulose can make the fibers lose their strength in structure and properties. The decrease in depolymerization of

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the cellulose is because of the irradiation strength, and this will make the pulp and paper are hard to make and bond together and the surface of the paper is rough. The paper integrity can be affected by the fungi which can degrade its cellulose fiber, when the cellulose fiber is affected, the structure and properties of the paper are changed. Many types of fungi can be found on the paper but one of the types is Cladosporium, and this fungus is prevalent in the paper especially in Brazil and many other countries compared between the paper damage for accelerated aging and gamma radiation, the resulted state that the structure of paper that is being radiation is much better than the paper that is irradiate [63]. In India, the fibers of the banana plant are not only used for paper but also can be used for handicrafts, ropes and textiles. The agro-based fiber cannot still produce a product by using bio fiber, as the fiber is high in moisture absorption of the natural fibers, making it difficult for the hydrophobic fibers and hydrophilic polymers to bond together and for the paper, this will make the structure and the surface of the paper is not smooth like the paper from the wood mill [64].

4 Conclusion A natural fiber that was applied in the plastics and paper was exaggerated with irradiation method help in enhanced the composite structure of the materials. These will be promising materials in the future. Acknowledgements The authors would like to thank the Faculty of Applied Sciences and Technology for the facilities provided that make the research possible.

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Overview of Unmanned Aerial Vehicle (UAV) Parts Material in Recent Application Mohd. Rasidi Ibrahim, Muhamad Firdaus Azman, Ahmad Hamdan Ariffin, Mohamad Norani Mansur, Mohammad Sukri Mustapa, and Abdul Rahim Irfan

1 Introduction Rotorcraft was a first build by Paul Cornu, a French inventor and at the same time the Wright brothers were taking flight. On November 13, 1907, his “Cornu” helicopter, which was built up of nothing more than tubing, an engine, and rotary wings, achieved a lift height of about one foot while being in the air for about 20s [1]. Nowadays, aviation industry growth faster than the expectation. Unmanned Aerial Vehicles (UAV) has been introduced. Drones, which were originally designed for military use, have seen fast growth and advancements and have made their way into consumer gadgets. Initially, drones were used as weapons, in the form of remotelyguided aerial missile launchers. Drones, on the other hand, have a wide range of civilian applications nowadays, particularly in the form of small quadcopters and

Mohd. R. Ibrahim (B) · M. F. Azman · A. H. Ariffin Research Centre for Unmanned Vehicle (ReCUV), Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia e-mail: [email protected] A. H. Ariffin e-mail: [email protected] Mohd. R. Ibrahim · M. F. Azman · A. H. Ariffin · M. N. Mansur · M. S. Mustapa Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia A. R. Irfan Faculty of Mechanical Engineering Technology, Universiti Malaysia Perlis, Kampus Tetap Pauh Putra, 02600 Arau, Perlis, Malaysia A. H. Ariffin · A. R. Irfan Green Design and Manufacture Research Group, Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Universiti Malaysia Perlis, 01000 Kangar, Perlis, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_11

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octocopters. Drones are being utilised for various purposes, including climate monitoring, transporting goods, assisting in search and rescue efforts, photography, and in the agriculture sector. Drones are increasingly being used in agriculture, and it also bring along a new potential and concerns. Drones are most frequently employed in agriculture to evaluate and monitor crops via remote sensing, but contemporary agriculture uses also include precise pesticide delivery, biological control agents, monitoring livestock health and remote sampling. Several distinct drone designs and sensor types are employed, each with its own set of benefits and drawbacks. The employment of wide-angle sensors at low elevations above ground level offers obstacles that required specific data collecting and processing approaches to overcome.

2 Unmanned Aerial Vehicle (UAV) Drones have made inroads into agriculture, technology, the military and police services, security and control, aerial surveillance, signalling, aerial filming, cartography, timely danger and fire signalling, surveillance missions, security, defence and attack. The following are the key advantages of drones over traditional aircraft; Significantly reduced fuel consumption and environmental polarisation, much lower design, production, maintenance and operation costs. Drones do not require pilots, are generally small and have lower manufacturing costs and materials. Moreover, it also very resistant to collisions, accidents with the drones being rare and without tragic consequences. It can operate a variety of things without a pilot, at lower costs and with better results than traditional aviation. The very customizable of materials used in industries is a simple approach to reduce the consumption of raw materials needed by businesses. It is a start must be made even with heavy industries and automobile manufacturers, especially those in aviation and aerospace. Compared to supplies held in ancient, traditional, massive ships, the use of materials by drones is astounding. Drones will be able to successfully intervene in place of large and heavy ships for other daily air operations. In facts, large public aircraft will still be required for public passenger transport which no matter how redesigned will consume a lot of materials and energy. In other side of daily air operations, drones will be able to successfully intervene in place of large and heavy ships. These areas will see massive material savings, not to mention the very low costs of people who will be replaced by robots, vending machines, cameras, low fuel consumption and the reduction. If not elimination, it can cause a massive pollution by the widespread use of large planes for any minor operations requiring flights. Drones have proven to be effective and efficient in completing big and essential areas of flight as well as tough and careful operations, with the drones having obviously expanded capabilities and penetration.

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Three Rotors

Two Rotors

Fig. 1 Multi-rotor drone types

3 Drone Innovation Perspective 3.1 Multi-rotor Drone Multi-rotors drones are the UAV that have more than two rotors with fixed-pitch spinning blades that generate lift. The drone can be made to ascend, hover, or descend by changing the speed of the rotors so that the thrust generated is greater than, equal to, or less than the forces of gravity and drag acting on the aircraft. It is also possible to fly the drone turn or move horizontally by varying the speeds of specific rotors. Multi-rotor drones can be classified based on the number of rotors on the platform. The drone can be classified as Tricopter (three rotors), Quadcopter (four rotors), Hexacopter (six rotors) and Octocopter (eight rotors). The quadcopters are the most widely used variant. The drones have excellent control over position and framing, making it ideal for aerial photography work. Hence the drone carrying a lightweight camera payload, the drone use is limited to around 20–30 min with current battery technology. Figure 1 shows the varieties of multi-rotor drones [2].

3.2 Fixed-Wing Drone Instead of vertical lift rotors, fixed-wing drones use a wing identical a normal aero plane to provide lift. As a result, it only needs to use energy to move forward rather than to hold itself up in the air, constructing it much more efficient. From that, the drone be able to cover longer distances, mapping greatly larger areas, and loiter

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Fig. 2 Fixed-wing drone

Fixed-wing

for extended periods of time monitoring the point of interest. In addition to greater efficiency, gas engines capable to used as their power source, and since of the higher energy density of fuel, many fixed-wing UAVs can stay aloft for 16 h or more. The main disadvantage of a fixed-wing aircraft is their inability to hover in one place, which eliminates fixed-wing drone from general aerial photography work. Figure 2 shows the example of a fixed-wing drone.

3.3 Single-Rotor Drone Single-rotor drones have a design and structure very similar to a helicopter. A single rotor model, as opposed to a multi rotor model, has only one large rotor and one small rotor on the tail of the drone to control its heading. A single- rotor helicopter has the advantage of being much more efficient than a multi-rotor, as well as being able to be powered by a gas motor for even greater endurance. In aerodynamics, the lower the number of rotors, the lower the spin of the object. From that theory, single rotor drones are much more efficient than multi-rotor drones. The disadvantages include their complexity, cost, vibration, and the danger posed by large spinning blades. Figure 3 shows the example of single-rotor drone. Fig. 3 Single-rotor drone

Single Rotor

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Fig. 4 Fixed-wing VTOL drone

3.4 Fixed-Wing Hybrid Vertical Take-Off Landing (VTOL) Drone These are hybrid models that combine the advantages of fixed-wing models (longer flight time) with those of rotor-based models (hover). This concept has been tested since the 1960s with little success. However, with the introduction of new generation sensors (gyros and accelerometers), this concept has taken on new life and direction. Hybrid VTOLs are a combination of automation and manual gliding. A vertical lift is used to lift the drone from the ground into the air. Gyros and accelerometers work in autopilot mode to keep the drone stable in the air. To guide the drone on the desired path, remote-based (or even programmed) manual control is used. Figure 4 shows the example of fixed-wing VTOL drone [3].

4 Drone Compartment Drones are complex gadgets made up of many different parts that function together. Because each component performs a particular purpose, different factors must be considered while selecting materials for each section. However, in order to minimise weight and maximise performance, the material density of each piece of a drone must be considered. Figure 5 shows the parts of the drone.

4.1 Drone Arm Drone arms are one of the important components in drone parts. The high durability of drone arm, the more efficient of drone performance can be produced. The main function of the drone arm is to be a connector the base frame drone with the propeller. The quantity of arms will depend on the quantity use of propellers.

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Fig. 5 Drone parts

There are multiple types of drone arm used such as unibody and replaceable arm. Mostly racing drone will used unibody arm since racing drone need to have a lighter drone which around 400–800 g with a battery. The racing drone arm will fix attached with the drone frame with one suitable material which is carbon fiber. Agriculture drone mostly will use replaceable arm and stitch arm because the main focused to build the agriculture drone is to lift up a heavy weight load such as pesticides and fertilisers. Furthermore, replaceable arm also can reduce spaced to stored and carrying everywhere to used it. The majority of agriculture was enormous, but with this replaceable arm, it can be transported more easily and reducing size. It can be tough to choose between a unibody and a replaceable arm frame. The convenience of usage of a unibody frame is due to the lack of the requirement to build a collection of carbon plates. Separate arm designs are frequently used due to their lower cost and ease of maintenance. Separate arm designs are often less expensive than unibody frames since it is squander less of the carbon sheet it will cut from. Because of the arms are removable, the quad can be built to be less weight due to the reduced width of the arms. In a situation which the arm breaks, it may be swiftly and inexpensively replaced. Separate arm frames replaceable nature improves dependability, which is a crucial feature to consider, especially when the chosen frame will be raced competitively.

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4.2 Drone Propeller Propellers are mechanical devices that convert rotational motion into linear thrust. Drone propellers produce lift for the aircraft by spinning and creating airflow, resulting in a pressure difference between the propeller’s top and bottom surfaces. This causes a mass of air to accelerate in one direction, creating lift that counteracts gravity. Multirotor drone propellers, such as hexacopter, octocopter, and quadcopter propellers, are arranged in pairs and rotated clockwise or anti-clockwise to keep a balance. The drone can hover, rise, descend, or change its yaw, pitch, and roll by changing the speed of these propellers. The voltage supplied to the propeller’s motor is changed to the speed of the propeller, an operation handled by an Electronic Speed Controller (ESC). The drone’s flight controller sends the right signal to the ESC, based on inputs from either the human pilot’s controller or an autopilot, and may also consider data from an IMU (Inertial Measurement System), GPS, and other sensors [14]. Hybrid VTOL UAVs combine VTOL functionality with a fixed-wing UAV’s conventional forward propulsion. Rotary lift propellers are usually included into the aircraft’s wings in many hybrids VTOL UAVs, which subsequently transition for forward flight [2, 3]. Manufacturers of drone propellers commonly include two major dimensions in the manner A × B. The first number represents the propeller’s overall length from end to end. The pitch, which is connected to the propeller’s angle and is described as how far the propeller would go forward under ideal conditions for each spin, is the second factor. Shorter propellers take less energy to accelerate to a certain speed and are easier to control and change speed due to lower inertia. Longer propellers produce additional lift for a given RPM and provide greater hovering stability, but it will demand further engine power. Propellers with a greater pitch generate more lift and allow a drone to fly faster for a given RPM, However, it will also affect the shorter battery life due to the motor demanding extra power. Heavy-lift drones will expected require much longer propellers with a smaller pitch, as stability is more crucial than the speed, and will be able to carry larger batteries or power sources, such as hydrogen fuel cells, to accommodate. There are two, three, or four bladed drone propellers are available. Propellers with more blades offer more lift per rotation since there is additional surface area moving through the air, but less efficient due to increasing drag [4]. Propellers with fewer blades are ideal for smaller drones with limited battery life. Plastic or carbon fibre propeller blades are often used in drone propellers. Plastic propellers are less expensive and more flexible than metal propellers, which allows it to absorb more impact. Carbon fibre propellers have a higher rigidity than metal propellers, in perspectives reducing vibration and hence improves the drone’s flight performance and quietness. Carbon fibre is also lighter than plastic, thus it can save total weight.

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4.3 Drone Base Frame The drone’s shape is determined by the frame, which also holds all of the subsystems in place. The frame’s most significant material property is strength, as it serves a mechanical function. Thermoplastics, including as nylon, polyester, and polystyrene variations, are attractive candidates for commercial drones because these materials are affordable to produce into complicated parts using injection molding procedures. Thermoplastics also have high tensile strength and low density, with some variants having tensile strengths of over 100 MPa and densities of less than 2 g/cm3 . Many thermoplastics are also available as filaments for 3D printing custom parts, making thermoplastics a frequent component of experimental drones. While commercial drones may afford to lose some weight in order to be more cost-effective, industrial drones put performance first. A high-strength material can be utilised in smaller quantities, resulting in a lighter, higher-performance drone. In addition to seek a material for the lowest-density and highest-strength, carbon fibre-reinforced composites are the best option for high-performance drone frames. To produce light, rigid drone frames, these materials offer great strength, low density, and high stiffness.

5 Materials for Drone Arm 5.1 Carbon Fiber Carbon Fiber, often known as graphite fiber, is a type of polymer. It is an extremely robust and lightweight material. Carbon fiber is five times stronger and two times stiffer than steel. Carbon fiber is stronger and stiffer than steel, but it is also lighter, constructing toward perfect production material for a variety of items. These are just a handful of the reasons many engineers and designers prefer carbon fiber for manufacturing. High stiffness, good tensile strength, low weight, high chemical resistance, high temperature tolerance, and minimal thermal expansion are only a few of the benefits of carbon fibers [5, 6]. Carbon fiber is widely used in aircraft, civil engineering, military, and motorsports, as well as other competitive sports, due to its unique properties. However, when compared to similar fibers such as glass or plastic fibers, carbon fibre are quite pricey. Carbon fiber is made up of a long chain of carbon atoms bonded together. The fibers are stiff, robust, and light, and are utilised in various of processes to make high-quality building materials. Carbon fiber material is available in a range of “raw” building pieces, including yarns, unidirectional, weaves, braids, and a variety of others, all of which are used to make composite parts. Carbon fiber parts have characteristics similar to steel and have a weight similar to plastic. Carbon fiber parts have a substantially greater strength to weight ratio (as well as stiffness to weight ratio) than steel or plastic parts. Carbon fiber is a very strong material [7, 8].

