Hybrid Composites: Processing, Characterization and Applications [14] 9783110724660

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Kaushik Kumar and B. Sridhar Babu (Eds.) Hybrid Composites

Advanced Composites

Edited by J. Paulo Davim

Volume 14

Also of Interest Series: Advanced Composites J. Paulo Davim (Ed.) ISSN - Published titles in this series: Vol. : Plant and Animal Based Composites () Ed. by K. Kumar, J. Paulo Davim Vol. : Glass Fibre-Reinforced Polymer Composites () Ed. by J. Babu, J. Paulo Davim Vol. : Polymers and Composites Manufacturing () Ed. by K. Kumar, J. Paulo Davim Vol. : Biodegradable Composites () Ed. by Ed. by K. Kumar, J. P. Davim Vol. : Wear of Composite Materials () Ed. by J. P. Davim Vol. : Hierarchical Composite Materials () Ed. by K. Kumar, J. P. Davim Vol. : Green Composites () Ed. by J. P. Davim Vol. : Wood Composites () Ed. by A. Alfredo, J. P. Davim Vol. : Ceramic Matrix Composites () Ed. by J. P. Davim Vol. : Machinability of Fibre-Reinforced Plastics () Ed. by J. P. Davim Vol. : Metal Matrix Composites () Ed. by J. P. Davim Vol. : Biomedical Composites () Ed. by J. P. Davim Vol. : Nanocomposites () Ed. by J. P. Davim, C. A. Charitidis

Hybrid Composites Processing, Characterization, and Applications Edited by Kaushik Kumar and B. Sridhar Babu

Editors Dr. Kaushik Kumar Birla Institute of Technology Department of Mechanical Engineering Mesra, Ranchi, Jharkhand 835215 India [email protected] Dr. B. Sridhar Babu SV College of Engineering and Technology, RVS Nager, Tirupathi Road, Chittoor Andhra Pradesh, INDIA-517127 [email protected]

ISBN 978-3-11-072466-0 e-ISBN (PDF) 978-3-11-072468-4 e-ISBN (EPUB) 978-3-11-072485-1 ISSN 2192-8983 Library of Congress Control Number: 2022945935 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2022 Walter de Gruyter GmbH, Berlin/Boston Cover image: gettyimages/thinkstockphotos, Abalone Shell Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Preface The editors are pleased to present the book Hybrid Composites: Processing, Characterization and Applications under the book series Advanced Composites. The book title was chosen as it depicts upcoming trends in composite materials for the next decade. This book is a compilation of different types of simultaneous reinforcement in various matrixes or in common words hybrid composites. Emphasis is being made toward the achievements, progress, and recent developments and applications of them. Hybrid composites have exceptionally advanced features that can be used to convene required design necessities in a nice and cost-effective way compared to nonhybrid composites. These materials have more advantages over conventional composites like excellent stiffness, balanced strength, improved bending and mechanical properties, improved fatigue/impact resistance, reduced notch sensitivity, reduced weight and/or cost, improved fracture toughness and/or crack arresting properties, and balanced thermal distortion stability. Researchers are very much fascinated by the hybrid composites for their performance in engineering applications. They provide a fertile materials science research field aiming to achieve a better understanding of the interplay between industrial processing, microstructure development, and the resulting material properties. This book covers the latest developments in the hybrid composite materials, processing, characterization of innovative microstructure and process design concepts, and advanced characterization techniques combined with modeling of materials behavior. In present time, “Hybrid Composite” is the key for major discipline, and many researchers and scholars are working in these areas. This book provides an insight for all researchers, academicians, postgraduate, or senior undergraduate students working in the area. The chapters in the book have been provided by researchers and academicians working in the field and have gained considerable success in the field. The chapters in the book have been categorized into three sections namely Section I: State-of-the-Art; Section II: Synthesis and Characterization; and Section III: Applications and Analysis. Section I contains Chapter 1, whereas Section II has Chapter 2, and Section III from Chapter 3 to Chapter 7 Section I starts with Chapter 1 providing a comprehensive review of hybrid composites with emphasis on processing, characterization, and applications. The chapter focuses on reviewing the production of the hybrid composites which are discussed in the most current context, with processing, characterization, and applications as the primary focus. Finally, the chapter provides a summary of the current state of technology used for hybrid composite materials in terms of raw materials used and their properties, as well as an outline of some of the important hybrid composites with an emphasis on their diverse applications along with the use of smart hybrid composites.

https://doi.org/10.1515/9783110724684-202

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Again, Chapter 2, the only chapter of Section II, educates on the synthesis and characterization of Carbon Nanotube/Polyhedral Oligomeric Silsesquioxane hybrid nanocomposites. In this chapter, multiwalled carbon nanotubes (CNTs) coated with functionalized Polyhedral Oligomeric Silsesquioxanes (POSS) were studied as potential polymer fillers. A straightforward sonochemical method is used to coat CNTs with four different types of POSS® functionalized materials: a) Glycidyl Ethyl (GE)POSS, b) OctaIsobutyl (OI)-POSS, c) Epoxy Cyclohexyl (EC)-POSS, and d) Glycidyl Isooctyl (GI)-POSS. Surface coating of CNTs with POSS was analyzed using FourierTransform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and High-Resolution Transmission Electron Microscopy (HRTEM). The FTIR results indicated that the epoxy rings may be open and attached to the surface of CNTs in the case of EC-POSS. XPS results show the decrease of carbon upon coating of POSS as compared to the pristine CNTs. The percentage of decrease in carbon atom upon coating is ~−6%, −12%, and −18% for OI-POSS, GI-POSS, and GE-POSS, respectively. TGA analyses show the ~ 75 wt%, 50 wt%, and 23 wt% coverage of GE-POSS, EC-POSS, and GI-POSS on CNTs, respectively. HRTEM confirms the uniform coating of the POSS on CNTs. The chapter concludes that these various types of coatings of POSS on CNTs can be used as potential polymer fillers for lightweight high strength polymer nanocomposites. Chapter 3, the next chapter of the book and the first chapter of Section III, provides insight into the viscoelastic response of hybrid polymeric dental composites in sliding contacts and applications. This is observed and analyzed with respect to the sliding speed, material composition, and geometry. It can be concluded that polymeric solids produce their own distinct viscoelastic signatures that cause resonance at certain sliding speeds which can be explained by resonance conditions for electromagnetic waves. The observed viscoelastic phenomenon is characterized with respect to the relaxation and recovery times for rigid polymeric solids. It is confirmatory as a demonstration of proof of existence of viscoelasticity and selforganization in these materials under sliding contact conditions. Viscoelastic observations are also made on the aged specimens in sliding contact. Chapter 4 investigates on mechanical properties of rice straws and rice husk reinforced hybrid polymeric composite. The work is a noble effort taken toward the development of rice straw (RS) and rice husk (RH) embedded hybrid polymer composite materials. This primarily has two targets: a. Agricultural wastes like RS and RH as natural fiber have been utilized for the development of such RS–RH-reinforced hybrid composites, i.e. waste utilization. b. They are biodegradable in nature, i.e. environment friendly. This chapter also indicates the enormous increase “in mechanical properties such as tensile strength, flexural strength, flexural modulus, and young’s modulus (E)” of the prepared composite samples having a single layer, double layers, and triple

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layers of fibers (RS+RH) reinforcements oriented in unidirectional and in a bidirectional manner. In Chapter 5, the next chapter of the book, advanced computational simulation has been applied to various lightweight composite materials under complex load for optimizations. This chapter provides solution based on continuum mechanics and has employed numerical analysis mostly. So, the chapter deals with the aerodynamic load-based impact analysis on various composites with the help of FSI analysis. The one-way coupling-based approach has been investigated at subsonic speeds through advanced computational simulations. ANSYS Fluent is predominantly involved in the estimation of Aerodynamic Pressure load on the conventional test specimen. Additionally, ANSYS Design Modeler tool is used for conceptual design construction, and the various composites are generated in ANSYS ACP tool. Finally, the comparative Impact analyses are executed and thereby the suitable material for impact application was selected. In the next chapter, i.e., Chapter 6, an orthopedic application of hybrid composites has been described. Orthotic Callipers, a support system used by polio patients, have been fabricated with help of polymer matrix reinforced with graphene and coir fiber at both levels (macro and micro). Graphene and coir fiber are used as hybrid reinforcement and epoxy resin as a matrix to replace aluminum-based callipers which are currently used as an alternate material for polio survivors. Coir fibers were reinforced by hand lay-up technique and graphene was dispersed using an ultrasonic sonicator. To ensure void-free samples, fabrication was carried out under vacuum. Tensile testing and flexural properties were estimated and then results were compared with commercially used aluminum-based orthotic callipers. The current investigation exhibits the higher strength with relatively lower density with such natural fibers reinforced hybrid composites. The last chapter of Section III and the book, i.e., Chapter 7 presents optimization of mechanical and wear properties of AL7075 SiC and graphite hybrid composite using Utility Additives Method. Metal Matrix Composites (MMCs) are new-generation materials that are widely used for various advanced applications, viz. aerospace automotive thermal, structural, electronics, and owing to their superiority over the conventional materials. Their specific modulus, their specific strength, wear resistance, chemical inertness, high-temperature stability, regulated thermal expansion coefficient, etc. are much stronger. Among the several alternatives available, aluminum has to be the most widely used metal for matrix applications due to its lightweight and high strength. In this chapter, graphite and silicon carbide have been used as reinforcement in MMC aluminum. Graphite has a lubrication feature that reduces wear and friction, and it also possesses high resistance to corrosion, resulting in a long life of the components. Silicon Carbide provides exceptional strength, hightemperature stability, oxidation resistance, and corrosion resistance. The effect of Graphite and Silicon Carbide reinforcement on aluminum metal and matrix composite has been analyzed. Taguchi orthogonal array was used for the experiment. The result

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of the wear test was then optimized using the Utility Additive Method. The microstructure of the composite material SEM micrograph has been provided for analysis. First and foremost, we would like to thank God. It was your blessing that provided us the strength to believe in passion, hard work, and pursue dreams. We thank our families for having patience with us for taking yet another challenge which decreases the amount of time we could spend with them. They were our inspiration and motivation. We would like to thank our parents and grandparents for allowing us to follow our ambitions. We would like to thank all the contributing authors as they are the pillars of this structure. We would also like to thank them to have belief in us. We would like to thank all of our colleagues and friends in different parts of the world for sharing ideas in shaping our thoughts. Our efforts will come to a level of satisfaction if the professionals concerned with all the fields related to hybrid composite materials get benefitted. We owe a huge thanks to all of our technical reviewers, Editorial Advisory Board Members, Book Development Editor, and the team of Walter de Gruyter GmbH for their availability for work on this huge project. All of their efforts were instrumental in compiling this book, and without their constant and consistent guidance, support, and cooperation we wouldn’t have reached this milestone. Especially, during this global pandemic, when all support were withdrawn, we were elated to find the whole team of Walter de Gruyter GmbH by our side to support. We salute their dedication. Last, but definitely not least, we would like to thank all individuals who had taken time out and helped us during the process of editing this book; without their support and encouragement we would have probably given up the project. Kaushik Kumar B. Sridhar Babu

Contents Preface

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List of contributors About the editors

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Part I: State-of-the-art Yashwanth Padarthi, Raghu Raja Pandiyan Kuppusamy A comprehensive review on hybrid composites: processing, characterization, and applications 3

Part II: Synthesis and characterization Wanda D. Jones, Bedanga Sapkota, Shaik Jeelani, Tarig A. Hassan, Melissa Hines, Vinod Dhanak, Vijaya K. Rangari Synthesis and characterization of carbon nanotube/polyhedral oligomeric silsesquioxane hybrid nanocomposites 23

Part III: Applications and analysis Padmanabhan Krishnan Viscoelastic response of hybrid polymeric dental composites in sliding contacts and applications 43 Ranjan Kumar, Chikesh Ranjan, Kaushik Kumar Investigation of mechanical properties of rice straws and rice husk reinforced hybrid polymeric composite 59 Vijayanandh R., Raj Kumar G., Arul Prakash R., Senthil Kumar M., Indira Prasanth S., Kesavan K., Balasubramanian S. Optimizations on various lightweight composite materials under complex load using advanced computational simulation 81

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Nisha Kumari, Kaushik Kumar Investigations of mechanical properties of a hybrid nanocomposite for the development of lower body orthotic callipers 103 Mohan Kumar Pradhan, Shubham Gupta Mechanical and wear properties of AL7075 Sic and graphite hybrid composite and optimization using utility additives method 117 Subject index

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List of contributors Yashwanth Padarthi Indian Institute of Technology, Kharagpur, INDIA

Vijayanandh R. Kumaraguru College of Technology, Coimbatore, INDIA

Raghu Raja Pandiyan Kuppusamy National Institute of Technology, Warangal, INDIA

Raj Kumar G. Kumaraguru College of Technology, Coimbatore, INDIA

Wanda D. Jones Cornell University, Ithaca, NY, USA

Arul Prakash R. Kumaraguru College of Technology, Coimbatore, INDIA

Bedanga Sapkota Tuskegee University, Tuskegee, AL, USA Shaik Jeelani Tuskegee University, Tuskegee, AL, USA Tarig A. Hassan Tuskegee University, Tuskegee, AL, USA Melissa Hines Cornell University, Ithaca, NY, USA Vinod Dhanak University of Liverpool, Liverpool, UK Vijaya K. Rangari Tuskegee University Tuskegee, AL, USA Padmanabhan Krishnan Vellore Institute of Technology, Vellore, INDIA Ranjan Kumar Birla Institute of Technology, Mesra, INDIA Chikesh Ranjan Birla Institute of Technology, Mesra, INDIA Kaushik Kumar Birla Institute of Technology, Mesra, INDIA

https://doi.org/10.1515/9783110724684-204

Senthil Kumar M. Kumaraguru College of Technology, Coimbatore, INDIA Indira Prasanth S. Kumaraguru College of Technology, Coimbatore, INDIA Kesavan K. Kumaraguru College of Technology, Coimbatore, INDIA Balasubramanian S. Kumaraguru College of Technology, Coimbatore, INDIA Nisha Kumari Medi-Caps University, Indore, INDIA Mohan Kumar Pradhan Maulana Azad National Institute of Technology, Bhopal, INDIA Shubham Gupta Maulana Azad National Institute of Technology, Bhopal, INDIA

About the editors Kaushik Kumar, B.Tech (Mechanical Engineering, REC (Now NIT), Warangal), MBA (Marketing, IGNOU) and Ph.D. (Engineering, Jadavpur University), is Associate Professor in the Department of Mechanical Engineering, Birla Institute of Technology, Mesra, Ranchi, India. He has 20 years of teaching and research and over 11 years of industrial experience in a manufacturing unit of global repute. His areas of teaching and research interest are Composites, Optimization, Nonconventional machining, CAD / CAM, Rapid Prototyping, and Quality Management Systems. He has 14 patents, 60+ books, 30+ edited book volumes, 65+ book chapters, 180+ international journal articles, and 21 international and 1 national conference publications to his credit. He is on the editorial board and review panel of many international and national journals of repute. He has been felicitated with many awards and honors. B. Sridhar Babu has completed B.E. in Mechanical Engineering from Kakatiya University, M.Tech. in Advanced Manufacturing Systems from JNTUH University, and Ph.D. in Mechanical Engineering from JNTUH University. He has 23 years of teaching experience. He joined the Department of Mechanical Engineering, Sri Venkateshwara College of Engineering and Technology Chittoor on December 1, 2021. He is Fellow of the Institution of Engineers (I), Kolkata, and also Member of ISTE, IAENG, and SAE India. He has published 38 papers in various international/nNational journals and international/national conferences. He is author of 4 textbooks. He received Bharath Jyothi award for his research excellence from India International Friendship Society, New Delhi, India. He is a paper-setter for various universities, a reviewer for various international journals and conferences, and has guided more than 75 B.Tech. and M.Tech. projects. His research interests include Manufacturing, Advanced Materials, and Mechanics of Materials, etc. He is a guest editor for Proceedings of First and Second International Conference on Manufacturing, Material Science and Engineering (ICMMSE’19; 20), Materials Today – Proceedings (Scopus and CPCI Indexed) and AIP Proceedings (Scopus Indexed).

https://doi.org/10.1515/9783110724684-205

Part I: State-of-the-art

Yashwanth Padarthi, Raghu Raja Pandiyan Kuppusamy

A comprehensive review on hybrid composites: processing, characterization, and applications Abstract: Composite materials are now widely used in aircraft, military, vehicles, sports, and medical industries. However, the majority of commercially available composites are made from components derived from fossil fuels, which are quickly decreasing and are a major source of environmental pollution. Besides harming the environment, majority of these composites are non-biodegradable and finally disposed in landfills. In order to effectively resolve these issues, it is inevitable that sustainable alternatives such as bio-based composite materials with eco-friendly end-of-life be developed. A wide range of applications of the composite structures paved the path for a significant amount of research in order to investigate various strategies for improving their overall performance. One such effective strategy is hybridization, which can lead to improvements in the chemo-mechanical properties and the performance of the composites. Hybrid composites have numerous distinct advantages and enormous potential in a multitude of uses with substantial impact on practical applications. Thus, the study presented focuses on reviewing the production of the hybrid composites, which are discussed in the most current context, with processing, characterization, and applications as the primary focus. Finally, this work also provides a summary of the current state technology used for hybrid composite materials in terms of raw materials and their properties as well as an outline of some of the important hybrid composites with an emphasis on their diverse applications along with the use of smart hybrid composites. Keywords: hybridization, tailor-made properties, chemo-mechanical properties, bio-based composites, smart hybrid materials