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The strength-to-weight ratio of carbon fiber is extremely high also known as specific strength [8]. The force per unit area at failure divided by the density of a material is its strength. A good strength-to-weight ratio can be found in any material that is both strong and light. Materials with good strength-to-weight ratios include aluminium, titanium, magnesium, carbon and glass fiber, and high-strength steel alloys. The Young Modulus, E of a material evaluates how much it deflects under stress and is used to determine its rigidity or stiffness. Carbon fiber reinforced plastic is more than four times stiffer than glass reinforced plastic, over twenty times stiffer than pine, and 2.5 times stiffer than aluminium [2, 8, 9]. Carbon fibre is chemically stable and corrosion resistant. Although carbon fibre does not decay in the presence of sunshine, Epoxy is photosensitive and must be covered. Other matrices (in which the carbon fibre is embedded) could be reactive as well [8]. Carbon fibre is a great conductor of electricity [8]. This feature can be both useful and inconvenient. It must be considered in drone construction; just as aluminium conductivity must be considered. Galvanic Corrosion in fittings can be aided by carbon fibre conductivity. This issue can be mitigated by careful installation. Carbon Fiber has excellent tensile strength and fatigue resistance [8]. Carbon Fiber Composites have a high fatigue resistance. When carbon fiber fails, however, it usually fails spectacularly with little warning of impending failure. Damage in tensile fatigue is reflected as a decrease in stiffness as the number of stress cycles increases (unless the temperature is high) When cyclic stresses coincide with fiber orientation, failure is unlikely to occur, according to tests.

5.2 Aluminium Wrought and cast aluminium alloys are the two types of aluminium alloys. The former is made up of alloys that have been melted in a furnace and then poured into moulds, whereas the later is made up of alloys that have been treated solidly. Heat-treatable and non-heat-treatable aluminium alloys can be classed based on the strengthening operating conditions. The Aluminum Association Inc. divides wrought alloys into nine series using a four-digit method, with each series consisting of distinct alloying addition combinations. The first digit (Xxxx) denotes the main constituent alloy, whereas the second digit (xXxx) denotes the original alloy’s modifications. The last two digits (xxXX) are arbitrary numbers that can be used to identify a specific alloy in the series [10]. As a result, the material qualities might change, providing a variety of application alternatives. The structural response of aluminium alloys has been studied mostly in wrought alloys, particularly the 5xxx and 6xxx series, which are the most appealing for structural engineering applications due to their mechanical properties. In order to provide more information about the manufacturing treatment, the alloy classification is followed by the temper indication. The temper designation is made up of five basic

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tempers: F (fabricated), O (annealed), H (strain-hardened), W (solution heat treated), or T (thermally treated), with extra digits indicating further information about the manufacturing treatment. Aluminium is one of the most important engineering materials of our day because of its light weight, durability, and functionality. Aluminium may be found in our homes, automobiles, trains and planes that transport us over vast distances, mobile phones and computers that always been use on a daily basis, shelves within our refrigerators, and current interior designs, yet only 200 years ago, nothing was known about this metal. Aluminium possesses a unique set of desirable characteristics. It is one of the lightest metals in the world, almost three times lighter than iron, yet it is also incredibly strong, extremely flexible, and corrosion resistant due to an extremely thin but extremely strong oxide film covering its surface. Aluminium is a non-magnetic steel, but it is a reliable conductor of electricity and can make alloys with almost any other metal.

6 Summary In summary, carbon fibre composites and aluminium are quite beneficial in the production of drone arm. Because of its malleability, carbon fibre and aluminium hollow may be easily to reached out since the industry already placed it in the market. Carbon fibre, it has a high percentage of carbon atoms, which provides it exceptional tensile strength, stiffness, and light weight. It also has excellent chemical resistance, extending its longevity. For aluminium, it is a highly versatile metal that offers a lot of benefits, including being lightweight and flexible. The speciality of an aluminium is it can be cast, melted, moulded, machined, and extruded, allowing it to be moulded into a variety of shapes and then built to fit a wide range of applications. Finally, carbon fibre composites and aluminium are the future of drone manufacturing, as titanium and steel are increasingly phased out. Acknowledgements The research was supported by Universiti Tun Hussein Onn Malaysia (UTHM) through Tier 1 UTHM (Vot H773) and Geran Kontrak UTHM (H870).

References 1. Leishman JG, Johnson B (2009) Engineering analysis of the 1907 cornu helicopter. J Am Helicopter Soc 54.https://doi.org/10.4050/jahs.54.034001 2. Mazlan NEA, Shamsudin SS, Pairan MF et al (2021) The design of an automatic flight control system and dynamic simulation for fixed-wing unmanned aerial vehicle (UAV) using X-Plane and LabVIEW. Prog Aerosp Aviat Technol 1:56–69 3. Shamsudin SS, Madzni MZ (2021) Aerodynamic analysis of Quadrotor UAV propeller using computational fluid dynamic. J Complex Flow 3:28–32

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4. Christodoulou K, Vozinidis M, Karanatsios A, et al (2019) Aerodynamic analysis of a quadcopter drone propeller with the use of computational fluid dynamics. Chem Eng Trans 76. https://doi.org/10.3303/CET1976031 5. Hamidon MH, Sultan MTH, Ariffin AH (2019) Investigation of mechanical testing on hybrid composite materials. In: Jawaid M, Thariq M, Saba Fibre-Reinforced Composites and Hybrid Composites NBT-FA in B (eds) Woodhead publishing series in composites science and engineering. Woodhead Publishing, pp 133–156 6. Ismail KI, Sultan MTH, Shah AU, et al (2018) Tensile properties of hybrid biocomposite reinforced epoxy modified with Carbon Nanotube (CNT). BioResources 13. https://doi.org/ 10.15376/biores.13.1.1787-1800 7. Mallick PK (2008) Fiber reinforced composites: materials, manufaturing and design 8. Bhatt P, Goe A (2017) Carbon fibres: production, properties and potential use. Mater Sci Res India 14:52–57. https://doi.org/10.13005/msri/140109 9. Georgantzia E, Gkantou M, Kamaris GS (2021) Aluminium alloys as structural material: a review of research. Eng Struct 227 10. Chen DC, You CS, Gao FY (2014) Analysis and experiment of 7075 aluminum alloy tensile test. Procedia Eng

Characterization of Semi Amorphous Phase of Rice Husk Silica Reinforced AA7075 Aluminium Chips Based Matrix Hoo Wei Wen, Noradila Abdul Latif, Nurul Farahin Mohd Joharudin, and Mohammad Sukri Mustapa

1 Introduction Aluminum alloys have been widely used in automotive and aerospace industries, owing to their low density, high specific strength and high thermal conductivity, which leads to the weight reduction and economic advantage [1, 2]. Aluminium is over three times lighter than steel, but it needs a lot of energy for production. However, their relatively low hardness and poor wear resistance are the main disadvantage and obstacles for their high-performance applications [3]. Metal matrix composite is one type of composite material in which a strong ceramic reinforcement is incorporated into a metal matrix to improve its properties including high strength and stiffness, resistance to wear, corrosion resistance and high elastic modulus [3, 4]. Aluminium and its alloys are the most common base metal in metal matrix composites. Aluminium oxide and silicon carbide are the most frequently used as reinforcement in aluminium matrix composites [5]. Recycled aluminium is one of the methods by which scrap aluminium can be reprocessed in other products after its initial production. Due to some economic and environmental reasons, recycling of aluminium is extremely important. Recycling aluminium saved around 95% of energy compared to primary aluminium [6, 7]. Due to the growing interest in aluminium metal, waste has become one of the most popular issues, despite the fact that the majority of aluminium used today comes from recycled automotive components. New solid state recycling techniques have been considered H. W. Wen · N. F. M. Joharudin Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Johor, Malaysia N. A. Latif (B) · M. S. Mustapa Mechanical Failure Prevention and Reliability Research Centre (MPROVE), Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Johor, Malaysia e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_12

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since global warming of concern [8]. This recycling method employing compression and extrusion at room can affect significant energy savings compared to re-melting recycling aluminium. Composite materials consist of reinforcement and matrix. The use of composite materials evolves mainly in engineering [4]. The reinforcement provides the strength and stiffness which normally have the properties of harder, stiffer, and stronger than the matrix. Reinforcement is usually a fibre or a particulate. The addition of reinforcement in aluminium matrix composites improves its mechanical properties included strength, hardness and density [9]. Hard reinforcement such as fibres, silica and whiskers are introduced into Aluminium based matrix form to improve their physical and mechanical properties such as strength [10]. These materials offer great opportunities for advanced material and development. Rice husks is an agricultural waste which provides an abundant silica source due to the sodium silica content in the ash of rice husk. Rice husks generated from rice mills usually cause disposal problems and it usually burnt and disposed without being put to good use [11]. Rice husk ash with rich silica content produced by burning the rice husk. Burning rice husk can leaves about 25% of rice husk ash. The characteristics of rice husk ash are dependent on three factors which are the composition rice husk, burning temperature and burning time [12, 13]. Based on investigation, rice husk ash is a potential reinforcing agent that can replace other conventional silica sources due to its high silica content. Semi amorphous silica was obtained at 900 °C and 1000 °C firing temperature which in transitional phase [14]. The hardness and compression strength will also improve by adding reinforcement of rice husk silica into aluminium alloy AA7075. Therefore, the AA7075 aluminium chips reinforced with rice husk silica for composite can reduce the waste by changing it into valuable raw material, where aluminium matrix composites are valuable to manufacture by improved the properties of recycle aluminium and reducing cost.

2 Experiment Procedure 2.1 Based Matrix of AA7075 Aluminium Chips AA7075 aluminium alloy chips was used as the based matrix of AMC. The chemical composition of AA7075 aluminium alloy in mass fraction (wt%) is listed in Table 1. The mechanical properties of AA7075 aluminium alloy are listed in Table 2. Table 1 The chemical composition of AA7075 aluminium alloy (wt%) Al

Zn

Cu

Si

Cr

Others

87.18

9.49

2.59

0.31

0.28

0.15

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Table 2 The mechanical properties of AA7075 aluminium alloy [15] Properties

Value

Density (g/cm3 )

2.8

Tensile Strength (MPa)

230

Yield Strength (MPa)

105

Hardness (HB500)

60

Shear strength (MPa)

150

Fatigue strength (MPa)

160

Table 3 The parameters of milling for preparation of AA7075 aluminium chips Parameters

Parameters set up

Machine name

Mazak Nexus 410A-II CNC Mill

Tool

10 mm diameter, 2 flute carbide

Feed rate

1100 mm/min

Depth of cut

1 mm

Speed

345 m/min

The preparation of AA7075 aluminium chips by milling process is followed to parameters listed in Table 3. The chips were then cleaned by using an ultrasonic bath apparatus, FRITSCH using acetone solution with duration of 1 h to remove any impurities. The aluminium chips were drying using oven with temperature of 75 °C for 1 h to remove the residual of acetone solution from the chips [16–18].

2.2 Rice Husk Silica Reinforced Aluminium Based Matrix Composite The reinforcement used which is rice husk was obtained from a local industry, Nano Siltech Sdn. Bhd. Rice husk was treated by burning rice husk by temperature of 1000 °C under semi-amorphous phase to form rice husk ash. By the X-ray fluorescence (XRF) test, the chemical composition of rice husk ash obtained, and it was listed in Table 4. Found that the significant element in rice husk ash was silica content, where it could be called as semi amorphous rice husk silica or rice husk silica. Table 4 The chemical composition of rice husk silica at 1000 °C (wt%) SiO2

K2 O

P2 O5

SO3

Al2 O3

Ci

CaO

MgO

Others

91.07

2.87

1.70

1.14

0.87

0.68

0.64

0.58

1.46

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Table 5 The composition of AMC specimens Specimens

AA7075 aluminium chip (wt%)

Rice husk silica (wt%)

100 wt% AA7075

100

0

97.5 wt% AA7075 + 2.5 wt% RHA

97.5

2.5

95.0 wt% AA7075 + 5.0 wt% RHA

95.0

5.0

92.5 wt% AA7075 + 7.5 wt% RHA

92.5

7.5

90.0 wt% AA7075 + 10.0 wt% RHA

90.0

10.0

87.5 wt% AA7075 + 12.5 wt% RHA

87.5

12.5

2.3 Preparation of AMC Specimens Mixing process was performed by using the ball mill machine to blend all the materials in randomly ordered to each other. Weight percentages of rice husk silica and aluminium alloy chips with different mass fraction for preparing AMC specimens are shown in Table 5. In addition, 1% of zinc stearate was also added into each specimen for acting as a binder. The compaction method was conducted using the uniaxial hydraulic press machine. The specimens were poured into the round mould with 13 mm diameter to shape the specimen. The setting load and holding time of cold compaction process were 9 tons and 20 min, respectively [19, 20].

2.4 Sintering Process Sintering process was performed to reduce the porosity and enhances properties such as strength. This process was conducted by using tube furnace under an argon atmosphere. An argon gas was turned on for 1 h before starting the process to make sure that tube furnace is fully saturated by argon gas. The temperature held at 300 °C for 30 min to remove the binder, then increasing with the rate of 5 °C/min to sintering temperature of 552 °C and hold for 60 min [21].

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2.5 Analysis of Specimens The mechanical tests included microhardness by following the standard ASTM E384 and compression test by following the standard ASTM E9 to determine and analyse the mechanical properties of specimens. The length of round specimens used was 25 mm which the ratio of height to diameter less than 2 to avoid buckling action occur during compression test. Vickers tester was used to determine the hardness value of the specimen. The setting of the tester was 980.7 mN of load with 10 s of duration. Universal Testing Machine (UTM) with 100 kN maximum capacity of loadcell and cross head speed of 1 mm/min was used to perform the compression test. Physical tests were conducted to determine the physical properties included density (g/cm3 ), porosity (%) and water absorption (%). The tests conducted using Archimedes principle by using density kit followed the standard ASTM B328 for density and ASTM B962-17 for the porosity. Optical microscope with a model of Olympus BX60M was used to observe the microstructure of the AMC specimens. The image was captured in lower magnification of 50 times on the specimens to observe the new microstructure arrangement after addition of rice husk silica.

3 Result and Discussion 3.1 X-ray Diffraction (XRD) Analysis Rice husk silica that burned at 1000 °C in furnace box and sieved to 63 μm of particle size was conducted the X-ray diffraction test. Figure 1 shows the result that analysed by EVA software. Sample of rice husk silica contained three type phases of SiO2 which are cristobalite, tridymite and quartz where the most match phases is quartz phase. The quartz phase of silica dioxide when it burned to 1000 °C called β-quartz which is hexagonal structure [22]. The sample of rice husk silica is the mixture of amorphous and crystalline due to it does not produce sharp diffraction peaks. However, the crystalline characteristic in diffraction graph increases from original rice husk as showed in Fig. 2. It can conclude that the sample of rice husk silica is in state of semi amorphous.

3.2 Microhardness of Aluminium Matrix Composites Figure 3 shows the microhardness of aluminium matrix composite specimens. It shows that the increment of hardness value with increasing the percentage of rice husk silica reinforcement from 5.0 to 10 wt%. The highest hardness of AMC of 68.33 Hv increased at 55.54% when compared to 100% AA7075 aluminium chips.

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Fig. 1 X-ray diffraction graph for rice husk silica burned at 1000 °C

Fig. 2 XRD graph for original rice husk and rice husk ash burned at 1000 °C

The silica content of rice husk had improved the hardness of the AMC specimens. However, the stiffness of aluminium matrix composites was slightly decreased with increasing of composition of silica at 12 wt%. Mohd Joharuddin et al. (2020) reported the hardness of AMC was increased with increasing the composition of rice husk ash up to 65.93 Hv for untreated rice husk ash and 69.56 Hv for treated rice husk

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ash at composition of 10 wt%. Meanwhile, the hardness of aluminium chips without reinforcement was 53.49 Hv [16]. In general, the increase of hardness of a material means that the surface of the material offers more resistance to plastic deformation. Figure 4 shows the indentation of few specimens with different composition of rice husk silica in micrograph from the microhardness test. The indentation size at specimen contains 10 wt% of rice husk silica become smaller when added high rice husk silica for the composite. The presence of rice husk silica reinforcement led to strengthen the AMC due to the increased hardness values.