1 Introduction Composites are multiphase substances that exhibit significant usage in industries with their excellent properties: low density, good strength, and high specific stiffness

Yashwanth Padarthi, Department of Chemical Engineering, Indian Institute of Technology, Kharagpur 721302, India Raghu Raja Pandiyan Kuppusamy, Department of Chemical Engineering, National Institute of Technology Warangal, Telangana 506004, India, e-mail: [email protected] https://doi.org/10.1515/9783110724684-001

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[1, 2]. They are the most substantial alternatives to other structural materials such as steel, which is used in numerous large-scale applications. The metrics used to assess these properties are specific strength and specific modulus. As it is well known, the composites have two elements: dispersed phase (fiber-reinforced ingredients) and matrix [3]. Fibers/fabrics serve as reinforcing constituents in fiber-reinforced composites. Fillers and additives are occasionally used as ingredients to minimize costs while improving attributes such as fire resistance, ultra violet radiation resistance, electrical conductance, and mechanical performance of composites. Reinforcements also influence the properties of the composite material [4]. The controlling variables in defining the characteristics of a fiber-reinforced composite are the matrix, fiber, and the interfacial region. The fiber and matrix are the two most important components of every fiber-reinforced composite, along with their characteristics that are critical in defining the properties of the fiber-reinforced composites [5]. The mechanical and chemical properties of the interphase region vary from those of the fiber and matrix. Therefore, it has a substantial influence on the characteristics of the composites. Composites outperform traditional designed materials in various ways, including greater specific strength, better stiffness, and improved weathering resistance besides superior fatigue properties [6]. Composites are often applied in large-scale structures along with various constructions like in ship outer surface, automobile bodywork, and in bathing tubs with aerospace and offshore structures being the most intricate uses of such materials exposed to a challenging environment [7]. Thus, composites are categorized based on the type of reinforcement utilized and the matrix employed. Nobody is unfamiliar with the term composite; it has been used from primeval eras; first manufactured composites, going back to more than 6000 years [8]. The primary composites initially were made of wood, bamboo, calf tendons, and horns [9]. Chemical discoveries fueled the development of plastics in the early nineteenth century; materials such as polyester, vinyl, and others were invented, and Bakelite became the first synthetic plastic in the late 1990s [10]. In 1936, fiber-reinforced polymer (FRP) introduced a new dimension to the composite industry, and in 1938, better performance resin systems such as epoxies were accessible [11]. The necessity for materials with high specific strength, better stiffness moved the composite production from research to manufacture during WWII as well as a complete composite vehicle developed in 1947 [12]. In an era where technology is always evolving, it is difficult to find a material that combines every essential properties as giving rise to a new substance known as composite [13]. However, it has been demonstrated that addition of hybrid materials significantly affects the performance such as increase in strength or stiffness [14]. In fiber-reinforced composites, fiber reinforcements influence the performance that can change the final mechanical properties [15]. There are also multiple variants available to enhance the hybridization, with interlayers that are used to improve the mechanical

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properties. Composites comprising reinforcement dimensions however differ in three, which is why they are called orthotropic or transversely isotropic materials. The following is an explanation for the need for hybridization: Carbon fiber (CF) is a great material owing to its strength and other beneficial features, and it is utilized in many technical applications such as aviation structures, locomotives, and other transportation infrastructure [16]. CF, on the other hand, has excellent mechanical properties that can quickly impact the performance and helps in effective usage of hybridization [17]. Fragility of the composites may be effortlessly improved by hybridization by the replacement of certain detrimental parts such as the carbon-woven fabric with ductile fiber layers [18]. Hybrid composites have lately garnered a lot of attention; created behavior is totally dependent on the properties of the reinforcing components. Composites are essentially textile in nature, and their performance vary in proportion to thickness [19]. Furthermore, as compared to conventional composites, hybrid composite manufacture boosts the performance along with minimization of capital expenditure [20]. The durability of FRP composites is determined by the matrix-to-fiber ratio, the crucial element being the matrix which is responsible to uniformly distribute the load applied on the hybrid composite structure. Several investigations on hybrid composites based on various combinations are being conducted as discussed in detail below.

2 Recent research in hybrid composites: processing, characterization, and applications Barouni et al [21] investigated the epoxy-based hybrid composite, which were intended to take use of the synergistic effects of flax and glass fiber (GF) hybridization to achieve excellent mechanical performance. Composites constructed solely of flax fibers as well as randomized flax and glass reinforcements in different layers were produced to explore the fatigue behavior. The performance of hybrid laminates studied showed encouraging results, with the hybrid design having a substantial effect on mechanical strength. The hybrid composite with randomized glass and flax reinforcements outperformed the other two laminates in terms of fatigue performance, with an excellent damage inhibition behavior. Accordingly, as studied from the statistical analysis, the composite demonstrated a lower failure withstanding damage. The imaging techniques can be perfectly utilized to analyse the effect of fatigue life which could produce faults along the fibre matrix interface. The research contributes to the use of hybrid composites and fully deciphers the degradation along with the impact of the defects inherent in the functioning of hybrid composites.

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Di Benedetto et al [22] manufactured CF/poly ether-ether-ketone (PEEK) hybrid composites. The filament-winding technique was altered for allowing the winding of CF/PEEK composites using various configurations of the braided metal meshes that were subsequently thermoformed. Thermal characterization was utilized to determine the thermal expansion and glass transitions inherent in the CF/PEEK composites. The inclusion of wire mesh does not affect the thermal characterization of the CF/PEEK composites, and their use is not limited by temperature variations. The hybrid metal composite enhanced interlaminar shear strength by 22.7% when compared with other hybrid composite in the absence of braided metal mesh. Pseudo-ductility was investigated by Czel [23] of hybrid composites with various configurations of the reinforcements. When equated with the predicted modulus of elasticity of the S-glass/epoxy hybrid composites (cross-ply), stiffness improvements of 20–70% were obtained. A pseudo-ductile stress–strain response with clearly visible initiation of damage was identified in every orientation. The laminates manufactured were found to be appropriately aimed at manufacturing without the necessity of any specialized apparatus. Sałasińska et al [24] explored the fabrication of hybrid-layered composites that allows for extensive adjustment of their characteristics as well as adaptability to final expectations. The hybrid composites were created using a variety of techniques including manual lay-up, vacuum bagging, and resin injection. Various configurations of fabrics were utilized to construct composites. Flexural, impact behavior, and other characterizations were utilized to study the impact of production process and fabric arrangement on the performance behavior of hybrid composites. The vacuum-bagged composites produced the least amount of smoke and were the least flammable. It was concluded that the hybrid composites produced by vacuum bagging technique could increase the fire retardance while keeping other mechanical properties intact which are best suited for applications such as railways and automobiles. Neto et al [25] reviewed natural fiber-reinforced polymer composites (NFRCs) for a wide range of applications in a variety of engineering purposes owing to advantages over conventional composites. However, because of the hydrophilic nature of the NF, the NFRCs have relatively poor mechanical properties and humidity absorption. The authors suggested that hybridization is the best method to boost the performance of NFRCs. Thus, analysis of their properties and the possibilities of mixing different reinforcing ingredients to generate hybrid composites is thus of immense potential, along with an overview of current successes in hybrid natural NFRCs. First, the major factors impacting hybrid fiber-reinforced composite performance were explored briefly. Last, water uptake properties of hybrid fiber-reinforced composites are investigated. Recent breakthroughs in fiber treatment and modification, as well as product innovation, have solved some of these difficulties (hybridization). Mohit et al [26] reviewed the use of plant fibers in polymer laminates that has had a considerable impact on environmental implications with the growing interest in bio-based materials. Hybrid laminates are composed of two or more types of plant

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fibers derived from lignocellulosic components and are used in a variety of applications including nonstructural and structural laminates, cars, utensils, and aerospace parts. These composites based on plant fibers were the recognized candidates intended for greater efficiency, sustainability, low cost, eco-friendly, and lightweight composites. The authors reviewed the several plant-based hybrid composites that were employed to generate ecologically sustainable composite materials. Plant-based hybrid composites combine the advantages of sustainability with a long-term benefits such as at its disposal at the end of the lifecycle of the hybrid composites. Because the massive production of petroleum-based polymers endangers our environment and oil supply, Ullah et al [27] investigated the poly(lactic acid) (PLA) hybrid composites. In the recent decades, researchers have focused on the use of biodegradable polymers rather than synthetic polymers for a wide range of commercial, industrial, and medical uses. Although PLA is widely regarded as the best alternative to the traditional composites due to its superior mechanical performance, low capital expenditure, and nontoxicity, it has significant limits for a variety of end uses due to its slow crystallization rate and bad mechanical performance. Over the last two decades, researchers have devised a variety of methods for customizing the properties of PLA, such as combining it using nanofillers. Polyhedral oligomeric silsesquioxane (POSS) was identified to be the effective nanofiller among all nanofillers, such as carbon nanotubes and organoclays, because it efficiently disperses inside the matrix of the PLA hybrid composites. The research was performed addressing the integration of POSS inside PLA or PLA mixtures in order to analyse the chemo-mechanical properties of the enhanced composites with that of the neat PLA. To enhance the recyclable polypropylene by melt-mixing and injection-molding, Yuan et al [28] employed tobacco stalk flour (TSF) and magnesium oxysulfate whiskers as fillers. The morphological analysis on hybrid composites found that the TSF and recycled polypropylene (rPP) had strong adhesion, which increases composite mechanical performance. Addition of TSF has not resulted in any substantial increase of the rPP-based composites’ tensile strength; however, it did significantly improve its flexural modulus. The authors found that the addition of 30 wt% TSF to the rPP increased the flexural modulus by 32% than the neat rPP. The magnesium oxysulfate whiskers as fillers improved the material’s performance even further. The crystallization temperature and crystallinity of the polymer rise as the amount of TSF in the rPP increases. Moreover, the inclusion of TSF increased the hybrid composites’ water absorption and antibacterial performance on account of the hydrophilicity and antibacterial capability of TSF. As a consequence of the experiments conducted, a novel method for TSF recycling and usage has been developed. Utilizing a Biopoxy matrix, Rangappa et al [29] created hybrid composites using chicken feathers as fillers with the reinforcements of lignocellulose Ceiba Pentandra bark fibers. The mechanical performance of Ceiba Pentandra bark fiber filler-reinforced carbon fabric-layered bioepoxy hybrid composites was the best among the manufactured hybrid composites. The composites demonstrated strong interfacial

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adhesion especially according to scanning electron microscope (SEM) images. The thermogravimetric analysis depicted that both the hybrid composites deteriorate in many stages while remaining stable up to 300 °C. The thermomechanical tests demonstrated that the hybrid composites were dimensionally stable. In terms of thermal and mechanical performance, the examined composites outperform simple bioepoxy or nonbioepoxy thermosets and are apt for semi-structural end-uses. Banga et al [30] created a ZIF-8/GO hybrid composite that assesses carene vapors which are altered with the respiratory ailments. The authors suggested that electrochemical sensor platform detects the target analyte utilizing ZIF-8/GO that offers substantial benefits for gas sensing in terms of diffusive porosity, specific surface area, and extraordinary electro-chemical activity. At 100 parts per billion, the ZIF-8/GO-modified sensor system provides the best sensitive analysis for the detection of the carene vapors. The findings pave the way for the creation of a breathomics-enabled electrochemical approach for point-of-care diagnostics. The sensing carene platform might be used to detect diseases in the respiratory tract at the lower sections. Biswal et al [31] used a solid-state manufacturing technique to create an aluminum (Al)-based hybrid composites, where WS2 was used as a reinforcement. The mechanical and structural performance of novel Al-based hybrid composites along with the effect of WS2 reinforcement was investigated in order to optimize the composition of the generated hybrid composite. The density of hybrid composites improved to 2.86 g/cm3 from the initial density of 2.73 g/cm3. When the WS2 wt% increases in the matrix phase, the resultant average hardness of the hybrid composites amplified from 33.3 HV to a value of 52.2 HV. Lim et al [32] explored the use of hexagonal boron nitrides (h-BNs) as fillers on account of good thermal conductivity of the h-BN. However, considerable loading of the h-BN fillers in the hybrid composites is problematic as it significantly increases the h-BN hybrid composites viscosity along with limiting the processing capability of h-BN composites. The authors addressed this problem using an epoxyorganosiloxane and spherical aluminium oxides to improve the loading of h-BN in hybrid composites. Yao et al [33] investigated the steel–CF-reinforced plastic (CFRP) hybrid composites manufactured utilizing a variety of processes to illustrate the effect of an intermediate adhesive layer on its fracture toughness. The test results of double cantilever beam and end-notched flexure validate that inserting an intermediate adhesive layer at the interface of the steel–CFRP hybrid composites can increase the interfacial fracture toughness. The hybrid composites predominantly exhibit failure in Mode I at the interface of the fiber and the epoxy, whereas failure under Mode II loading occurs at the adhesive especially at the interface of the steel and the CFRP interface. Angin et al [34] investigated the performance of hybrid PLA composites using alkyl ketene dimer (AKD) and their chemo-mechanical properties. The PLA hybrid composites were created via extrusion subsequently with hot press molding. With the addition of AKD, the degree of crystallinity of the NF/GF/PLA (10/20/70) increased to

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54.4%, which was 18.4% higher than the clean PLA. The inclusion of AKD, on the other hand, had no impact on the temperature of degradation of the PLA hybrid composites. The inclusion of AKD lowered the heat deflection temperature of PLA hybrid composites based on the type of the filler. The addition of AKD decreased the thermal conductivity of the GF/PLA (30/70) composites. Liu et al [35] developed a two-step procedure to create a variety of manganese oxides/porous carbon (MnxOy@C) hybrid composites. It has been revealed that the dielectric properties of absorbers are affected differently by various manganese oxides. The development of electromagnetic (EM) wave absorption (EMA) materials is a productive technique for dealing the rising contamination of the EM waves. The authors established that the inclusion of porous carbon is critical for improving the EMA (EM wave absorption) performance of hybrid composites as it allows more EM waves to reach the absorber and offers conduit for electronic transport, allowing them to benefit from conductive loss. Furthermore, distinct heterogeneous interfaces, such as porous carbon and manganese oxide, are favorable to the contribution of interface polarization. The novel design of hybrid EMA composite materials and extensive analysis of EM energy attenuation processes will demonstrate the importance of high-performance EMA materials. Aghdam et al [36] used a micromechanical approach to investigate the heat transport behavior of unidirectional hybrid composites (UHCs). The authors found that the continuous CFs embedded in the epoxy resin modified with graphene nano-platelets enhanced the heat transfer capabilities for UHCs. Hassan et al [37] investigated the carbon/ramie fiber hybrid composites, the orientation, and the stacking sequence of the ramie fiber in order to see how they affect the impact behavior. According to the findings, the hybrid composite with five ramie fiber layers absorbs more energy of around 114 J at a rate of indentation of 20 mm/min on the carbon/ramie fiber-reinforced epoxy hybrid composite. Rangaraj et al [38] investigated the hybrid composites using epoxy as the matrix with various NFs as reinforcements. The compression molding procedure was utilized to make hybrid composites based on the weight fraction of the fibers. The hybrid composites, which comprise 20 wt% snake grass and 10 wt% areca fiber, exhibit significant mechanical performance with the highest tensile, flexural, and impact strength, respectively. The results reveal that alkaline-treated fiber composites containing 20 wt% snake grass fiber outperform fiber composites without any treatment in terms of mechanical properties due to increased adhesion between the fiber and the matrix. Jena et al [39] explored the manufacturing and testing of a new epoxy composite reinforced with vetiver grass fiber (VF) and red mud (RM). By adjusting the percentages of vetiver grass and RM, five types of composites were created. The results of dry sliding wear experiments suggest that increasing the amount of RM improved both mechanical and wear properties. Fiber–matrix debonding, numerous fractures, fiber fracture, fiber pullout, debris development, and wear scars were analyzed using SEM micrographs of worn surfaces.