Fig. 3 Microhardness (Hv) with the increasing in mass fraction of rice husk silica (wt%)

Fig. 4 Micrograph of indentation from microhardness test; a 100 wt% of aluminium chips, b 5 wt% of rice husk silica, c 10 wt% of rice husk silica

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3.3 Compression Strength of Aluminium Matrix Composites In Fig. 5, all the aluminium matrix composites showed similar trend of stress–strain curves while the 100 wt% aluminium specimens had smaller gradient and higher strain value. Table 6 is the list of compression properties for aluminium matrix composites. The compression strength for rice husk silica with more than 10 wt.% reinforced aluminium based matrix were decreased as listed in Table 6. For ultimate compression strength, three AMC specimens which are the composition of 2.5 wt%, 5.0 wt% and 7.5 wt% rice husk silica had higher strength values compared to 100 wt% of aluminium specimen. However, the compression strength for 10.0 wt.% and 12.5 wt.% composition of rice husk silica was much lower compared to 100 wt% of aluminium specimens. This can conclude that the presence of rice husk silica in aluminium chip by composition of 2.5–7.5 wt% had improved the behavior of the AMC to withstand loads before failure. The highest ultimate compression strength is 312.63 MPa which improved 6.68% compared to 100 wt% of recycled aluminium specimen. Strain is the amount of deformation an object undergoes due to force or stress and it is the physical effect of that force on the specimen. From Table 6, the aluminium matrix composites reinforced with rice husk silica had lower strain value compared to 100 wt% of aluminium alloy. The strain for all aluminium matrix composites from 2.5 to 12.5 wt% of rice husk silica composition had almost similar strain values. The elastic modulus can be related to the stiffness of a material. A high stiffness material will have a higher elastic modulus. All the aluminium matrix composites had higher elastic modulus compared to 100 wt.% aluminium alloy which showed in Table 6. It means that the presence of rice husk silica in aluminium matrix composites lead to increase the stiffness of the AMC and the highest elastic modulus was 1089.58 MPa for 2.5 wt% of rice husk silica composition. However, elastic modulus decreases when the rice husk silica composition increases with more than 10.0 wt%.

Fig. 5 Stress–strain graph of compression aluminium matrix composites

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Table 6 Compression properties of aluminium matrix composites Specimens

Ultimate compression strength (MPa)

Strain (%)

Elastic modulus (MPa)

100 wt% AA7075

293.06

37.53

780.87

97.5 wt% AA7075 + 2.5 wt% RHA

310.53

28.50

1089.58

95.0 wt% AA7075 + 5.0 wt% RHA

308.15

29.05

1060.76

92.5 wt% AA7075 + 7.5 wt% RHA

312.63

30.22

1034.51

90.0 wt% AA7075 + 10.0 wt% RHA

261.84

26.89

973.74

87.5 wt% AA7075 + 12.5 wt% RHA

244.22

26.85

909.57

3.4 Physical Properties of Aluminium Matrix Composites The physical properties of density, porosity and water absorption of each composition of aluminium matrix composites reinforced with rice husk silica have been obtained. Table 7 lists the result of physical properties of AMC specimens. Figure 6 shows the physical properties trend graph of aluminium matrix composites. The density of the AMC had a significant changed by increasing the composition of rice husk silica as reinforcement compared to the 100 wt% aluminium alloy. Density of aluminium matrix composites increased by increasing the composition of semi amorphous of rice husk silica. It can be concluded that the density of aluminium matrix composites was significantly dependent to the composition of rice husk silica. However, Mohd Joharuddin et. al. (2020) reported the density of AMC rapidly increased at increasing the addition of rice husk ash up to 5 wt%. Subsequently, the density of AMC was decreased at more than 5 wt% of rice husk ash composition. So that, when the density decreased, thus the porosity was increased to give the reason of weak bonding of the untreated and treated reinforced particles at more composition in AMC [16]. Table 7 Physical properties of aluminium matrix composites Specimens

Density (g/cm3 )

Porosity (%)

Water absorption (%)

100 wt% AA7075

2.1901

0.4197

0.3514

97.5 wt% AA7075 + 2.5 wt% RHA

2.2557

0.3851

0.3057

95.0 wt% AA7075 + 5.0 wt% RHA

2.3014

0.4015

0.3076

92.5 wt% AA7075 + 7.5 wt% RHA

2.2478

0.4193

0.3349

90.0 wt% AA7075 + 10.0 wt% RHA

2.3064

0.4119

0.3143

87.5 wt% AA7075 + 12.5 wt% RHA

2.2844

0.3931

0.3052

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Fig. 6 The trend graph of physical properties of aluminium matrix composites

The analysis of porosity is to measure the void spaces in a material. The porosity of aluminium matrix composites reinforced with rice husk silica are very low. This obeyed the maximum permissible porosity that less than 4 wt% in cast metal matrix composites [23]. The results were similar trend to the water absorption. Water absorption is used to determine the amount of water that absorbed by the material under specified conditions. All the AMC specimens had low percentage of water absorption. The porosity and water absorption of aluminium matrix composites were independent to the composition of rice husk silica.

3.5 Microstructure of Aluminium Matrix Composites Microstructure observation was conducted after mounting, grinding and polishing all the AMC specimens. The AMC specimens of 15 mm height and 13 mm diameter were prepared and used. By using optical microscope, the chip size, orientation and shape can be identified. The images of the microstructure were captured at 50× magnification for all AMC specimens. Figure 7 shows the microstructure of 100 wt% of aluminium chips and aluminium matrix composites reinforced semi amorphous of rice husk silica from the composition of 2.5 wt% to 12.5 wt%. From the Fig. 7, the pores for 100 wt% of recycle aluminium chip specimen are significant and larger size. This is due to the larger size of aluminium chips are used in this experiment. The pores for aluminium AA7075 composite reinforced rice husk silica showed significantly reduce in size and its shapes. The reinforcement rice husk silica filled up the gaps of aluminium chips AA7075. This proved that adding more powder particles into the specimens, it resulted in smaller average pore size, less pores formation and more spherical pore shape [19]. The 100 wt% of aluminium specimen also showed the largest size of chip boundary while the size decreases when the composition of rice husk silica increase. There is much more chip boundary for higher composition of rice husk silica specimens. It illustrates fair amount of chip

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Pores

Chip Boundary

a) 100 wt.% AA7075

b) 97.5 wt.% AA7075 + 2.5 wt.% RHA

Pores

Chip Boundary

c) 95.0 wt.% AA7075 + 5.0 wt.% RHA

d) 92.5 wt.% AA7075 + 7.5 wt.% RHA

Pores

Chip Boundary

e) 90.0 wt.% AA7075 + 10.0 wt.% RHA

f) 87.5 wt.% AA7075 + 12.5 wt.% RHA

Fig. 7 Microstructure of aluminium matrix composites at 50× magnification

boundary due to the smaller size of rice husk silica powder to the size of aluminium chips. The smaller size of chip boundary will result higher hardness value [24].

4 Conclusion The conclusion of this study as follows: (a) Rice husk ash that generated from rice milling process is a potential material act as reinforcement in AMC, where semi amorphous rice husk silica obtained after burning the as-received non-chemical rice husk at temperature of 1000 °C.

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(b) The mechanical properties of aluminium matrix composites such as hardness and compression strength were improved than 100 wt% of aluminium alloy. (c) The optimum composition of rice husk silica in aluminium chip AA7075 is at 10 wt% for hardness, while the highest compression strength is at 7.5 wt% of rice husk silica. (d) The porosity and water absorption of aluminium matrix composites were independent to the composition of rice husk silica while, density of AMC was dependent to the addition of rice husk silica. Acknowledgements This research was supported by the Ministry of Higher Education (MOHE) through Fundamental Research Grant Scheme (FRGS/1/2018/TK03/UTHM/03/17). We also want to thank the Universiti Tun Hussein Onn Malaysia for sponsoring this work under research grant No. K067.

References 1. Mostafa AM, Hameed MF, Obayya SS (2019) Effect of laser shock peening on the hardness of AL-7075 alloy. J King Saud Univ Sci 31(4):472–478 2. Mazahery A, Shabani MO (2012) Mechanical properties of A356 matrix composites reinforced with nano-SiC particles. Strength Mater 44:686–692 3. Zhai W, Bai L, Zhou R, Fan X, Kang G, Liu Y, Zhou K (2021) Recent progress on wear-resistant materials: designs, properties, and applications. Adv Sci 8:2003739 4. Sharma AK, Bhandari R, Aherwar A, Rimašauskien˙e R (2020) Matrix materials used in composites: a comprehensive study. Mater Today Proc 21(3):1559–1562 5. Bodunrin MO, Alaneme KK, Chown LH (2015) Aluminium matrix hybrid composites: a review of reinforcement philosophies; mechanical, corrosion and tribological characteristics. J Mater Res Technol 4(4):434–445 6. Abdel-Shafy HI, Mansour MSM (2018) Solid waste issue: sources, composition, disposal, recycling, and valorization. Egypt J Petrol 27(4):1275–1290 7. Brough D, Jouhara H (2020) The aluminium industry: a review on state-of-the-art technologies, environmental impacts and possibilities for waste heat recovery. Int J Thermofluids 1–2:100007 8. Singh N, Hui D, Singh R, Ahuja IPS, Feo L, Fraternali F (2017) Composites Part B: Engineering, 2017, 115:409–422 9. Alaneme KK, Fajemisin AV, Maledi NB (2019) Development of aluminium-based composites reinforced with steel and graphite particles: structural, mechanical and wear characterization. J Mater Res Technol 8(1):670–682 10. Mazahery A, Abdizadeh H, Baharvandi HR (2009) Development of high-performance A356/nano-Al2 O3 composites. Mater Sci Eng A 518(1–2):61–64 11. Sharifnasab H (2017) Preparation of silica powder from rice husk. Agr Eng IntCIGR e-J 19(1):158 12. Hossain SKS, Mathur L, Roy PK (2018) Rice husk/rice husk ash as an alternative source of silica in ceramics: a review. J Asian Ceram Soc 6(4):299–313 13. Kamweru P, Gichumbi J, Ndiritu F, Jonathan K (2020) Characterization of rice husk ash prepared by open air burning and furnace calcination. J Chem Eng Mater Sci 11:24–30 14. Joharudin NFM, Latif NA, Mustapa MS, Badarulzaman NA, Mahmod MF (2020) Effect of burning temperature on rice husk silica as reinforcement of recycled aluminium Chip AA7075. J Adv Res Fluid Mech Therm Sci 68(1):125–132

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15. Persson EL (2011) Aluminum alloys: preparation, properties, and applications (Ser. Materials science and technologies). Nova Science Publishers. Retrieved 27 June 2021 16. Joharudin NFM, Latif NA, Mustapa MS, Badarulzaman NA (2020) Effects of untreated and treated rice husk ash (RHA) on physical properties of recycled aluminium chip AA7075. Int J Integr Eng 12(1):132–137 17. Mustapa MS, Mahdi AS, Lajis MA, Abd Rashid MW (2015) Physical properties of recycling milled aluminium chip (AA6061) for various sintering temperature. Int J Mech Ind Technol 3(2):33–40 18. Mahdi AS, Mustapa MS, Latif NA, Ab Kadir MI, Samsi MA (2017) Heat treatment for an recycling aluminum AA6061 using milling process at various holding aging time. Int J Eng Technol (IJET) 8:2582–2587 19. Kadir MIA, Mustapa MS, Ibrahim MR, Samsi MA, Mahdi AS (2017) Microstructures and characteristics of solid-state recycling aluminium chips AA6061/Al-SiC composites fabricated by cold compaction method. In: AIP conference proceedings, vol 1846, no 1, p 020005 20. Joharudin NFM, Latif NA, Mustapa MS, Mansor MN, Siswanto WA, Murugesan J, Yusof F (2019) Effect of amorphous silica by rice husk ash on physical properties and microstructures of recycled aluminium chip AA7075. Materialwissenschaft und Werkstofftechnik 50(3):283–288 21. Kadir MIA, Mustapa MS (2018) The effect of microstructures and hardness characteristics of recycling aluminium chip AA6061/Al powder on various sintering temperatures. Int J Integr Eng 10(3):53–56 22. Guthrie GD, Heaney PJ Jr (1995) Mineralogical characteristics of silica polymorphs in relation to their biological activities. Scand J Work Environ Health 21(2):5–8 23. Alaneme KK, Sanusi KO (2015) Microstructural characteristics, mechanical and wear behaviour of aluminium matrix hybrid composites reinforced with alumina, rice husk ash and graphite. Eng Sci Technol Int J 18(3):416–422 24. Li J, Lu Y, Zhang H, Xin L (2015) Effect of grain size and hardness on fretting wear behavior of Inconel 600 alloys. Tribol Int 81:215–222

Improving the Flexural and Tensile Properties of Reinforced Polypropylene Composites by Using Pineapple Leaf Fibre Syafiqah Nur Azrie Safri, Muhammad Naim Romzee, Muhammad Adli Zufayri Shamsol, Ahmad Hamdan Ariffin, Fairuz Alias, Mohamad Norani Mansur, Mohammad Sukri Mustapa, Irfan Abdul Rahim, and Mohd. Fadhli Zulkafli

1 Introduction Pineapple, scientifically known as Ananas Comoscus commonly found in Africa, South Central America, and Asia. Pineapple is the third most grown fruit, behind bananas and citrus fruits. Pineapple leaves are widely regarded as waste due to roughly forty to fifty leaves per stalk, increasing the volume of post-harvest rubbish. The plant has a short stem and approximately eighty leaves of various shapes and lengths on a fully matured pineapple. According to their structure, the vascular bundles, which are found beneath the top lamina, and the finer fibre, which is located beneath the bottom lamina, are two types of fibre found in pineapple leaves. These leaves have low microfibrillar angles and high cellulose content, resulting in better S. N. A. Safri (B) · A. H. Ariffin (B) · Mohd. F. Zulkafli Research Centre for Unmanned Vehicle (ReCUV), Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia e-mail: [email protected] A. H. Ariffin e-mail: [email protected] M. N. Romzee · M. A. Z. Shamsol · A. H. Ariffin · F. Alias · M. N. Mansur · M. S. Mustapa · Mohd. F. Zulkafli Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia I. A. Rahim Faculty of Mechanical Engineering Technology, Universiti Malaysia Perlis, Kampus Tetap Pauh Putra, 02600 Arau, Perlis, Malaysia A. H. Ariffin · I. A. Rahim Green Design and Manufacture Research Group, Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Universiti Malaysia Perlis, 01000 Kangar, Perlis, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_13

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mechanical qualities for their fibres [1]. Pineapple leaves are processed mechanically or by retting in water to extract the fibre. Pineapple leaves have a strong, white silky fibre that hasn’t been graded due to the tiny amount of fibre present [2]. Previous studies emphasized that pineapple leaf fibre (PALF) possesses outstanding mechanical properties compared to other natural fibres due to its lignocellulosic and multicellular characteristics [3]. A series of recent studies have indicated that PALFs are suitable and effective reinforcement for polyester matrix composites because the fibres help improve mechanical properties. Previous results show that the strength and elastic modulus of polyester matrix composites increased after adding PALF to the composite. The results successfully indicated excellent flexural results from PALF polyester matrix composites compared to other materials with same the matrix composition [4]. Senthilkumar et al. [5] found an improvement in mechanical and dynamic characteristics of composites made with 35 wt.% PALF, and it can be used in low-strength applications. Previous studies have shown that PALF is produced in enormous quantities each year, but only a small percentage of this fibre is employed as raw material in the industrial process. Even though the pineapple plant is one of the most popular tropical plants with a vast range of options, many agricultural enterprises only use the plant’s fruit and discard the leaves, which can pollute the air when burned. Due to a lack of understanding and awareness about these leaves’ fibre, it is impossible to utilize all their benefits and potential fully. This research aims to investigate the compatibility of the PALF with polypropylene to cut down on the amount of wasted pineapple leaves produced by agricultural businesses. This research investigates the tensile and flexural properties of PALF/PP composites by studying the influence of PALF weight percentage (wt.%) in PP composites.