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Yashwanth Padarthi, Raghu Raja Pandiyan Kuppusamy

Nampoothiri et al [40] produced tri-layer hybrid composite systems of kenaf/Indian almond/kenaf (K/I/K) and Indian almond/kenaf/Indian almond (I/K/I). Mechanical characterization results of K/I/K composite validated the high flexural strength and tensile strength on account of the strong outer kenaf fiber layer, whereas the I/K/I composite had high impact strength on account of the outer Indian almond fiber layer on account of the cracks present on the outer surface. The experimental tests revealed the potential of K/I/K composite that can be utilized in scaled-up structures owing to its good mechanical performance, whilst the I/K/I composite is best suited for damping conditions because of its greater impact strength. Sharma et al [41] examined the hybridization behavior and applications of hybrid fiber-reinforced composites. Rapid industrialization and the demand for low-density materials encouraged material advancement for the goal of engineering material sustainability. Composites have played an important role in engineering materials since ancient times, but requirements for such materials, particularly FRP composites, are rising merely to develop the material quality and lifecycle. The current study comprises a comprehensive analysis of the literature on hybrid FRP composites, fabrication techniques, machining, and mechanical property alteration due to hybridization. The authors found that the most common reinforcements used in fiber-reinforced polymeric composites are Kevlar fiber, basalt fiber, CF, and GF-reinforced polymeric composites. Murali et al [42] investigated hybrid composites using aloe vera, palm, bamboo, and Kevlar as reinforcements and epoxy as the matrix material manufactured using a vacuum-assisted compression molding process. The effect of several stacking sequences on the dry sliding wear behaviors was investigated, and the optimal parameters were also discovered using the gray relational analysis: sliding velocity – 3 m/s, load – 5 N, and distance of sliding – 1500 m. Mohammed et al [43] explored that the need for lightweight materials with superior tribo-mechanical characteristics is always increasing as a result of fast technological breakthroughs. One approach pursued by researchers to achieve these desired qualities is the creation of composite materials. Aluminium hybrid nanocomposites comprising alumina (10 vol% Al2O3) and varied loadings of graphene oxide (GO) were synthesized. The hybrid composites’ tribological behavior was evaluated utilizing wear tests at 3 N load and 0.1 m/s sliding speed. The hybrid composite of 10 vol% Al2O3 with 0.25 wt% GO displayed 48% increased hardness along with 55% drop in specific wear rate and 5% decrease in COF. Parveen et al [44] examined the tensile stress-sensing capabilities of hybrid composites comprising short CFs and carbon nanofibers (MWCNTs). The cabon fiber-based composites with 0.25% CF content demonstrated the maximum sensitivity to stress. Biricik et al [45] employed flax fiber char (CH) as a reinforcing element alongside CF to create polyamide 66 (PA66) hybrid composites. The hybrid composite materials

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were characterized using thermal and mechanical analysis along with the moisture uptake. The fracture surface of the specimens was also studied using scanning electron microscopy. The findings demonstrated that silane-modified CF and CH improved the crystallization behavior, boosting the final mechanical performance of the PA66 hybrid composites. Furthermore, interfacial interactions increased the thermal stability and reduced the water absorption capacity in CH-containing composites. In conclusion, CH may be an economical replacement for the CF in PA66 at a 50:50 w/w total reinforcement (10 wt%) ratio without altering the performance of the final hybrid composite. Agrawal et al [46] investigated the epoxy-based hybrid composites containing boron nitride along with the sisal fiber (SF). The results show that adding hBN enhanced the thermal conductivity of epoxy and the dielectric constant significantly, but adding SF diminished the thermal conductivity and the dielectric constant marginally. When 30 wt% hBN and 3 wt% SF are combined, the highest thermal conductivity of 1.88 W/m K is attained. The dielectric constant for the same mixture at 1 GHz is 4.57, which is nearly comparable to clean epoxy. When ceramic filler and NF combinations are employed in the epoxy matrix, the chemo-mechanical properties enhanced. Because of their remarkable comprehensive properties, epoxy/hBN/ SF composites have discovered prospective applications in a wide range of microelectronic applications. Saha et al [47] manufactured Al-based hybrid composites with hard ceramic particles using metallic reinforcements. According to comprehensive microstructural analysis, the interfacial reaction efficiently integrated the metallic copper particles with low intermetallic generation. Mechanical properties were evaluated using macro-hardness and depth-sensing nano-indentation techniques. When compared with Al-based composites, the Al-27 wt%, Cup-5 wt%, and SiCp-5 wt%, TiCp hybrid composite has an extraordinary specific hardness and Young’s modulus. This is owing to the creation of a one-of-a-kind microstructure made up of subparticles in an extremely substructured Al-based matrix with a high dislocation density (6.63 m−2). The depth-sensing nano-indentation approach is used to further examine the matrix’s elasto-plastic characteristics. Jana et al [48] investigated the metal matrix composites (MMCs) of up to 70% SiC and 10% graphite. The MMCs’ C11 elastic constant was determined using nondestructive ultrasonic phase spectroscopy, and the findings were compared to existing micromechanical models for particle-reinforced composites. MMCs’ thermal shock resistance was evaluated by heating the metal matrix composites (MMC) in air to 500 °C and then quenching them in water 10 times. A variety of factors, including SiC concentration, graphite content, and residual porosity, have been shown to influence MMC, the thermal shock resistance. While the loss of mechanical performance of Al–SiC MMCs on account of graphite addition is anticipated, new research indicated that adding graphite also impairs the MMC’s resistance to thermal shock.

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Yashwanth Padarthi, Raghu Raja Pandiyan Kuppusamy

Wang et al [49] manufactured the hybrid composites of GPEP@PW using an epoxy (EP), graphene oxide (GP), and paraffin wax (PW). At various near-infrared intensities, the light response behavior of the tribologic properties was examined. The coefficients of friction of the hybrid composites produced using conventional fillers and the structural design are frequently uncontrolled, which makes it more challenging to meet the expectations in the contemporary industrial applications for a simultaneous real-time response behavior of these hybrid composites to external light stimulus intelligently. Finally, the manufacturing process is apt by offering a unique approach to the fabrication of light stimulus–responsive materials with smart tribological properties. Nayak et al [50] manufactured hybrid composites using areca sheath and Moringa oleifera fruit fibers as reinforcements with injection molding. The authors developed areca sheath fiber/polyethylene terephthalate (PET) composites (AF composites), Moringa oleifera fruit fiber/PET composites (MF composites), and areca/moringa PET composites (AM composites) in this study along with neat PET composites for the sake of comparison. Physical parameters such as percentage of voids and the micro-hardness characterization were investigated as well as the mechanical characterization such as impact, flexural, and tensile strength analysis. The surface texture and failure mechanism of the composites were examined using SEM. The testing results revealed that MF composites had higher tensile and flexural properties than AF and AM composites. However, in terms of impact strength and micro-hardness, AM composites surpassed AF and MF composites. SEM micrographs of MF composites demonstrated greater fiber–matrix bonding, indicating higher thermal degradation resistance in TGA investigations. Rana et al [51] examined the effect of hybridization of the Al and SiC particles reinforced in the hybrid epoxy composites. Tensile and flexural strength decreased as particle loading of aluminium and silicon carbide increased, but impact strength and hardness increased along with the flexural and Young’s modulus. Based on particle loading, the particle-reinforced composite with 50 wt% had the greatest combination of mechanical properties of any produced composite. Thamizhvalavan et al [52] studied an abrasive water jet machining technique to investigate the machinability of aluminium hybrid composites of varied compositions. The results revealed that the percentage rate of B4C with ZrSiO4 ceramic particles has an effect on machinability and surface quality of the Al hybrid composites. Ploughing and cavities on the machined surface of hybrid composites suggest ductile and brittle fracture modes. Yadav et al [53] explored the chemo-mechanical properties of Kevlar fiber/ nano-silica/epoxy hybrid composites. The mixture of SiO2 along with the Kevlar fibers increases hybrid composite mechanical properties by up to 3%. The hardness of hybrid composites (K3) has increased by up to 29% when compared with neat laminates according to Rockwell hardness testing. Tensile strength is nearly increased at 3 wt% nano SiO2 from the neat laminates. The K3’s impact strength has

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increased by 50%. Finally, up to 3 wt% nano SiO2 reinforcement improves the flexural properties as well. Jadeesh et al [54] examined the areca/sisal/carbon-reinforced epoxy hybrid composites made by means of several stacking configurations. Nine distinct laminate combinations were created using the manual hand-layup process. Mechanical characterization results favored the employment of the composites developed in a variety of interior sections of the railways. The morphology of the composites demonstrated proper fiber aggregation in the matrix, resulting in increased mechanical performance. The results of the experiments suggested that the hybridization of natural and synthetic fibers in a polymer matrix could be an appealing potential for use in a variety of interiors designed for rail locomotives. Negi et al [55] used compression molding to evaluate the manufacturing, physicomechanical, and morphological properties of a polypropylene composite reinforced with extracted pine cone scale fiber (NF) and Vigna mungo powder (natural filler). The use of Vigna mungo powder significantly enhanced the flexural and hardness properties. The hybrid composite C2 (30% pine cone scale fiber reinforcement) exhibited the maximum density, tensile strength, and impact strength on account of the chemical treatment of the fibers as it removed the wax covering from the surface of the fiber. Neto et al [56] investigated the influence of UV exposure and spray ageing using water on the mechanical properties of NF and hybrid composites after being treated with MWCNTs. When compared with the unexposed specimens, the hybrid + MWCNT composites increased the Young’s modulus (1000 h) by roughly 7%, flexural modulus (500 h) by 9%, and Young’s modulus (1000 h) by 17% (1000 h). Senel et al [57] investigated the dry sliding wear and friction behavior of graphene/ ZrO2 binary nanoparticles reinforced aluminium hybrid composites. Nonetheless, no studies on the impact of mixed ZrO2 and graphene-reinforced aluminium composites have been done. The tribological characteristics of Al-ZrO2 and Al-ZrO2-graphene composites with variable compositions are studied under varying loads (5 and 10 N). The composite Al – 9% and ZrO2 – 0.15% graphene showed the lowest friction, wear rate, and mass loss.The Table 1 given below provides an elaborative overview on the recent research conducted in characterizing the chemo-mechanical properties of the hybrid composite systems.

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Yashwanth Padarthi, Raghu Raja Pandiyan Kuppusamy

Table 1: Summary of recent research characterizing hybrid composite systems. S.No. Hybrid composite system

Properties analyzed

Ref.

.

Epoxy prepregs with flax and alternating flax/glass-reinforced layers

Tension–tension fatigue loading

[]

.

Carbon fiber (CF), poly(ether-etherketone), and metallic braided wire mesh

Crash worthiness

[]

.

Glass/carbon-epoxy hybrid composites

Pseudo-ductile stress–strain beahvior

[]

.

Epoxy-based hybrid composites

Mechanical properties and burning behavior based on manufacturing processes

[]

.

Hybrid natural fiber (NF)-reinforced polymer composites

Mechanical and thermal properties with the water absorption behavior

[]

.

Plant fiber polymer composites

Crystallinity, interaction between the matrix and fiber, morphology, and behavior of the polymer matrix

[]

.

Polyhedral oligomeric silsesquioxanes (POSS)-based PLA hybrid composites

Mechanical, thermal, rheological, and morphological properties of PLA and PLAbased blends

[]

.

Tobacco stalk flour/magnesium oxysulfate whiskers-reinforced hybrid composites

Mechanical, thermal, and antibacterial properties

[]

.

Carbon fabric‑layered bioepoxy hybrid composites with fillers

Mechanical, thermal, dimensional stability, and morphological performance

[]

.

ZIF-based and graphene oxide composites

Carene vapor sensing

[]

.

Al–AlO–WS hybrid composites

Structural and mechanical properties

[]

.

Boron nitride/spherical aluminum oxide hybrid composites with epoxyorganosiloxane

Thermally conductivity

[]

.

Steel–CF-reinforced plastic (CFRP) hybrid composites

Mode I and Mode II interfacial fracture toughness

[]

.

Hybrid poly(lactic acid) composites

Influence of alkyl ketene dimer on the chemical and thermal properties

[]

.

Manganese oxides/porous carbon (MnxOy @C) hybrid composites

Influence of manganese oxides on the dielectric properties

[]

.

CF-polymer hybrid composites

Thermal transport performance

[]

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15

Table 1 (continued) S.No. Hybrid composite system

Properties analyzed

Ref.

.

Hybrid carbon/ramie fiber epoxy composites

Effect of fiber stacking sequence and orientation on quasi-static indentation properties

[]

.

Novel hybrid composites with epoxy as the matrix

Investigation of weight fraction and alkaline treatment

[]

.

Vetiver grass – red mud-reinforced hybrid Abrasive wear performance composites

.

Indian almond–kenaf fiber-reinforced hybrid composites

Mechanical and biodegradation properties []

.

Hybrid fiber-reinforced composite

Fabrication, machining, and variation in mechanical properties due to hybridization

[]

.

Kevlar and NF-reinforced hybrid composites

Dry sliding wear behavior

[]

.

Aluminum (Al) hybrid nanocomposites reinforced with alumina and graphene oxide

Tribological behavior

[]

.

Carbon nanofiber-based hybrid cementious composites

Reliable sensing of tensile stresses

[]

.

Flax char/CF-reinforced polyamide  hybrid composites

Thermal and mechanical properties

[]

.

Epoxy-based hybrid composites with hexagonal boron nitride and short sisal fiber as reinforcement

High performance microelectronic applications

[]

.

Al/Cup/SiCp/TiCp-based hybrid composites

Microstructure and mechanical properties

[]

.

Al–SiC-graphite hybrid composites

Elastic properties and thermal shock behavior

[]

.

Graphene oxide for D hybrid composites Photothermal effect

[]

.

Alkali-treated moringa/areca-based NF hybrid composites

Physical, mechanical, and morphological properties

[]

.

Epoxy hybrid composites

Morphological and mechanical properties

[]

.

Al/BC/ZrSiO hybrid composites

Abrasive water jet machining

[]

.

Hybrid composites using Kevlar fiber and nano-SiO

Physical and mechanical properties

[]

[]

16

Yashwanth Padarthi, Raghu Raja Pandiyan Kuppusamy

Table 1 (continued) S.No. Hybrid composite system

Properties analyzed

Ref.

.

CF reinforced areca/sisal hybrid composites

Mechanical and morphological properties

[]

.

Pinecone scale fiber/Vigna mungo powder-reinforced polypropylene-based hybrid composites Ripudaman

Physical and mechanical properties

[]

.

MWCNT-based hybrid composites

Effect of ultraviolet radiation and water spraying on the mechanical properties

[]

.

Graphene/ZrO binary nanoparticles reinforced Al hybrid composites

Dry sliding wear and friction behavior

[]

3 Conclusions This review gives recommendations on material selection and defines the criteria on which the selection should be based. This evaluation gives material selection guidelines and highlights that the selection must not be relying only on the fiber stiffness and strength. The chosen matrix and fibers of the hybrid composites must also be attuned in terms of functional, physical, and thermal characterizations and not only based on the properties at the interface. Non-mechanical property characterization has received little attention in the literature despite their enormous potential. New materials, technology, and various advanced designing software have significantly increased the possibilities of manufacturing hybrid composites. Further research is required to have a superior analysis of the underlying mechanisms and to establish design recommendations for usage in industry. Impact is another common argument for employing hybrid composites in the industry, and this issue has garnered a lot of attention in the literature. There has been minimal focus on splintering and integrity of composite structures which are important in many of the stated applications for reasons other than fiber stiffness and strength.

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[33] Yao, Y., Shi, P., Chen, M., Chen, G., Gao, C., Boisse, P., and Zhu, Y., Experimental and numerical study on Mode I and Mode II interfacial fracture toughness of co-cured steel-CFRP hybrid composites, International Journal of Adhesion and Adhesives, 2022, 112, 103030, doi: http://doi:10.1016/j.ijadhadh.2021.103030. [34] Angin, N., Caylak, S., Ertas, M., and Donmez Cavdar, A., Effect of alkyl ketene dimer on chemical and thermal properties of polylactic acid (PLA) hybrid composites, Sustainable Materials and Technologies, ISBN 2243003562. [35] Liu, Y., Liu, X., Xinyu, E., Wang, B., Jia, Z., Chi, Q., and Wu, G., Synthesis of MnxOy@C hybrid composites for optimal electromagnetic wave absorption capacity and wideband absorption, Journal of Materials Science and Technology, 2022, 103, 157–164, doi: http://doi:10.1016/j. jmst.2021.06.034. [36] Hassanzadeh-Aghdam, M. K., Ansari, R., and Deylami, H. M., Influence of graphene nanoplatelets on thermal transport performance of carbon fiber-polymer hybrid composites: Overall assessment of microstructural aspects, International Journal of Thermal Sciences, 2022, 171, 107209, doi: http://doi:10.1016/j.ijthermalsci.2021.107209. [37] Hassan, S. A., Binoj, J. S., Goh, K. L., Mansingh, B. B., Varaprasad, K. C., Yahya, M. Y., Che Othman, F. E., Ahmed, U., Nurhadiyanto, D., Mujiyono, and Wulandari, A. P., Effect of fiber stacking sequence and orientation on quasi- static indentation properties of sustainable hybrid carbon/ramie fiber epoxy composites, Current Research in Green and Sustainable Chemistry, 2022, 5, 100284, doi: http://doi:10.1016/j.crgsc.2022.100284. [38] Rangaraj, R., Sathish, S., Mansadevi, T. L. D., Supriya, R., Surakasi, R., Aravindh, M., Karthick, A., Mohanavel, V., Ravichandran, M., Muhibbullah, M., and Osman, S. M., Investigation of weight fraction and alkaline treatment on catechu linnaeus/hibiscus cannabinus/sansevieria ehrenbergii plant fibers-reinforced epoxy hybrid composites, Advances in Materials Science and Engineering, 2022, 2022, 1–9, doi: http://doi:10.1155/ 2022/4940531. [39] Jena, P. K., Nayak, S., Mohanty, J. R., Samal, P., Mohanty, S. D., Malla, C., Behera, J. R., Khuntia, S. K., and Mohapatra, J., Abrasive wear performance of vetiver grass – red mudreinforced hybrid composites: Effect of fiber loading on various wear properties, Journal of Natural Fibers, 2022, 00, 1–12, doi: http://doi:10.1080/15440478.2021.2018086. [40] Nampoothiri, E. N., Bensam Raj, J., Thanigaivelan, R., and Karuppasamy, R., Experimental investigation on mechanical and biodegradation properties of indian almond–Kenaf fiberreinforced hybrid composites for construction applications, Journal of Natural Fibers, 2022, 19, 292–302, doi: http://doi:10.1080/15440478.2020.1739592. [41] Sharma, K. K., Kushwaha, J., Kumar, K., Singh, H., and Shrivastava, Y., Fabrication and testing of hybrid fibre reinforced composite: A comprehensive review, Australian Journal of Mechanical Engineering, 2022, 00, 1–17, doi: http://doi:10.1080/14484846.2021.2022581. [42] Murali, B., Ramnath, B. M. V., Rajamani, D., Nasr, E. A., Astarita, A., and Mohamed, H., Experimental investigations on dry sliding wear behavior of kevlar and natural fiberreinforced hybrid composites through an RSM–GRA hybrid approach, Materials, 2022, 15, doi: http://doi:10.3390/ma15030749. [43] Mohammed, A. S., Aljebreen, O. S., Hakeem, A. S., Laoui, T., Patel, F., and Ali Baig, M. M., Tribological behavior of aluminum hybrid nanocomposites reinforced with alumina and graphene oxide, Materials, 2022, 15, doi: http://doi:10.3390/ma15030865. [44] Parveen, S., Vilela, B., Lagido, O., Rana, S., and Fangueiro, R., Development of multi-scale carbon nanofiber and nanotube-based cementitious composites for reliable sensing of tensile stresses, Nanomaterials, 2022, 12, doi: http://doi:10.3390/nano12010074.