2 Methodology 2.1 Composition Analysis The lignin, cellulose, and hemicellulose content were analyzed by the Malaysian Agricultural Research and Development Institute (MARDI). Two different Technical Association of Pulp and Paper Industry (TAPPI) standards were used to investigate the percentage of lignin, cellulose, and hemicellulose in the sample, which are T222 OS-83 and T203 OS-74.

2.2 Fabrication Using Injection Moulding Two materials will be used in the mixing process: PALF and polypropylene (PP). These materials will be combined in the Roll Mill Mixer machine in the Polymer Lab

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Table 1 Composition of the fabricated sample Sample

Weight percentage of PALF (wt.%)

Weight percentage of PP (wt.%)

Pure PP

0

100

2%PALF + 98%PP

2

98

4%PALF + 96%PP

4

96

6%PALF + 94%PP

6

94

Fig. 1 Sample size for tensile testing according to ISO 527

at the Faculty of Mechanical and Manufacturing Engineering, UTHM. The machine must be set to 190 °C and 350 RPM for 30 min to achieve a mixture size of 63 µm. Table 1 shows the composition of the samples for both tensile and flexural tests. The materials will be weighed as in Table 1 before being loaded into the Roll Mill Mixer equipment and mixed thoroughly for 20 min. After the PALF and PP have been mixed, the mixture will be crushed using Plastic Granulator Crusher Machine since the sample must be pallet-sized to fit perfectly in the Injection Moulding machine. The pallets will be melted down during the Injection Moulding process to fill the mould cavity and produce the specimen shape. The melted polymer composite will then be compressed using the Injection Moulding machine with a rectangular-shaped mould. The specimen will be made in accordance with the ISO 527 standard (Fig. 1) for the tensile test and the ASTM D790-03 standard for the flexural test. Throughout this process, the Injection Moulding machine will be set to 190 °C, and the specimen will need to cool down for about 10 min.

2.3 Tensile and Flexural Test Tensile test was performed following the IS0 527 standard, using a Universal Testing Machine located in the Polymer Lab at the Faculty of Mechanical and Manufacturing Engineering, UTHM. The flexural test was performed with a 3-point loading on a Universal Testing Machine in the Polymer Lab at the Faculty of Mechanical and

208 Table 2 Chemical composition of PALF

S. N. A. Safri et al. Composition Lignin

Percentage of composition (%) 4.75

Cellulose

59.72

Hemicellulose

20.06

Manufacturing Engineering, UTHM, in accordance with ASTM D790-03. Injection moulding was used to create rectangular samples with dimensions of 4 mm thickness and 9 mm width. The experiment was carried out at a crosshead displacement rate of 5 mm/min. Six specimens were tested at room temperature for each weight ratio for both tensile and flexural tests, and the average was used as the final result.

3 Results and Discussions 3.1 Chemical Composition of PALF Table 2 shows the chemical composition of PALF used in this research. Previous studies showed that the chemical composition of PALF varies depending on the region and variant studied [6]. PALF planted in Indonesia had 70.51% cellulose content [7], PALF made from the Yankee variant had 47.74% of cellulose content [8] and PALF used in this research had 59.72% of cellulose content. Previous research also shows that the values for NDF (lignin, cellulose, cell wall protein, silica and hemicellulose) and NDS (lipid, protein, carbohydrate, pectin) for Hawaiian pineapple leaf is 64.9 and 35.1% different than Thai pineapple leaf [9]. One factor that adds to the fibre’s tensile strength is the presence of cellulose within the fibre. The fibre was composed primarily of cellulose, followed by hemicellulose and lignin. Lignin (dry matter accounting for 5–30%) and hemicellulose (dry matter accounting for 20–35%) were typically wrapped by cellulose [10].

3.2 Tensile Properties Table 3 and Fig. 2 shows the tensile properties of all tested specimen, Pure PP, 2%PALF + 98%PP, 4%PALF + 96%PP, and 6%PALF + 94%PP composites. The maximum force value is also known maximum total load needed for the composite to break. The results in Table 3 show that more force is required for the specimen to break after PALF is incorporated into the PP composite. The main reason is that the force is distributed to the fibre equally. Thus, more force is required to break the sample. Increasing the PALF wt.% from 0 to 6% in the sample led to an increase in maximum force by 6.46%. Maximum displacement from tensile testing shows the

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Table 3 Tensile properties of pure PP and PALF/PP composites Sample

Maximum force (N)

Maximum displacement (mm)

Maximum strain (%)

Pure PP

197.31

3.46

17.30

2%PALF + 98%PP

193.30

2.79

13.94

4%PALF + 96%PP

206.09

2.83

14.16

6%PALF + 94%PP

210.06

2.71

13.57

180

21.5

Tensile Strength (MPa)

140 20.5

120

20

100 80

19.5

60

19

40 18.5

Young Modulus (MPa)

160

21

20 0

18 Pure PP

2%PALF + 98%PP

4%PALF + 96%PP

6%PALF + 94%PP

Sample Tensile Strength (MPa)

Young Modulus (MPa)

Fig. 2 Tensile strength and tensile modulus of pure PP and PALF/PP composites

elongation that the composite can experience during the testing. It was found that the composite made from pure PP elongates more before it breaks. This shows that composite made from pure PP is more elastic than PALF/PP composite. PALF had acted as a barrier in the PP composite, thus making the composite less ductile than the pure PP composite. This is similar to previous research on the ductility of pineapple leaf fibres reinforced high-density polyethylene composites [11]. The elasticity of polypropylene reduces with the addition of PALF, indicating that the composite grew brittle as the wt.% increased. In general, adding pineapple leaf fibre to the pure PP composite help to increase its tensile properties. Maximum tensile stress, or ultimate tensile strength, indicates the composite resistance from the tensile force. Figure 2 shows that the ultimate tensile strength tends to increase proportionally with the ratio of PALF inside the sample. Increasing the PALF wt.% from 0 to 6% led to higher tensile strength by 6.48%. Strength was also enhanced by the presence of PALF, which carries most of the axial stress during the tensile test [12]. Tensile modulus also referred to as Young Modulus, shows the stiffness ability of the composites. From the graph, it can be seen that the value of Young Modulus increases as the PALF wt.% increase. Additionally, this enhances the capability of the PP composite to bear the tensile load. Composites made from 2%PALF + 98%PP show a decreased value in tensile

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Table 4 Flexural properties of pure PP and PALF/PP composites Sample

Maximum force (N)

Maximum displacement (mm)

Maximum strain (%)

Pure PP

51.95

11.69

7.79

2%PALF + 98%PP

55.70

11.57

7.71

4%PALF + 96%PP

53.86

11.47

7.64

6%PALF + 94%PP

57.84

10.80

7.20

properties compared to pure PP composites. This may be due to a void in the sample that often contributes to lower the experimental value [13].

3.3 Flexural Properties

37

600

36

500

35 400 34 300 33 200 32 100

31 30

0 Pure PP

2%PALF + 98%PP

4%PALF + 96%PP

6%PALF + 94%PP

Sample Flexural Strength (MPa)

Flexural Modulus (MPa)

Fig. 3 Flexural strength and flexural modulus of pure PP and PALF/PP composites

Flexural Modulus (MPa)

Flexural Strength (MPa)

Table 4 and Fig. 3 shows the flexural properties of all tested specimen, Pure PP, 2%PALF + 98%PP, 4%PALF + 96%PP, and 6%PALF + 94%PP composites. Table 4 shows that as the percentage of PALF increase, the maximum force required for the specimen to fail also increase. The maximum flexural force for pure PP composite is 51.95 N, while for 2%PALF + 98%PP composite, the maximum flexural force is 55.70 N. The value of maximum force increased as the PALF wt.% increased up to 6%. Similarly, with the previous tensile test, the maximum deformation experience by the composites decreased as the wt.% of PALF increased. This directly proves that by adding PALF to the PP composites, the tensile behaviour of the composites will be reduced due to the characteristic of the PALF. This is because

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with an increase in wt.%, the brittleness of the composite increased and created poor interfacial bonding between the PALF and PP [14]. During the bending test, the maximum flexural stress on the composite surface is also known as flexural strength. Figure 3 shows that a composite made from 6%PALF + 94%PP had 11.33% more flexural strength than pure PP composites. PP is also in the same group as thermoplastic. Thermoplastic composites are commonly known for having lower flexural strength. Therefore, by adding PALF into the pure PP composites, the flexural strength of PP composites can be increased. Similarly, all composites made from 2, 4, and 6% PALF for the flexural modulus had 8.35, 5.69, and 20.48% of the flexural modulus compared to pure PP composites. Bonding between fibre and matrix in a composite is one of the factors that can affect the composite flexural modulus. The improved flexural modulus and flexural strength prove strong bonding between the PP and PALF.

4 Conclusions The chemical, tensile and flexural properties of PALF/PP composites with various weight percentage (wt.%) were presented. The chemical properties results show that several factors affect the percentage of cellulose, hemicellulose, and lignin in the PALF. The experimental results found that the higher the weight percentage of PALF in the PP composites, the higher the tensile and flexural properties of the composites. Composites made from 6%PALF + 94%PP exhibited excellent tensile and flexural performance compared to other composites. However, adding PALF into the PP composites made the composite less ductile, which could be one of the important factors to consider before implementing the composite to any structure application. Acknowledgements The research was supported by Universiti Tun Hussein Onn Malaysia (UTHM) through Tier 1 UTHM (Vot H773) and Geran Kontrak UTHM (H870).

References 1. Todkar SS, Patil SA (2019) Review on mechanical properties evaluation of pineapple leaf fibre (PALF) reinforced polymer composites. Compos B Eng 174:106927. https://doi.org/10.1016/ J.COMPOSITESB.2019.106927 2. Mishra S, Mohanty AK, Drzal LT et al (2004) A review on pineapple leaf fibers, sisal fibers and their biocomposites. Macromol Mater Eng 289:955–974. https://doi.org/10.1002/MAME. 200400132 3. Saravanakumar M, Kumar SS, Babu BS, Chakravarthy CN (2021) Influence of fiber loading on mechanical characterization of pineapple leaf and kenaf fibers reinforced polyester composites. Mater Today: Proc 46:439–444. https://doi.org/10.1016/J.MATPR.2020.09.804 4. Glória GO, Teles MCA, Lopes FPD et al (2017) Tensile strength of polyester composites reinforced with PALF. J Market Res 6:401–405. https://doi.org/10.1016/J.JMRT.2017.08.006

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5. Senthilkumar K, Saba N, Chandrasekar M et al (2019) Evaluation of mechanical and free vibration properties of the pineapple leaf fibre reinforced polyester composites. Constr Build Mater 195:423–431. https://doi.org/10.1016/J.CONBUILDMAT.2018.11.081 6. Faruk O, Bledzki AK, Fink HP, Sain M (2012) Biocomposites reinforced with natural fibers: 2000–2010. Prog Polym Sci 37:1552–1596. https://doi.org/10.1016/J.PROGPOLYM SCI.2012.04.003 7. Asim M, Jawaid M, Abdan K, Ishak MR (2017) The effect of silane treated fibre loading on mechanical properties of pineapple leaf/kenaf fibre filler phenolic composites. J Polym Environ 26(4):1520–1527. https://doi.org/10.1007/S10924-017-1060-Z 8. Najeeb MI, Sultan MTH, Andou Y et al (2020) Characterization of silane treated Malaysian Yankee pineapple AC6 leaf fiber (PALF) towards industrial applications. J Market Res 9:3128– 3139. https://doi.org/10.1016/J.JMRT.2020.01.058 9. Kellems RO, Wayman O, Nguyen AH et al (1979) Post-harvest pineapple plant forage as a potential feedstuff for beef cattle: evaluated by laboratory analyses in vitro and in vivo digestibility and feedlot trials. J Anim Sci 48:1040–1048. https://doi.org/10.2527/JAS1979. 4851040X 10. Chen H (2014) Chemical composition and structure of natural lignocellulose. In: Biotechnology of lignocellulose, pp 25–71. https://doi.org/10.1007/978-94-007-6898-7_2 11. Danladi A., Shu’aib J. (2014) Fabrication and properties of pineapple fibre/high density polyethylene composites. Am J Mater Sci 4:139–143 12. Reddy M, Adaveesh B, Mohan Kumar TS, Nagaral M (2022) Tensile and flexural behaviour of graphite filler particles and pineapple leaf fiber (palf) reinforced polymer composites. Metall Mater Eng 28:141–155. https://doi.org/10.30544/659 13. Arib RMN, Sapuan SM, Ahmad MMHM et al (2006) Mechanical properties of pineapple leaf fibre reinforced polypropylene composites. Mater Des 27:391–396. https://doi.org/10.1016/J. MATDES.2004.11.009 14. Akter M, Jahan E, Hasan M (2018) Mechanical, thermal and morphological properties of pineapple and betel nut husk fiber reinforced hybrid polypropylene composites. IOP Conf Ser: Mater Sci Eng 438:012026. https://doi.org/10.1088/1757-899X/438/1/012026

Natural Fiber of Palm Empty Fruit Bunches (PEFB) Reinforced Epoxy Resin as Polymer Composites Mohamad Mohshein Hashim, Noraini Marsi, Anika Zafiah Mohd Rus, Nur Sahira Marhaini Sharom, and Asmadi Md Said