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[45] Biricik, G. D., Celebi, H., Seyhan, A. T., and Ates, F., Thermal and mechanical properties of flax char/carbon fiber reinforced polyamide 66 hybrid composites, Polymer Composites, 2022, 43, 503–516, doi: http://doi:10.1002/pc.26394. [46] Agrawal, A. and Chandraker, S., An experimental investigation of epoxy-based hybrid composites with hexagonal boron nitride and short sisal fiber as reinforcement for high performance microelectronic applications, Polymer Engineering and Science, 2022, 62, 160–173, doi: http://doi:10.1002/pen.25841. [47] Saha, S., Ghosh, M., Pramanick, A. K., Mondal, C., and Maity, J., Microstructure and mechanical properties of Al/Cup/SiCp/TiCp-based hybrid composites fabricated by spark plasma sintering, Journal of Materials Engineering and Performance, 2022, 31, 424–438, doi: http://doi:10.1007/s11665-021-06164-7. [48] Jana, P., Oza, M. J., Schell, K. G., Bucharsky, E. C., Laha, T., and Roy, S., Study of the elastic properties and thermal shock behavior of Al–SiC-graphite hybrid composites fabricated by spark plasma sintering, Ceramics International, 2022, 48, 5386–5396, doi: http://doi:10. 1016/j.ceramint.2021.11.082. [49] Wang, Q., Zhang, N., Qu, C., Li, S., Guo, L., Yang, Z., Zhang, X., and Wang, T., Photothermal effect of graphene oxide for 3D hybrid composites achieving controllable friction, Tribology International, 2022, 167, 107364, doi: http://doi:10.1016/j.triboint.2021.107364. [50] Nayak, S., Khuntia, S. K., Mohanty, S. D., Mohapatra, J., and Mall, T. K., An experimental study of physical, mechanical and morphological properties of alkali treated moringa/areca based natural fiber hybrid composites, Journal of Natural Fibers, 2022, 19, 630–641, doi: http://doi:10.1080/15440478.2020.1758282. [51] Rana, S., Hasan, M., Sheikh, M. R. K., and Faruqui, A. N., Effects of aluminum and silicon carbide on morphological and mechanical properties of epoxy hybrid composites, Polymers and Polymer Composites, 2022, 30, 096739112110689, doi: http://doi:10.1177/ 09673911211068918. [52] Thamizhvalavan, P., Yuvaraj, N., and Arivazhagan, S., Abrasive water jet machining of Al6063/B4C/ZrSiO4 hybrid composites: A study of machinability and surface characterization analysis, Silicon, 2022, 14, 1093–1121, doi: http://doi:10.1007/s12633-02000888-2. [53] Yadav, P. S., Purohit, R., and Namdev, A., Physical and mechanical properties of hybrid composites using Kevlar fibre and nano-SiO2, Advances in Materials and Processing Technologies, 2022, 00, 1–13, doi: http://doi:10.1080/2374068x.2022.2034312. [54] Jagadeesh, P., Puttegowda, M., Girijappa, Y. G. T., Rangappa, S. M., and Siengchin, S., Carbon fiber reinforced areca/sisal hybrid composites for railway interior applications: Mechanical and morphological properties, Polymer Composites, 2022, 43, 160–172, doi: http://doi:10.1002/pc.26364. [55] Negi, R. S., Prasad, L., Yadav, A., and Winczek, J., Physical and mechanical properties of pinecone scale fiber/vigna mungo powder reinforced polypropylene based hybrid composites, Journal of Natural Fibers, 2022, 00, 1–11, doi: http://doi:10.1080/15440478. 2022.2025983. [56] Neto, J. S. S., de Queiroz, H., Cavalcanti, D., Aguiar, R., Pereira, A., and Banea, M. D., Effect of ultraviolet radiation and water spraying on the mechanical properties of multi-walled carbon nanotubes reinforced natural fiber and hybrid composites, Journal of Applied Polymer Science, 2022, 139, 1–13, doi: http://doi:10.1002/app.51915. [57] Senel, M. C., Dry sliding wear and friction behavior of graphene / ZrO 2 binary nanoparticles reinforced aluminum hybrid composites, 2022, doi: http://doi:10.1007/s13369-022-06661-4.

Part II: Synthesis and characterization

Wanda D. Jones, Bedanga Sapkota, Shaik Jeelani, Tarig A. Hassan, Melissa Hines, Vinod Dhanak, Vijaya K. Rangari

Synthesis and characterization of carbon nanotube/polyhedral oligomeric silsesquioxane hybrid nanocomposites Abstract: In this study, multiwalled carbon nanotubes (CNTs) coated with functionalized polyhedral oligomeric silsesquioxanes (POSS) were studied as potential polymer fillers. A straightforward sonochemical method is used to coat CNTs with four different types of POSS® functionalized materials: (a) glycidylethyl (GE)-POSS, (b) octaIsobutyl (OI)-POSS, (c) epoxycyclohexyl (EC)-POSS, and (d) glycidylisooctyl (GI)-POSS. Surface coating of CNTs with POSS was analyzed using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The FTIR results indicated that the epoxy rings may be open and attached to the surface of CNTs in case of EC-POSS. XPS results show the decrease of carbon upon coating of POSS as compared to the pristine CNTs. The percentage of decrease in carbon atom upon coating is ~−6%, −12%, and −18% for OI-POSS, GI-POSS, and GE-POSS, respectively. TGA analyses show the ~75 wt%, 50 wt%, and 23 wt% coverage of GE-POSS, EC-POSS, and GI-POSS on CNTs, respectively. HRTEM confirms the uniform coating of the POSS on CNTs. These various types of coatings of POSS on CNTs can be used as potential polymer fillers for lightweight high-strength polymer nanocomposite. Keywords: CNTs, POSS, sonochemical coatings, characterization, spectroscopy, microscopy

Acknowledgments: The authors thank the NSF-PREM# 0611612, #1827690, Alabama EPSCoR, 1655280, NSF-RISE #1459007, and Alabama Commission on Higher Education for financial support. Wanda D. Jones, School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853 Bedanga Sapkota, Shaik Jeelani, Tarig A. Hassan, Department of Materials Science and Engineering, Tuskegee University Tuskegee, AL 36088 Melissa Hines, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853 Vinod Dhanak, Physics Department, University of Liverpool, Liverpool L69 3BX, UK Vijaya K. Rangari, Department of Materials Science and Engineering, Tuskegee University Tuskegee, AL 36088, e-mail: [email protected] https://doi.org/10.1515/9783110724684-002