1 Introduction In recent years, there has been an increasing interest in seeking fiber solutions for effective and inexpensive composites that absorb energy. Among the many potential ways to use natural fibers to form composites of polymers due to their environmentally sustainable and reusable existence [1]. Natural fibers have many advantages including low density, low cost, biodegradability, acceptable specified properties, improved thermal and insulating properties, and low energy in manufacturing. The natural fibers in polymer composites that have been highly investigated are jute, kenaf, cotton, flax, and hemp. These natural fibers are widely used to provide better performances of tensile strength, flexural strength, stiffness, and elongation to break with binder matrix [2]. It is, therefore practicalal to consider using municipal solid waste (MSW) for the production of natural fibers because of its ability to be converted from waste into useful products and energy [3]. MSW consists of organics, paper, plastics, glass, M. M. Hashim · N. Marsi (B) · N. S. M. Sharom Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia, Pagoh Campus, KM 1, Jln Panchor, Edu Hub Pagoh, 84600 Pagoh, Johor, Malaysia e-mail: [email protected] N. Marsi · A. Z. M. Rus Advanced Manufacturing and Material Centre (AMMC), Institute of Integrated Engineering, Universiti Tun Hussein Onn Malaysia, Parit Raja, 86400 Batu Pahat, Johor, Malaysia M. M. Hashim My Flexitank Industries Sdn Bhd, Plot 3 & 4, Jalan PKNK 3, Kawasan Perindustrian LPK Fasa 3, 08000 Sungai Petani, Kedah, Malaysia A. M. Said Angkasa Kowaris Plastic Sdn Bhd, Lot 15796, Block A&B, Jalan Kebun Tambahan, Seksyen 32, 40460 Shah Alam, Selangor, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_14

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metals, and others. Organic waste is made up of food waste, garden waste, wood, peel, or husk [4]. In Malaysia, Palm Empty Fruit Bunches (PEFB) is one of the highest garden waste production. As Malaysia is one of the world’s largest oil palm companies and experiencing robust growth through giant government companies such as the Federal Land Development Authority (FELDA), Federal Land Consolidation and Rehabilitation Authority (FELCRA), Rubber Industry Smallholders Development Authority (RISDA) and private estates such as Sime Darby Plantation, IOI Plantation, Genting Plantation, and others in new plantations and palm oil mills [5]. This abundance of PEFB from the garden is a natural source of fibers and can be used in the polymer composite as potential reinforcement materials [6]. In addition, plastic is one of the MSW components including Polyethylene Terephthalate (PET), High-Density Polyethylene (HDPE), Polyvinyl Chloride (PVC), LowDensity Polyethylene (LDPE), Polypropylene (PP), and Polystyrene (LS) [7]. LDPE is also the largest amount of waste up to 3737 metric tonnes [8]. Thermoplastic polymers are examples of typically used binder matrices which are polypropylene (PP), polyvinyl chloride (PVC); polyethylene (PE); polyurethane (PU), and polystyrene (PS) [9]. Meanwhile, thermoset polymers include phenolics, epoxies, isocyanates, and unsaturated polyesters [10]. In the case of thermoplastic polymers, the recycling and incineration process are the usual elements of the recovery method [11]. However, there is some problem with incineration such as the production of toxic gases and the residues of ash containing lead and cadmium [12]. There are benefits to recycling such as reducing environmental issues and saving both material and energy [13]. These materials, such as another type of waste, can be converted into highdemand bio-based products, particularly in the fields of bio-energy, bio-agriculture, eco-products, and bio-chemicals [14]. The oil palm from Malaysia is the most important one that helped to change the agriculture and economy scenario. Lignocellulosic biomass derived from the oil palm industry includes oil palm trunks (OPT), oil palm fronds (OPF), palm empty fruit bunches (PEFB) and palm pressed fibers (PPF), palm shells, and palm oil mill effluent palm (POME) [15]. However, the presence of such biomass palm waste has created a significant disposal challenge [16]. The core principles of waste management are to reduce and recycle the waste, recover resources and eventually dispose of the waste [17]. These principals refer to agro-industrial wastes such as palm oil residues as municipal solid (MSW) and no longer enable the dumping of residues where there is an economically useful alternative. Researchers need to consider the existing uses and disposal of mill residues to resolve the potential for energy recovery in the palm oil industry to solve the issue [18]. One of the unique features of Malaysian renewable energy sources is that the palm oil mill is energy self-sufficient, using PPF, EFB, and shell as fuel to generate steam for processing in waste-fuel boilers and steam turbines for power generation for the industrial sector [19]. Industrial growth continues with physical materials and sustainability for commodity manufacturing and technical methods requiring a variety of innovative materials that can be extended and which have a long-term market opportunity [20]. Without materials, there will be no food and shelter technology, there might be no work, thus, no economic development [21]. A renewable resource is necessary to

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fulfill the energy requirement. Oil palm waste is a reliable resource due to its green energy, availability, continuity, and capacity for renewable energy solutions [22]. The palm tree consists of about 90% of biomass waste and just 10% oil [23]. In 2020, approximately 90 million tonnes of oil palm fruit were made and 43–45% of this was mill residues in the form of PEFB, shell, and fiber [24]. In addition, the presence of oil palm biomass waste of PEFB in the current scenario produces a severe waste disposal problem and thereby impacts the environmental [25]. To meet the best possible solution for oil palm biomass waste of PEFB, the technical, economical, energy balance and environmental requirements must be balanced. The same issue for plastic waste, LDPE plastic waste from packaging film also poses a low index mechanical recycling that causes numerous environmental problems and is used after discarding for its maintenance [26]. More than one billion LDPE plastic waste has ended up in Malaysian landfills since 2003, according to the State of Malaysia Department of Conservation. LDPE plastic waste does not degrade into landfills and consumes petroleum [27]. Beyond reducing waste and creating a cleaner world, there are practical benefits to researchers making an effort to recycle LDPE plastic waste [28]. The growing production of LDPE plastic waste on a global scale is startling. This exponential increase in plastics production is due to the socalled ‘plastic revolution’ in which chemists are developing new methods to expand the limits of polymers [29]. However, plastic products are starting to be targeted by new environmental legislation. By melting or burning, LDPE plastic waste may be removed, but this results in other issues, such as toxic fumes and a contribution to global warming [30]. LDPE plastic waste incineration would have a detrimental effect on the environment, such as air pollution which emissions into the atmosphere, the generation of polluted wastewater and washes into the air [31]. New alternative approaches to recycling LDPE plastic waste, include blending the mixing of virgin polymer with recycled material [32]. Usage of additives to strengthen formulations, natural fiber polymer reinforcing experiments is suitable to create polymer composites with superior mechanical properties [33]. Sustainable development can also be encouraged by the long-term promotion of bio-products from polymer composite projects with the use of local expertise and the creation of employment [34]. Therefore, the safest way to dispose of the abundantly usable LDPE plastic waste and reduce the amount of incineration, LDPE plastic waste as a filler can be implemented with reinforcement of polymers with natural fiber to produce polymer composite material in the fabrication of deck panel applications [35]. The preparation of polymer composites from a recycled thermoplastic such as LDPE plastic waste reinforced by natural fiber such as PEFB is an interesting alternative that contributes to the preservation of natural resources, the decrease of pollutant waste, production of low-cost materials, a green environment, and sustainable technology [36]. Due to their mechanical and physical properties, PEFB fibers and LDPE plastic waste are ideal for producing the polymer composite as a reinforcing material in the deck panel applications [37]. The study of polymer composites has increased

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because the number of technological advantages does not require high temperatures, long periods, and complex manufacturing processes [38]. It can be transformational behavior without failure to the reinforcement materials at low temperature and produces high durability of polymer composites [39]. The deck panel is highly commonly used for building purposes [40]. A Deck panel is a non-load bearing interior wall mounted on a wall for decorative and division purposes [41]. Deck panel systems encouraged stick-built walls for prefabrication of office wall partitions throughout the fifteenth century [42]. Recently, building markets have shown signs that lightweight deck panel solutions such as drywall, ceiling panel, deck stairs, garden chair, gate paneling, and outdoor decking are used routinely [43]. This research is to utilize PEFB fiber mixed LDPE plastic waste to produce PEFB-LDPE polymer composite as the main raw material for the production of deck panels. The present natural fiber of PEFB fiber in the polymer matrix has potential and advantages in sustainability the use of raw materials from municipal solid waste (MSW). It offers the possibility of improving the physical and mechanical properties and developing sustainable materials used.

2 Literature Review 2.1 Natural Fiber of Palm Oil Waste Palm oil is a commodity that is rising very quickly in global demand and contributes greatly to economic growth. Oil palm, especially in Indonesia and Malaysia, is one of the best-known and most widely cultivated plant families [44]. Increased demand for palm oil in the form of vegetable oils is stimulating the production of oil palm plantations in countries [45]. A lot of oil palm biomass waste has been generated by the oil palm industry in fields and oil palm mills [46]. The mill waste consists of pressed fruit fibers, empty fruit bunch, oil palm shells, and palm oil mill effluent, while the other planting waste consists of oil palm trunks and oil palm fronds during replanting after their economic life spans have been reached [47]. Oil palm waste is a green potential. As a result, the growing growth of the palm oil industry would lead to a rise in effluent from palm oil mills [48]. The oil palm empty fruit bunch (PEFB) of the oil palm as seen in Fig. 1 is a prospective natural fiber to be tested [49]. The PEFB reinforced polymer composite has been studied in recent studies to yield even better features. PEFB is classified as a waste of the palm oil industry produced from the operation of oil extraction mills. In Malaysia especially, there are giant government companies that involve in palm oil plantations such as (FELDA, FELCRA, and RISDA) and private estates [50]. A study by Awalludin et. al. shows the percentage of palm oil plantation ownerships in Fig. 2 [51]. Figure 3 shows the expansion of oil palm plantations cultivation in the Malaysian area. For the palm oil factory, just 10% of the gross palm oil consists of Biomass,

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Fig. 1 The natural fiber of oil palm empty fruit bunches (PEFB) [49]

Fig. 2 Percentage of oil palm plantations ownership in 2014 [51]

while the residual biomass is processed as a waste of almost 90% [52]. This dilemma continues to overwhelm plantation operators with issues with the disposal and raises the expense of running the business [53]. Therefore, such oil palm waste has been recycled in several applications to resolve the problem. Waste from oil palm plantations was generated by plantation routines, pruning, and re-plantation work which produces wastes such as fronds and trunks [54]. The same study also stated that oil palm empty fruit bunches and mesocarb fiber also came from oil palm plantations but it was an abundance of natural fiber waste that had high potential and can be utilized ad reinforcing materials in the polymer composite [55]. Other than oil palm empty fruit bunches, oil palm waste was recycled in many ways. Oil palm fronds and trunks are used by animal breeders as feedstock. In the study conducted by Trisakti, oil palm empty fruit bunch (PEFB) transformed into soil conditioners [56]. The reuse of PEFB as soil conditioners, however, is still not common and there is still enormous unnecessary PEFB waste to be dealt with.

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Fig. 3 Expansion of oil palm plantations cultivation in Malaysia area [52]

3 Municipal Solid Waste The definition of municipal solid waste (MSW) has varied among countries in the world. However in the case of Malaysia, solid waste is classified as any discarded material or other unused surplus or discarded product resulting from the application of any process, any substance that is to be disposed of as lost, worn out, polluted, or otherwise spoiled, or any other material that is to be disposed of by the Authority and does not include intended waste [57]. In 2018, Malaysians spent up to 33,000 metric tons of waste regularly, resulting in the government spending around RM1.2 billion on collecting waste [58]. This condition includes a primary emphasis on the treatment of solid waste and the prevention of detrimental environmental consequences [59]. Municipal solid waste (MSW) comprises toxic contaminants composed of volatile organic compounds (VOCs), polychlorinated biphenyls (PCBs), heavy metals, radioactive materials, and pharmaceuticals extracted from paper, packaging, fruit, plastic, diapers, packaging, and laundry waste that can affect people’s health as shown in Fig. 4 [60]. Therefore, reliable estimates of solid waste generation are very important for proper waste management planning. However, due to the variation in consumption patterns and lifestyle changes, the quantity, and quality of waste change, which requires the monitoring of the quantitative composition of municipal solid waste. MSW with the highest percentage according to Chen et al. was food and organic waste [61]. Usually, the term ‘waste’ conjures up a material image of little meaning or user intent. The term municipal solid waste (MSW) is commonly used to describe rural or urban non-hazardous solid waste that involves regular recycling and transportation to the processing or disposal site [62]. However, solid and industrial waste production is growing at an unprecedented pace. The increasing amount of urban solid waste (MSWs) in landfills is difficult to dispose of and certain persons in their area would

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Fig. 4 MSW composition percentage [61]

not accept MSWs. If present trends continue, the majority of our landfills will be closed shortly [63]. MSW can be found in two types, which is wet waste and dry waste. Examples of wet waste or wet garbage are such as food waste like vegetables, meat, human leftover food, eggshell, and many more [64]. Despite that, dry waste or dry garbage can be seen as paper, tin, cans, wood, bottle, and others [65]. In Table 1, according to Act 672, the Solid Waste and Public Cleansing Management Act show the type of waste and its definition [66]. Government of Malaysia the type of solid waste which also can be called controlled solid waste can be divided into eight categories: commercial solid waste, construction solid waste, household solid waste, industrial solid waste, institutional solid waste, imported solid waste, public solid waste, and solid waste that may be prescribed from time to time [67]. MSW consists of various forms of waste from different areas, such as industrial, commercial centers, institutions, manufacturing, and the city center sector tabulated in Table 2 [68]. Solid waste generation from other sources, such as private, manufacturing, institutional and municipal facilities, should be provided by effective municipal solid waste management. MSW composition makeup ranges greatly from one municipality to another and from one region to another [69].

4 Composite Materials Composite materials consist of two or more distinctly different, spontaneously producing or occurring physical or chemical properties that remain separate and distinct within the finished structure. Because of its many benefits such as low weight, oxidation resistance, high fatigue capability, and quick assembly, composite is an important part of today’s materials [70]. Its characteristics can be engineered for

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Table 1 Type of waste and its definition [66] Types of waste

Description

Commercial solid waste

Any solid waste generated from any commercial activity

Construction solid waste

Any solid waste generated from any construction or demolition activity, including improvement, preparatory, repair, or alteration works

Household solid waste

Any solid waste generated by a household, and of a kind that is ordinarily generated or produced by any premises when occupied as a dwelling house, and includes garden waste

Industrial solid waste

Any solid waste generated from industrial activity

Institutional solid waste

Any solid waste generated by: (a) any premises approved under any written law or by the state authority for use wholly or mainly for religious worship or for charitable purposes (b) any premises occupied by any federal or state government department, any local authority or any statutory body (c) any educational premises (d) any healthcare facilities including hospitals, clinics, and health centers (e) any premises used as public zoos, public museums, public libraries, and orphanages

Imported solid waste

Any solid waste generated in other countries and imported to Malaysia for processing or disposal

Public solid waste

Any solid waste generated by public places under the supervision or control of any local authority

Solid waste which may be prescribed from time to time

Any solid waste generated at a specific time or occasion only

Table 2 MSW source and type of solid waste [68] MSW sources

Types of solid waste

Residential

Food waste, food containers and packer cans, bottles, papers and newspaper, clothes, garden waste, diapers, furniture waste

Commercial Centre (office lot, small shop, restaurant)

Vary types of papers and boxes, food waste, food containers and packer, can, bottles

Institutional (school, university, college, hospital)

Office waste, food waste, garden waste, furniture waste

Industry (factory)

Office waste, cafeteria waste, processing waste

City Centre (drainage and road)

Vary types of garden waste, construction waste, public waste

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Fig. 5 Classification of composites materials [75]

specialized applications for many things. Two mixed components are insoluble in each other, known as the reinforcement process and the embedded matrix [71]. In a discontinuous form that is generally tougher than the matrix, the reinforcement phase is embedded in the matrix, while the matrix phase has a continuous activity that is usually more ductile and less hardened [72]. In terms of lightweight, solid and versatile molding into complicated shapes, new composite materials have the greatest advantages [73]. By finding an appropriate mix of matrix and reinforcement materials, it is possible to create a new material that will fulfill the particular design specifications. Composite materials, similar to aluminum or steel, are lightweight but have high strength. The materials are resistant to degradation due to temperature and chemical reactions that may affect other materials [74]. Polymer composites (PC), metal composites (MC), and ceramic composites (MC) are the three primary classifications of composite materials in Fig. 5 [75]. Polymer composite materials include composite materials based on thermoset resin and composite materials based on thermoplastic resin, as well as single-component polymer composite materials and polymer composite materials [76]. In general, metal composites have a comparatively high individual mass and metal composites are not in high demand because of their high density [77]. In the aeronautical and astronautical industries, ceramic composites are widely used as thermal structural materials [78].

5 Polymer Composites The polymer composites material found are made of a fiber-reinforced polymer matrix. In a wide variety of uses, particularly in the aerospace and automotive industries, fiber-reinforced polymer technologies have been used successfully for many years [79]. The mechanical and physical properties of the Polymer Composite Matrix (PCM) are determined by their constituent properties and by the configuration of the microstructure [80]. These days, researchers have focused primarily on the resin solution of polymer composite materials. Polyester, epoxy resin, polyimide, polypropylene, vinyl ester, and others were the most common resin solutions that were used [81].

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These resins are called non-degradable and can remain in the anaerobic atmosphere of landfills for decades or even centuries without any modification [82]. Because of the fiber properties and benefits in terms of comparatively lightweight, low cost, less damage to processing equipment, strong mechanical properties, and excess in the landfills that caused environmental problems, the reinforcing materials typically used fibers [83]. Polyester, epoxy resin, polyimide, polypropylene, vinyl ester, and others were the most common resin solutions that were used. Due to its low cost and easy production methods, polymer composites (PC) have become very successful [84]. Because of the fiber properties and benefits in terms of comparatively lightweight, low cost, less damage to processing equipment, strong mechanical properties, and excess in the landfills that caused environmental problems, the reinforcing materials typically used fibers [85]. For their excellent properties such as enhancing mechanical performance in terms of tensile strength, flexural strength, impact strength, and sound absorption, the studies of polymer composites strengthening solid waste have drawn due consideration from academics and industrialists [86]. The tensile strength of unidirectional glass/epoxy composite laminates with various percentages of glass fiber was investigated and suggested that the maximum composite strength was obtained by the highest percentage of glass fiber in glass/epoxy composites [87]. A researcher, Nieto et al. was examined the mechanical stress activity of composite materials composed of a polymer matrix of epoxy resin and polyester resin and reinforced with nylon fibers and fiberglass, arguing that since the nylon fiber is hydrophilic, the improved tensile strength was attributed to greater water absorption with the higher proportion of resin in the composite material [88]. Dong et al., (have contrasted the flexural resilience of the epoxy-matrix hybrid composite reinforced carbon fiber and glass fiber with the glass fiber reinforced epoxy matrix composite and the epoxy matrix composite reinforced carbon fiber. Found that the hybrid composite flexural performance is considerably higher compared to the other two components [89]. Composite material is a material made out of at least two particular stages. The first stage is the matrix phase and the second stage is the reinforcement phase which has mass properties altogether extraordinary structure those of any of the constituents [90]. The first stage, having a continuous character, is called matrix. Matrix is usually more ductile and less hard phase. It holds the dispersed phase and shares a load with it. The first stage would be made with matrix constituents. According to Sangeeta et al., the matrix of a composite can be polymer, metal, or ceramic [91]. Based on Mohamad et al., the second stage applies to the fortification shape, which not just gives a high solidarity to-weight proportion, yet additionally shows amazing properties, for example, high sturdiness, unbending nature, flexural strength, and consumption opposition [92]. This secondary phase is called the dispersed phase. Karim et al. stated that reinforced polymer composite materials, which are fiberreinforced composites, particulate composites, laminar composites, filler composites, and flake composites, have five classifications as shown in Fig. 6 [93]. The efficiency of the composites of natural fibers depends directly on the counting, weight, shape, arrangement, and interfacial adhesion of the fibers with the matrix [94]. Natural fiber reinforcement may be divided by length, dimension, and orientation.

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Fig. 6 Type of polymer composites materials [93]

This can be either in fiber or particle shape. Depending on the length to diameter, the fiber itself is defined as continuous or discontinuous such as chopped [95]. Cellulose in the 60–80% range, hemicellulose in the 5–20% range, lignin, and humidity in the 20% concentration range are the main components of natural fibers [96]. The fibers used may be continuous or discontinuous and may be designed to lie in the same direction or randomly directed. The compression test typically decides the sandwich material’s conduct under pressure loads and ductile fracture limits [97]. As shown in Fig. 7, the sandwich structure is the most widely used composite material [98]. Figure 8 shows the arrangement of the lamina with their reinforcement by laminating it in at least two different directions [99].

Fig. 7 Laminar composite for sandwich structure [98]

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Fig. 8 Stack of lamina for laminar composites [99]

6 Methods for Fabrication Polymer Composite by Hand Lay-Up Techniques It is the most basic fabrication method for thermoset composites which typically consists of laying dry fabric layers, or “plies,” or prepreg plies, by hand onto a tool to form a laminate stack in Fig. 9 [100]. After the layup is complete, the resin is added to the dry layers. Dry fibers are manually placed in the mold in the form of spun, knitted, stitched, or bonded materials, and a brush is used to apply the resin matrix to the reinforcing material [101]. To treat conditions that require the use of an autoclave, many high-performance thermoset parts involve heat and high consolidation pressure. To ensure improved contact between the reinforcement and the matrix, hand rollers are used to roll the wet composite and the laminates are left to cure under standard atmospheric conditions [102].

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Fig. 9 Hand lay-up methods for polymer composite fabrication [100]

7 Previous Study Natural Fiber into Polymer Composites Because of its many advantages such as uncomplicated manufacturing, low density, actual power, comparatively high stiffness, and the most important is the biodegradation of nature, the PEFB can be considered potential to be highlighted in polymer composite [103]. Several experiments and attempts by Rohadi. et al., conducted PEFB for value-added products such as bio-adsorbent, bio-oil, pulp, activated carbon, electrical, bio-energy, bio-resource, and chemistry field. Patra. et al. have researched the flexural and tensile properties of a polypropylene (PP) composite reinforced by PEFB fiber and fiberglass agents [104]. In the PP matrix, the integration of PEFB fiber has resulted in a decrease in flexural and tensile strength and as a result, the flexural and tensile modulus was found to improve with an increasing level of overall fiber content loading [105]. After some improvements were made to lower the interfacial strain between the matrix and the fiber filler of the EFB, Hee-Soo et. al., was stated that the maleic anhydride polypropylene-g-polypropylene (MAPP) was chosen to provide compatibilizer or treating the surface or both, improve impact resistance and increased degradation temperature [106]. Hashim, et al., studied polyurethane-based PEFB. PEFB fibers were used in the form of mats where they were treated with Diisocyanate hexamethylene (HMDI) and toluene diisocyanate (TDI). The study of PU-EFB composite was found to have appropriate properties, which were thought to be mainly affected by the form of bond made. It concluded the optimum result up to 23 MPa, 1.3 GPa, 4.4%, 4.5 J, 75 MPa, 1.7 GPa, 4.8 J, 19 J/m2 respectively, for tensile strength, tensile modulus, split elongation, tensile strength, flexural strength, flexural modulus, flexural strength and impact strength [107]. Investigation of the mechanical properties of PEFB, Fodzi, et al. produce matrixes of EFB fibers and its cellulose with polypropylene (PP). In terms of tensile strength, impact strength, and flexural modulus, PP-EFB and PP cellulose behaved differently. The result found were, in all directions where the maximum tensile strength is 35 MPa, the impact strength is 38 J/m, and flexural modulus is 4000 MPa, PP-EFB is 20 MPa, 32 J/m, and 2700 MPa respectively, PP-cellulose performed higher [108].

226 Table 3 The various composites fiber impact test result [109]

M. M. Hashim et al. Composite materials

Impact strength results (J/m)

Pure epoxy

30.4

Pure PEFB

92.7

PEFB/Jute/PEFB

66.7

Jute/PEFB/Jute

57.0

Pure Jute

32.0

Another study has been done by the previous researcher to explore PEFB as a hybrid composite for widening its potential in Table 3. Faizi et al., prepared a test for a different layer of the mat: EFB-jute-EFB; jute-EFB-jute, and in the bending test, the jute-EFB-jute had the highest flexural strength and modulus efficiency at 49 MPa and 3.07 GPa respectively. As OPEFP for energy absorption, the impact strength of PEFB needs to be improved [109]. Yeoh, et al. revealed its potential by using isocyanate treatment, the impact strength of PEFB has increased from 8 to 20 J/m2 [110]. By deriving PEFB cellulose, Khalid, et al. have increased impact strength from 32 to 38 J/m [111]. After several years, Akonda, et al. found the best material which is maleic anhydride polypropylene-polypropylene (MAPP), and characterized PEFB with MAPP to get 34,000 J/m2 for the content of 8% of the MAPP [112]. In Table 3, different composite materials have been compared to know the energy absorption among the material. The impact tests were performed on a different sequence of fiber mate sandwich arrangements. With 92.7 J/m of energy absorption power, the pure PEFB composite shows a remarkable performance which means PEFB has the stronger impact strength. while pure epoxy shows the weakest impact strength with 30.4 J/m [113]. One of the main problems experienced by the Department of Environment Malaysia is determining the best way to dispose of municipal solid waste (MSW), particularly the garden waste of PEFB and plastic waste of LDPE [114]. In 2020, more than 20 million tonnes of PEFB waste production, placed as the world’s secondlargest producer in 2019. PEFB is considered the cheapest natural fiber with suitable properties and exists abundantly in Malaysia. It has excellent potential as an alternative primary raw material to substitute synthetic fibers [115]. Meanwhile, LDPE plastic’s worldwide annual production reached 300 million tonnes, yet worldwide plastic recycling contributed to only 10% of this production. The plastic recycling and incineration process are the usual aspects of recovery methods in thermoplastic polymers [116]. The incineration presents some problems like toxic gases and residue ash, which contains lead and cadmium. Recycling offers advantages such as reduction of environmental issues and saving both material and energy. It has to benefit LDPE plastic waste to implement into recycled materials through grinding or shredding to reinforce polymers with natural fiber to produce composite material such as deck panels [117]. Deck panels from composite materials are ideal candidates to replace conventional materials such as wood and concrete have their weaknesses such as low durability, and

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the loss of density only slightly influences the heavyweight and mechanical performance of the compression and bending strength [118]. The need for high-quality locally made material for the deck panel is in higher demand due to the out-of-reach costly imported deck panels [119]. Therefore, a new bio-product of composite deck panel made from the PEFB fiber and LDPE plastic waste will be determined in this study. Many researchers worldwide have studied polymer composite as reinforced materials for waste including plastic, glass, wood, and paper as reinforced materials [120]. The proposed materials in this study are PEFB fibers and LDPE plastic waste. However, the study on the utilization of the PEFB fibers and LDPE plastic waste in the composite materials is limited. PEFB fibers are the main natural fibers in the composite materials that possess better mechanical properties such as high tensile strength, high flexural strength, superior impact property, and soundproof properties [121]. Using polymerization formulation, polyurethane resin will be converted from liquid to solid-state in a cross-linked molecular structure to form polymer composites whereas previously, synthetic resins contained celluloid, melamine, and Bakelite [122]. These modern polymer composite materials will be expected to improve performance than other synthetic composite materials. Nevertheless, LDPE plastic waste alone could not have enough strength and rigidity for structural applications. To increase the system’s strength and rigidity, it is, therefore, necessary to provide further reinforcement [123]. Hence, the proposed materials in this study, PEFB fiber, and LDPE plastic waste help improve the PEFB-LDPE polymer composites.

8 Methodology The first step in the fabrication process of composite partition panels was to prepare the raw materials. Palm Empty Fruit Bunches (PEFB) fibers were collected from Kilang Kelapa Sawit Bukit Pasir Sdn. Bhd. as waste fiber. The type of epoxy resin used was the DER 324 Liquid Epoxy Resin from DOW Company and the fast hardener type as hardener was the Jointmine 905-3s from SUKA Company, Shah Alam. The cleaning process of Palm Empty Fruit Bunches (PEFB) fibers was performed at Kilang Kelapa Sawit Bukit Pasir Sdn. Bhd., a company located in Bukir Pasir, Muar. The PEFB fiber used in this study has been collected from the landfill. The PEFB fiber was collected and transferred to the recycling center at the company. Seven samples of composite panels were prepared with different proportions of Palm Empty Fruit Bunches (PEFB) fiber-reinforced epoxy resin was tabulated in Table 4. PEFB ratio was involved 0–0.6 based on the preliminary test performed, the composition ratios were chosen and limited to the ratio of 0.6.

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Table 4 Composition of different ratios of PEFB fiber-reinforced epoxy resin Samples

PEFB ratio

Epoxy resin ratio

Hardener ratio

A

0.0

3

1

B

0.1

3

1

C

0.2

3

1

D

0.3

3

1

E

0.4

3

1

F

0.5

3

1

G

0.6

3

1

9 Results and Discussions 9.1 Density and Porosity Analysis PEFB reinforced epoxy resin composites were subjected to density and porosity tests. As the porosity of the samples increases, the density of the samples dropped. According to Liu, et al., the increased density of composites implies improved epoxy interfacial bonding and the reduction of micro-voids. This could be due to the low interfacial bonding between the PEFB and epoxy-matrix composition [124]. Figure 10 depicts the connection between density and porosity for PEFB reinforced epoxy resin composites of various ratios of PEFB fibers.

Fig. 10 Relationship between density and porosity for PEFB reinforced epoxy resin composites

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The density of the PEFB reinforced epoxy resin composite decreases with increasing filler content, as expected, due to the light density of the filler in comparison to the epoxy resin, whereas the porosity increases with increasing filler content, possibly due to the low interfacial bonding between the fillers and epoxy resin composition. According to Marsi, et al., the existence of improved interfacial bonding with epoxy, as well as the reduction of micro-voids by raising the composite’s density [125]. In Fig. 10 show the result density and porosity for PEFB reinforced epoxy resin (PEFB/epoxy) with the lower ratio, 0.1 resulted in a greater density of 1.1239 g/cm3 , followed by ratios of 0.2 PEFB/epoxy with 1.0914 g/cm3 , ratio 0.3 PEFB/epoxy with 1.0677 g/cm3 , ratio 0.4 PEFB/epoxy with 1.0591 g/cm3 . The trend increased at ratio 0.5 PEFB/epoxy with 1.0690 g/cm3 and ratio 0.6 PEFB/epoxy with 1.0794 g/cm3 . The ratio of 0.6 PEFB/epoxy had the greatest apparent porosity with 15.8%, followed by ratios of 0.5 PEFB/epoxy with 13.7%, ratio 0.4 PEFB/epoxy with 13.1%, ratio of 0.3 PEFB/epoxy with 12.8%, 0.2 PEFB/epoxy with 11.7%, and finally ratio of 0.1 PEFB/epoxy with 8.6%. Due to an insufficient amount of epoxy resin or a greater viscosity, KamranPirzaman, et al. was stated that the epoxy resin may not be capable of filling all the gaps formed between the filler particles with high filler content, resulting in poor flowability with a high filler content [126]. According to Lo, et al. study, bubbles formed from volatile by-products generated during the curing process of a high-viscosity polymer resin, coupled with tightly wrapped resin-wetting fibers, result in the materials system retaining air. The saturation condition of the PEFB with the epoxy resins and the formation of bonds between them increased the apparent porosity of the PEFB/epoxy composite materials, resulting in the undesired development of voids if epoxy resins were not present [127].

9.2 Scanning Electron Microscope (SEM) Analysis For the PEFB reinforced epoxy resin composite composites, SEM image analysis, and EDX data have been seen and analyzed. Figure 11 shows SEM pictures of pure epoxy resin and PEFB reinforced epoxy resin composite shows crack surfaces. SEM images can detect the cross-section morphology and microstructure of the composites, indicating the decisive causes of rupture during mechanical testing. The pure epoxy resin composites without any fiber, which displayed brittleness with smooth and river lines appearing on the broken surface of the epoxy resins, reflected the PEFB reinforced epoxy resin without PEFB. Tensile stress building at the fibermatrix interface caused fiber-matrix interface failure, resulting in adhesive fracture. Due to the adhesion between the matrix and the fibers, deformation in the fiber matrix is restricted, but when the matrix deforms, local stress develops in the matrix, resulting in interfacial fissures. Younis, et al., investigated in the direction of crack 80 propagation, little and sharp markings were opened [128]. The fillers were properly dispersed throughout the epoxy resin according to all PEFB reinforced epoxy resin composite ratios. Based

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A

Smooth Exterior

B Broken Fibres

Crack Pull-out Fibres Wavy Exterior

C

D

Pull-out Fibres Pull-out Fibres

Broken Fibres

Broken Fibres

F

E

Pull-out Fibres

Broken Fibres

Broken Fibres Pull-out Fibres

G Pull-out Fibres

Broken Fibres

Fig. 11 SEM image of fractured sample: ratio a control sample (0.0); b 0.1 PEFB; c 0.2 PEFB; d 0.3 PEFB; e 0.4 PEFB; f 0.5 PEFB; g 0.6 PEFB reinforced epoxy resin

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Fig. 12 Tensile strength at different ratios of PEFB/epoxy

on Fig. 11e–g shows many pulled-out fibers in SEM images for PEFB reinforced epoxy resin composite ratios of 0.4, 0.5, and 0.6, indicating poor and weak interfacial bonding between the filler and the epoxy matrix. As demonstrated in Fig. 12, the presence of cavities and pull-out fibers in the matrix weakens composite bonding. An SEM picture of 0.6 PEFB reinforced epoxy resin composite ratios revealed a cluster of fibers and patches with limited filler dispersion inside the epoxy matrix. This is supported by a statement from Shankuntala, et al. was investigated the absence of an adequate epoxy matrix to allow efficient wettability of the filler leading to the buildup of PEFB waste filler and micro spaces within the matrix. PEFB reinforced epoxy resin ratio of 0.6 mechanical properties had been reduced because of poor dispersion of incompatible PEFB waste filler and its limited adhesion [129]. The localized group of fibers and patches, as seen in the SEM image of ratio 0.4 to 0.6 PEFB reinforced epoxy resin composite in Fig. 11 shows poor filler dispersion within the composite. The number of broken fibers showed improved adhesion between fillers and epoxy resin in SEM images with PEFB reinforced epoxy resin composite ratios of 0.3 as illustrated in Fig. 11d. When the covalent connections between the fiber and the matrix are disrupted, the interface failure mode for fiber-matrix occurs, impacting the load delivered to the fiber. In a study by Zhang et al., the fractures behavior of the composites, as defined by the tensile stress level, was addressed through an interface zone, the contact zone between fiber and resin, according to the micrograph analysis [130]. Because researchers focused more on the surface image of the samples, SEM investigations on composite cross-section surfaces before and after failure were not extensively published. Despite that, if an adhesive link is utilized to connect two surfaces, the cohesive fracture is the optimal failure mode, and adequate adhesion between the matrix and fibers is critical for composite materials employed as a load carrier element.

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9.3 Tensile Strength Analysis The PEFB/epoxy resin composites’ tensile strength is plotted in Fig. 12. above. According to the graph, the PEFB/epoxy resin ratio of 0.3 has the maximum tensile power with 18.18 MPa, led by ratios 0.4 with 13.79 MPa, ratio 0.5 with 9.62 MPa, ratio 0.6 with 9.54 MPa, ratio 0.2 with 7.81 MPa, and ratio 0.1 with 5.09 MPa. Jong, et al. stated that for poorly bonded samples, stress transfer at the fiber interface is inefficient, and the discontinuity in the form of de-bonding is caused by the epoxy matrix’s lack of adhesion to the fiber [131]. The presence of PEFB waste as fillers in the epoxy mixture increased the tensile strength of the composites, as seen in Fig. 12. Since the matrix epoxy-filler matrix was robust in terms of interfacial bonding, viscosity, and fiber dispersing in the epoxy matrix, the tensile strength obtained for the composite sample at PEFB/epoxy resin ratio of 0.3 was greater than that of other ratios, as anticipated. If the tension increases, the epoxy matrix expands, the filler separates, and the opening in the matrix is pushed out until it breaks. Stress–strain behavior for each PEFB/epoxy resin sample can be seen in Fig. 13. Four linearities and four curvatures were observed early in the deformation process. The epoxy matrix expands as the stress increases, separating the filler and pulling the opening out of the matrix until it breaks. According to Nasir, et al., the polymer composite’s weak primary cell wall crumbles, causing cell decohesion and mechanical failure of the polymers. The highest strain was 58.0% in the 0.5 PEFB/epoxy ratio, this could happen because of the polymer composite matrix’s strong interfacial cohesion bonding [132]. The second highest strain was a PEFB/epoxy ratio of 0.6 with 44.0%. It is followed by 0.4 PEFB/epoxy with 11.0%, PEFB/epoxy 0.2 with 6.52%, PEFB/epoxy 0.1 with 6.28%. 0.3 PEFB/epoxy is the last because it has less strain percentage which is just 3.28%. Because of the strong adhesive force between the fibers and the polymer matrix, each curve shows maximum stress, which is assumed to be the material’s tensile

Fig. 13 Stress–strain for the differratiosatio of PEFB/epoxy

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strength. By bridging the fiber and the matrix, uniform dispersion of PEFB waste filler creates a mechanical interlocking process. The increase in load-bearing strength of the composite during tensile loading is influenced by this mechanism. Zainal Abidin, et al. stated that energy absorption will increase and improved the strength of the composite’s material. When loaded, the matrix begins to crack and becomes the tertiary composite system’s lowest element. The PEFB filler then uses the bridging effect of the mechanical interlocking system to move the load from the matrix to the high modulus [133].

9.4 Impact Strength Test Analysis Impact energy can be measured when the hammer impacts the PEFB/epoxy resin specimen. Then the PEFB/epoxy specimen will absorb the energy until the specimen is yielded. As a result, some of the samples will be taken out of the matrix when the hammer strikes it, but they will not break; instead, they will bend. When the hammer impacted the specimen, plastic deformation will have occurred at the notch of the sample. The effect of energy increased as PEFB/epoxy specimen ratio in the composite increased as seen in Fig. 14. A ratio of 0.3 PEFB/epoxy achieved the highest impact energy of 159.89 J/m. followed by 0.4 with 152.94 J/m, 0.5 with 80.50 J/m, the ratio of 0.2 with 80.27 J/m, a ratio of 0.6 with 41.37 J/m, and the lowest impact energy of 30.66 J/m was obtained by PEFB/epoxy ratio of 0.1. Bezimyanniy et al. studied the reinforced polyester matrix composites’ energy absorption potential has improved noticeably and the addition of polymers to the matrix has increased the composite’s effect hardness dramatically [134]. The decohesion of the fiber/matrix low shear stress interface and tensile rupture of the microfibrils, which results in high energy absorbed due to longitudinal proliferation of cracks and multiple fractured areas, could explain the exponential rise. Figure 15 depicts the connection between absorbed energy and impact strength for various PEFB/epoxy ratios. The highest impact strength was achieved by a PEFB/epoxy ratio of 0.3 with 10.10 kJ/m2 and followed by 0.4 with 5.36 kJ/m2 . PEFB/epoxy 0.5 is similar to 0.4 but it is less than 0.4 with 5.35 kJ/m2 . PEFB/epoxy ratio of 0.6 has 4.4 kJ/m2 . 2.76 kJ/m2 is the result for 0.2 PEFB/epoxy resin. The second-lowest impact strength with 2.04 kJ/m2 is for a PEFB/epoxy resin ratio of 0.2. Controlled samples are the lowest with a 0.98 kJ/m2 impact strength result. The result differs was due to a change in fracture toughness as filler loading was increased. The micro void formed surrounding the filler might induce cracking, compromising the hardening of the material if the filler mixture ratio is low. According to Marsi et al. by mixing PEFB as a fiber, it will have the stronger impact strength, while pure epoxy shows the weakest impact strength. The use of PEFB as a filler in epoxy resin composites does not compromise the material’s characteristics and improves the production process [135]. It is clearly shown that the energy absorbed was continuously increasing with the PEFB/epoxy ratio in epoxy

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Fig. 14 Energy impact against different ratio of PEFB/epoxy resin

Fig. 15 Relationship between energy absorbed and impact strength for the different ratios of PEFB/epoxy resin

resin up to 0.3 ratios. PEFB/epoxy resin 0.4 ratios start to decrease the energy absorption. The addition of PEFB/epoxy resin reduced the impact energy received by the sample.

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10 Conclusion In conclusion, deck panels from composite materials are ideal candidates to replace conventional materials such as wood and concrete have their weaknesses such as low durability, and the loss of density only slightly influences the heavyweight and mechanical performance of the compression and bending strength. The need for high-quality locally made material for the deck panel is in higher demand due to the out-of-reach costly imported deck panels. Therefore, a new bio-product of composite deck panel made from the PEFB/epoxy resin was fabricated in this study. PEFB fibers are the main natural fibers in composite materials that possess better mechanical properties such as high tensile strength, high flexural strength, superior impact property, and soundproof properties. Using polymerization formulation, polyurethane resin will be converted from liquid to solid-state in a cross-linked molecular structure to form polymer composites whereas previously, synthetic resins contained celluloid, melamine, and Bakelite. These modern polymer composite materials will be expected to improve performance than other synthetic composite materials. Nevertheless, LDPE plastic waste alone could not have enough strength and rigidity for structural applications. To increase the system’s strength and rigidity, it is, therefore, necessary to provide further reinforcement. Hence, the use of PEFB fiber help improves the PEFB/epoxy composites. The PEFB/epoxy resin composites produce high mechanical properties and are suited for use in decking panels preparation. Because the mechanical performance of PEFB/epoxy resin composites has been proven by the tensile strength, flexural strength, impact analysis, compression strength, and sound absorption test. The composition ratio of 0.3 PEFB attained the higher ratio at 18.18 MPa with the impact strength at 159.89 J/m and the energy absorb is 4.40%. Flexural strength for the composition of 0.3 PEFB withstood the greatest among other ratios at 44.92 mm and produce maximum deformation value for ductile mode at 26.202 MPa. It is similar to compressive strength for a composition ratio of 0.3 PEFB at 12.59 MPa. In terms of mechanical properties, PEFB with a composition ratio of 0.3 PEFB is good mechanical properties by comparing to other polymer composites including commercial polymer composites such as kenaf fiber, rise husk fiber, and other natural fiber. The use of PEFB reinforced polymer composite in the fabrication deck panels was suitable to replace the natural resource of Kenaf Bast and Kenaf Core. The use of PEFB as a recyclable waste is an environmentally responsible way to create prefabrication technology by decreasing garbage and environmental damage. Other building applications for PEFB composite include furniture, decorative floor, and ornamental walls.

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The Development of Temporary Bone Scaffolds from High Density Polyethylene (HDPE) and Calcium Carbonate (CaCO3 ) for Biomedical Application N. Zulkefli, M. D. Ahmad, S. Mahzan, and E. M. Yusup

1 Introduction This engineering field is taking advantages of the use of porous 3D scaffolds to provide an appropriate situation for tissue and organ regenerations including upgrading current materials involved in the field for future use. Scaffolds act as a template for tissue formation and are seeded with cells including growth factors. These cell-seeded scaffolds are either cultured in vitro to synthesize tissues which can then be implanted into an injured site, or are implanted directly into the injured site, using the body’s own systems, where regeneration of tissues or organs is induced [1, 2]. Many studies have used approaches such as carbonation or solution to produce inorganic calcium carbonate raw material over the past few years [3, 4]. However, scientists and researchers have found new ways of employing nature-based materials such as mineral products extracted from calcium carbonate. The new trend is highly preferable in terms of environmental preservation and due to its nature, cockle shells can provide raw material at reasonable low cost besides having good purity of mineral components naturally [5, 6]. Calcium Carbonate (CaCO3 ) is found naturally in our environment such as seashells, rocks and eggshells. In a related research, CaCO3 was extracted from cockle shells and known for its potential in multiple tissue engineering applications [7, 8]. Cockle shells are commonly found in Malaysia as waste products of food and can also be easily found alongside beaches. The increasing demands of natural materials based on CaCO3 can easily be fulfilled by using cockle shells as the main source due to their low cost and availability [9, 10]. Cockle shells consist of about N. Zulkefli · M. D. Ahmad · S. Mahzan · E. M. Yusup (B) Department of Mechanical Engineering, Faculty of Mechanical and Manufacturing Engineering, University Tun Hussein Onn Malaysia, 86400 Parit.Raja, Batu Pahat, Malaysia e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. H. Ariffin et al. (eds.), Structural Integrity and Monitoring for Composite Materials, Composites Science and Technology, https://doi.org/10.1007/978-981-19-6282-0_15

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96% of CaCO3 whilst other components include organic substances and oxides like Silicon Dioxide (SiO2 ), Magnesium Oxide (MgO) and Sulfur Dioxide (SO3 ) [9, 11]. Research in making biodegradable materials is clinically and experimentally studied to design scaffolds with characteristics. The combination of biodegradable polymers and bioactive inorganic materials are being widely used. In addition, the rate of degradation and the by-products of biodegradable materials are also critical in the role of bone regeneration. The aim of this study is to produce and assess mechanical properties of CaCO3 nanoparticles and HDPE as a potential bone matrix for tissue engineering and strengthening material.

1.1 Problem Statement Allograft and autograft are the most common bone graft treatments in tissue engineering field. Although these treatments are widely used, they are bound to limitation to the patients such as pain, infection, scarring, blood loss, and donor-site morbidity [12]. Thus, the biodegradable and biological materials spark interest in scientists to develop new materials that is safe to use besides highly biocompatible and responsive to human physiological needs [13]. The natural sources of biomaterials have been limited to porcine skin, bovine bones, human bones and corals. Cockle shells are commonly found in Malaysia as waste products of food and can also be easily found alongside beaches [9, 1]. From the observations at the cockle landing sites, cockle shells have been discarded or abandoned in a huge dump. Reusing wasted cockle shells reduces environmental degradation and pollution because dumped cockle shells take a very long time to decay and it is said to have mineral composition similar to corals which means there is a possibility of using cockle shells as an alternative biomaterial for bone substitute in managing bone defects [10]. Polymorphs contained in calcium carbonate are an appropriate biomaterial since it can replace bone tissues. Mixing the organic and inorganic materials together can help upgrade the current materials used in biomaterials for bone tissue engineering to recreate a new reinforced material that is not only affordable but safe for medical usage without harming the user for a long period of time.

2 Methodology 2.1 Cockle Shells CaCO3 Powder Preparation The preparation process started by collecting wasted cockle shells from a seafood restaurant. Before the crushing and grinding of cockle shells can be done, the collected shells must first be cleaned up and left to dry in the open air to assure

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that it did not adhere to the sharp edge of the granulating machine as it could be difficult to wash after being utilized. The pieces of the crushed cockle shells then needed to experience similar procedure several times to obtain the smallest size. The powder of the cockle shells was sifted once with the extent of 200 μm, experiencing the procedure known as ball mills. The estimated time for powder delivered by milling process was less than 100 min. After completion, the CaCO3 powder was sieved with the sponge of the strainer of 100 μm to get a uniform size powder.

2.2 Sample Preparation Mixing process was required to blend CaCO3 uniformly which was synthesized from cockle shells, altogether with high density polyethylene (HDPE) as natural polymer. The final product was stronger composite with more tolerance in flexibility compared to metal material. The mixture from two different materials, which are CaCO3 and HDPE pallets, were mixed using brabender mixing machine at the temperature of 170 °C to make the samples. Nine samples for three different ratios were prepared using the following combinations: ratio 1: CaCO3 10%, HDPE 90%, ratio 2: CaCO3 20%, HDPE 80%, and ratio 3: CaCO3 30%, HDPE 70%. The weight for each material was calculated using brabender machine weight calculation as in Eq. (1): m = V × yc × k

(1)

where m is sample weight, V is mixer chamber volume (55 cm3 ), yc is composite density and k is constant (0.60). Brabender mixing machine was heated to 170 °C while CaCO3 powder and HDPE pallets were weighted according to calculated weight for certain ratios. As the HDPE pallets were melted, the powder was put inside the mixture little by little and left to fully mix for 10 min before repeating the process for different ratio.

2.3 Crushing Process The samples were crushed using the crushing machine to produce smaller size to be used for injection molding. Figure 1 shows the sample before and after crushing in the crushing machine.

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Fig. 1 Sample a before and sample b after crushing process

Table 1 Ratio of samples Sample

CaCO3 (%)

HDPE (%)

No. of sample Flexural test

Impact test

Tensile Test

S1

10

90

3

3

3

S2

20

80

3

3

3

S3

30

70

3

3

3

2.4 Injection Molding All samples for mechanical testing were generated through the process of injection molding using the Nissei NP7 Real Mini machine. Each mechanical testing has different sample shape. According to standard ASTM D638 for tensile test, the sample shape used was Narrow-waisted Dumbbell. The sample shape for flexural test was based on ASTM D790 while sample for impact test was based on ISO 179. Table 1 shows the ratio and how many samples for each mechanical testing will be made.

2.5 Mechanical Testing In this research, flexural, tensile and impact tests were the chosen testing method to obtain the mechanical properties of the composite. The results obtained later should be able to determine whether the composite material is suitable to be used in tissue engineering as a temporary bone implant.

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Flexural Test

Flexural test or three-point bending test was used to determine the bending properties of the material by using Universal Testing Machine (UTM) with 10 kN load cells. The specimen underwent injection molding procedures. All details such as the specimen size and testing procedure are referred to ISO 178-93. The specimen dimension was 80 mm in length, 10 mm in width and 4 mm in thickness.

2.5.2

Impact Test

The Charpy impact test was performed to measure the energy capacity absorbed by the material when subjected to a sudden load [14]. The impact test was important to determine the toughness of the material by measuring the amount of energy absorbed before fracture or fail. The reading of the experiment will be taken in unit Joule. The specimen dimension was 80 mm in length, 10 mm in width and 4 mm thickness and 2 mm notch at the middle. This research used Charpy impact test equipment.

2.5.3

Tensile Test

Tensile tests were carried out to measure the force required to break a plastic sample specimen and to determine to what extend the specimen stretches and elongate to the specific breaking point [15]. Using Universal testing machine (5 kN load cells) with standard ASTM D638 for tensile test, the test will provide data for tensile strength, stress, tensile strain and tensile modulus. The sample shape used was Narrow-waisted Dumbbell.

2.6 Material Analysis 2.6.1

Scanning Electron Microscopy (SEM) Analysis

Examination of prepared samples and CaCO3 powder was done by Scanning Electron Microscopy (JEOL JSM 6400 SEM ATTACHED WITH EDX, Germany) [16]. Tensile and impact test samples were coated in platinum coating prior to studies on electron conductivity, microstructural characterization and sample structure at breaking point for further study. Few milligrams of cockle shell CaCO3 powders were affixed to a stub with carbon paint placed on the sample holder. For solid samples, they were stuck to a metal bar using carbon tape before tested. The sample holder was mounted on a rotatable disc inside the machine and all samples were prepared for both SEM and EDX analyses. The surface morphology of the sample was observed on SEM operated under low vacuum at an accelerating voltage of 15 kV.

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Energy Dispersive X-ray (EDX) Analysis

The same sample was analyzed using EDX to investigate the elemental constituents after the spectrum was determined.

2.6.3

Fourier Transform Infrared (FTIR) Analysis

The FTIR analysis method used infrared light to scan test samples and observe chemical properties. The chemical functionality of the samples were analyzed using the spectroscopic method utilizing a Fourier Transform Infrared (FTIR). Spectrophotometer (Perkin Elmer) was used over the range of 400 cm−1 to 4000 cm−1 with CaCO3 powder, HDPE pallets, sample 1, sample 2 and sample 3, respectively.

3 Results and Discussion 3.1 Flexural Test Table 2 shows the highest maximum force applied to the sample which is 35.83 N for S3 with the ratio of 70% HDPE and 30% CaCO3 . It was then followed by 35.27 N for S2 with the ratio of 80% HDPE and 20% CaCO3, and 32.88 N for S1 with ratio of 90% HDPE and 10% CaCO3. The flexural stress and strain is shown to be the highest for S3 followed by S2 and S1. Using the flexural modulus formula, the calculation shows that S3 has the highest reading compared to S1 and S2 respectively. As the weight percentage of CaCO3 increases, the flexural stress also increases. This shows that S3 can withstand more stress that acts upon it than S1 with less CaCO3 . The data is then tabulated in graph in Fig. 2. Flexural modulus was calculated using the formula to indicate a material’s stiffness when it flexed. HDPE is originally a polymer that has high elasticity. However, due to the increasing weight percentage of CaCO3 in each of the sample, it can be concluded that the higher the amount of CaCO3 mixed with HDPE, the higher the flexural modulus of the material. HDPE has relatively high elasticity and will not break easily when stress is acted upon it. The more weight percentage of CaCO3 is Table 2 Flexural test result Sample

Max force (N)

Flexural stress, σ (MPa)

Flexural strain, ε (%)

Flexural modulus, E (GPa)

S1

32.88

19.73

8.06

2.45

S2

35.27

21.17

7.78

2.72

S3

35.83

21.50

7.76

2.77

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Fig. 2 Bar chart for flexural modulus, E versus weight percentage of CaCO3

added with HDPE, the longer the time taken for the material to achieve its maximum force [17].

3.2 Impact Test Table 3 shows the result of impact test based on the test that has been done. The test was done using three different ratios with three specimens each. The calculated impact energy and impact strength are tabulated in the table. The impact energy between the three samples gave a stable reading with differences about 0.01 J and the calculated impact strength has moderate differences of around 0.01 J/mm2 . S1 with ratio of 10% CaCO3 have the highest value for impact strength of 0.72 J/mm2 . S3 with the ratio of 30% CaCO3 and S2 with the ratio of 20% CaCO3 have the same value for impact strength of 0.71 J/mm2 . Figure 3 shows the bar chart for impact test. As analyzed, the increasing weight percentage of CaCO3 affected the impact strength of the materials. In consequence, the impact strength of the composites completely decreased. The decreasing value over the samples indicated the brittle/weak material. Table 3 Impact test result

Sample Average impact energy (J) Impact strength (J/mm2 ) S1

0.60

0.72

S2

0.59

0.71

S3

0.59

0.71

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Fig. 3 Bar chart for Impact strength versus weight percentage of CaCO3

3.3 Tensile Test Table 4 shows the result obtained for tensile test where the values of Young’s Modulus are changing according to the weight percentage of CaCO3 . S1 with 10% CaCO3 ratio has the lowest maximum force as it can bear with 259.09 N and the lowest Young’s Modulus value of 0.43 GPa. The second highest maximum force is S2 with 20% of CaCO3 ratio for 265.98 N maximum force and 0.47 GPa for Young’s Modulus value. The highest maximum force value was made by S3 with 30% of CaCO3 ratio for 291.99 N. Young’s Modulus is also known as the elastic properties of material to return back to its original shape after force is applied on it [15]. The weight percentage of CaCO3 in the sample increases the Young’s Modulus of the materials based on Fig. 4. It appears that S3 with the highest value can withstand the most maximum force applied on it compared to S1 and S2. Table 4 Tensile test result Sample

Average max force (N)

Tensile stress, σ (MPa)

Tensile strain, ε (%)

Young’s modulus, E (GPa)

S1

259.09

17.27

40.08

0.43

S2

265.98

17.73

37.37

0.47

S3

291.99

19.47

33.11

0.59

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Fig. 4 Bar chart of young’s modulus versus weight percentage of CaCO3

3.4 SEM and EDX Analysis SEM analysis of synthesized cockle shells CaCO3 powder with different magnifications to have clearer vision of the particles of (a) 150× magnification, (b) 1000× magnification and (c) 3000 magnification in Fig. 5 was compared to previous study by Hoque et al. Revealed the prepared cockle shell, CaCO3 powder has rod-like or cluster structures are shown using arrow similar as in the images of Fig. 5a and b. These rods/needle-like structures are typical aragonite. Figures 6, 7 and 8 show the structure of sample 1 containing 10% of CaCO3 ratio where less CaCO3 particles were present in the structures compared to sample 2 containing 20% of CaCO3 and sample 3 containing 30% of CaCO3 particles. Sample 3 had the most micron sized CaCO3 particles in the structures followed by sample 2 and sample 1. The results proved that the differences in weight percentage of CaCO3 were visible through SEM analysis and the samples were mixed evenly as the particles were found everywhere. Tensile test samples were scanned under 100× magnification to determine the structure after it has been pulled until failure occurred. Sample 1 in Fig. 9a showed less hair as well as less CaCO3 particles on the sample’s breaking point because it had the lowest weight percentage of CaCO3 . Sample 3 in Fig. 9c has the highest hair visible under the SEM analysis and lots of CaCO3 particles seemed to appear at the sample’s breaking point. The elemental constituents of the synthesized cockle shell, CaCO3 powder, was investigated at each spectrum found in cockle shell CaCO3 powder. Figure 10 shows the EDX result for CaCO3, . From Fig. 11, it shows that spectrums 1, 2 and 3, the peak of calcium is higher than oxygen followed by carbon. Analyzed samples were investigated at each spectrum graph, and elements such as Carbon, Oxygen and Calcium were found in each scaffold sample tested.

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Fig. 5 SEM analysis of synthesized CaCO3

3.5 FTiR Analysis Analysis using Perkin Elmer Fourier Transform Infrared machine to confirm the material contained in the samples is really mixtures of CaCO3 and HDPE. Figure 12 indicates that the samples containing polymorphs of CaCO3 ; aragonite, calcite and vaterite are based on the graph of CaCO3 [18, 19]. The phase of cockle shells CaCO3 powder was confirmed by FTiR Analysis where the spectrum showed the peak ranging from 1460 to 1473 cm−1 can be attributed to aragonite characteristics and peak range between 860.72 and 860.78 cm−1 confirming that the powder was pure aragonite. The peak ranged from 718.43 cm−1 to 718.81 cm−1 show that there were calcite and vaterite in the powder respectively. The results were compared with previous research by Hoque et al. In Fig. 13 and the FTiR analysis spectrum showed the peak of 1083 and 861.93 cm−1 that can be attributed to aragonite characteristics and peak 861.93 cm−1 confirmed that the powder was pure aragonite. Nearby peaks of 876 and 870 cm−1 confirmed that there were calcite and vaterite in the powder [9].

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Fig. 6 SEM analysis with 50× magnification for impact test

4 Conclusion The unused cockle shells were successfully extracted to CaCO3 powder and HDPE pallets were mixed with different weight percentage or ratio. 100-micron sized CaCO3 powder was produced through the crushing and grinding process of cockle shells. Three different ratios of samples; 90% HDPE and 10% CaCO3 , 80% HDPE and 20% CaCO3 and 70% HDPE and 30% CaCO3 were mixed evenly using brabender machine. Mechanical testing that has been done proved that the increasing weight percentage affected the physical and mechanical strength of the scaffold samples greatly. This research occupied and implemented the mechanical tests to predict the strength of the material and how efficient CaCO3 is as the bioceramic material in attracting the Calcium and Phosphorus minerals to encourage the development of new bone formation. Besides the suitable elements contained in the samples for biomedical use, the mechanical properties also meet the requirements to match the host bone properties and have proper load transfer especially when force is acted upon it based on previous studies.

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Fig. 7 SEM analysis with 100 × magnification for impact test

5 Recommendation Some suggestions are made for future research to get better results by: 1. Using more than 3 samples to get more accurate reading for each ratio. 2. Adding more materials besides HDPE and CaCO3 to determine which material is more suitable for biomedical use. 3. Differentiating concentration to be added to determine the properties of the materials and to have accurate values.

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Fig. 8 SEM analysis with 1000× magnification for impact test

Fig. 9 Tensile test samples under 100× magnification

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Fig. 10 EDX result of CaCO3 powders

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Ca C

Zr Zr

Ca

0 2 4 Full Scale 221 cts Cursor: 0.000

6

8

10

12

14

16

18

20 keV

(a) Sample 1 Spectrum 1

Ca C

Zr O

Zr

Ca

0 2 4 6 Full Scale 233 cts Cursor: 20.220 (0 cts)

8

10

12

14

16

18

20 keV

(b) Sample 2 Spectrum 1

Ca C

Ca O 0 2 4 6 Full Scale 125 cts Cursor: 20.220 (0 cts)

8

10

12

(c) Sample 3 Fig. 11 Element constituent in samples tested

14

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18

20 keV

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Fig. 12 Sample contains polymorphs of CaCO3 ; aragonite, calcite and vaterite

Fig. 13 FT-IR spectrum of cockle shell CaCO3 powder [9]

Acknowledgements The authors would like to thank the Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia (UTHM) for its financial support through the Short-Term Grant Scheme (STG) 1/2016 Vol. U532.

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