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1 Introduction Carbon nanotubes (CNTs) have been become the central of interest among researcher in various fields including chemistry, physics, materials science, and engineering since its discovery in 1991 [1]. CNTs are viewed as a sheet of graphene rolled into a tube, which can exist either in single-walled or multi-walled arrangements. Multi-walled CNTs are formed by concentric single-walled CNTs (SWCNTs). CNTs have exceptional material properties, including superior thermal stability, thermal conductivity, and electric current carrying capacity. They can be synthesized using a number of techniques, such as arc discharge, laser ablation, and chemical vapor deposition [2–4]. For these reasons, broad research work has been conducted to understand the fundamentals of this material as well as to develop CNT hybrid nanocomposites for multifunctional applications [5–9]. Research studies have demonstrated that incorporation of CNTs into polymer can improve the physical, mechanical, thermal, and chemical properties and, subsequently, the overall performance of polymer. A number of research have studied the nanotubes as reinforcements in polymer composites using thermoplastic matrices [10–15]. Vivekchard et al. observed significant improvements in composite strength after adding SWCNTs to polypropylene (PP) by solution processing [16]. They reported that even at 1 wt% loading, the tensile strength and modulus were 40% and 55% higher, respectively, than neat PP fibers. Another group reported a 25% increase in tensile stress of polystyrene by the addition of only 1 wt% CNTs [17]. Safadi et al. reported that the strength of PS/multi-walled CNT (MWCNT) composites increased by 40% when less than 1 vol% of nanotubes were added [18]. Other researchers also reported significant increase in the stiffness of MWCNT/PMMA composites at high temperatures, depending on the loading of CNTs [19]. Epoxies have been widely used as thermosetting matrices for CNT reinforcement [20–23]. The performance of a nanocomposite is affected by the degree of integration of nanoparticles with the host polymer [24]. Optimization of composite components and their interaction can result in improvements in mechanical, optical, and electrical properties. Characteristically, CNTs are inert and do not react with many matrices, resulting in poor dispersion. Thus, researchers have used different techniques to increase dispersion, including functionalization of CNTs. Gong et al. studied surfactants as wetting agents to facilitate the dispersion of CNTs where improvements in both the mechanical and thermal properties of CNT-epoxy composites were reported [20]. Zhu et al. studied a combination of acid treatment and fluorination method to improve dispersion of SWCNTs in an epoxy matrix [22], which resulted in a more efficient interaction with the matrix and an overall enhancement in mechanical properties (29% increase in tensile modulus and 14% increase in tensile strength). Tiano et al. reported functionalized nanotubes for the construction of epoxy composite, which resulted in an 11% increase in stress and a 21% increase in modulus with 1 wt% load of CNTs in epoxy [21]. Wang et al. reported improvement in the storage modulus of matrix by 25% upon 0.5% wt loading of the amino-functionalized nanotubes in epoxy [17].

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A category of nanofillers that has had an impact on epoxy resin systems are the polyhedral oligermic silsesquioxanes (POSS). POSS nanofillers have been used in various polymeric systems, resulting in improvements in overall properties including toughness, hardness, and corrosion and fire resistance [25, 26]. Unlike CNTs, POSS nanofiller modified with certain functional groups can be covalently bonded with the polymer matrix [27–29]. Functionalization of POSS molecules can be performed to alter surface reactivities, which can promote interactions and compatibility with the polymers [30–36]. If functionalized POSS is used with inert CNTs, it is expected that CNTs dispersion in polymer matrix can be improved. Chen and Shimizu have grafted CNTs with POSS and dispersed these composites in a poly(L-lactide) matrix. They observed strong interfacial adhesion between the nanotubes and the matrix by microscopy [36]. Zhang and coworkers covalently linked aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS–NH2) with the MWCNTs with surface-bonded acyl chloride moieties (MWCNT–COOH) to prepare soluble composite material MWCNT/ POSS. This composite material showed a noteworthy optical limiting performance for nanosecond laser pulses at 532 nm [37]. Wu and coworkers incorporated buckypaper from CNTs onto the surface of a POSS/glass fiber composite by vacuum-assisted resin transfer-molding technique to improve the flame retardency. The Bucky-paper assisted in reducing several factors during combustion that included the heat release rate, peak heat release rate, and smoke production rate [38]. In this work, we have studied the sonochemical coating of four types of POSS on CNTs to produce a hybrid nanocomposite, which may be suitable for fabrication of high-strength CNTs/POSS nanocomposites for structural applications.

2 Experimental 2.1 Materials Glycidylethyl (GE)-POSS, octaisobutyl (OI)-POSS, epoxycyclohexyl (EC)-POSS, and glycidylisooctyl (GI)-POSS (OI-POSS, EC-POSS, GE-POSS, and GI-POSS) were purchased from Hybrid Plastics Inc. (USA). The solvent n-hexane was purchased from Sigma-Aldrich Chemicals, USA. Multiwalled carbon nanotubes (CNTs 10–20 nm in diameter and 0.5–20.0 µm in length) were purchased from Nanostructured & Amorphous Materials, Inc., and were synthesized by chemical vapor deposition.

2.2 Sonochemical coating of POSS nanofillers on CNTs One gram of each POSS nanofiller (GE-POSS, OI-POSS, EC-POSS, and GI-POSS) and one gram of CNTs were mixed in 70 mL of n-hexane and irradiated with a high-

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intensity ultrasonic horn for 3 h at 5 °C. The reaction product was thoroughly washed with DI water and then with ethanol. These products were centrifuged after each wash at 10,000 rpm and vacuum-dried overnight at room temperature [39]. The as-prepared materials were characterized using TEM, TGA, FTIR, and XPS.

2.3 Morphological studies Morphological observations were made by transmission electron microscopy (TEM) to study the extent of POSS coating on CNTs. The TEM characterization was carried out using a JEOL-2010 high-resolution TEM at 200 kV. The samples for high-resolution TEM were prepared by dispersing various MWCNTs nanoparticles in ethanol. A drop of dispersion was placed on a copper grid (copper grid-200 mesh) which was air-dried and then used for HR–TEM analysis.

2.4 Thermal studies Thermogravimetric analysis (TGA) was performed to understand the thermal stability of POSS-coated CNTs. A Mettler Toledo TGA/SDTA 851e apparatus under nitrogen and oxygen atmospheres was used. TGA samples ranged in weight between 10 and 15 mg. Samples were kept in an alumina sample crucible, weighed, and heated to 800 °C from room temperature at a heating rate of 10 °C/min. Real-time material characteristic curves were generated by a Mettler data acquisition system. The initial weight loss at 5 wt%, denoted as Td5%, was obtained. The decomposition temperature, denoted as Tdec, which is the major weight loss observed, was obtained. The thermal residue at 800 °C, denoted as ΔW, was also obtained.

2.5 Chemical studies XPS was conducted to analyze the chemical composition of POSS-coated CNTs. Plots of the number of electrons detected against the binding energy (B.E.) of the electrons detected were obtained to produce XPS peaks at characteristic B.E. values. XPS characterization was performed with a PHI 5700 ESCA system possessing a scan step size of 0.5 eV. Atomic percentages were obtained from elemental survey scans and reported relative to the total signals for carbon, oxygen, and silicon. FTIR was performed to detect organic and inorganic materials in the POSScoated CNTs. FTIR measurements were carried out in transmission mode using a Nicolet spectrometer equipped with a Pike Technologies attenuated total reflectance. The spectra were collected with a Germanium crystal using 64 scans with a 4 cm−1 resolution step.

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3 Results and discussion 3.1 Characterization of CNTs by TEM TEM studies were performed to understand the deposition of POSS coating on CNTs. Figure 1a shows the TEM image of the as-received CNTs. The diameter of the CNTs is in the range between 10 and 20 nm. The as-received CNTs were wellseparated with minimal agglomeration.

Figure 1a: TEM micrographs of pristine CNTs at low resolution (left image) and high resolution (right image).

Figure 1b represents the TEM micrographs of OI-POSS nanofiller-coated CNTs. The micrograph clearly shows coverage of the OI-POSS particles on the CNTs; however, the concentration of coating is very minimal. The poor coverage may be due to the fact that the OI-POSS are held onto the CNTs surface by weak Van der Waals forces which can be easily separated. This is indicated by the changes in the lattice as seen in high magnification image. Figure 1c represents the TEM micrographs of EC-POSS nanofiller-coated CNTs. The changes in the lattices as seen in high magnification image clearly show that the particles are on the surface of the CNTs. By using sonication, the particles anchored to the CNTs. The possible reasons for this may be the degree of compatibility of EC-POSS with CNTs. Figure 1d represents the TEM micrograph of GE-POSS nanofiller-coated CNTs. The micrograph clearly shows that the particles were well-coated over the CNTs, and the extent of coating was sufficient to cover most of the CNTs. High magnification micrographs clearly show a higher degree of coverage of GE-POSS particles over the CNTs compared to OI-POSS and the EC-POSS-coated CNTs. The possible reasons for this may be the degree of compatibility of GE-POSS with CNTs.

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Figure 1b: TEM micrographs of OI-POSS/CNTs at low and high magnification.

Figure 1c: TEM micrographs of EC-POSS/CNTs at low and high magnification.

Figure 1d: TEM micrographs of GE-POSS/CNTs at low and high magnification.

Synthesis and characterization of carbon nanotube/polyhedral

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Figure 1e represents the TEM micrograph of GI-POSS nanofiller-coated CNTs. The micrograph clearly shows a much higher concentration of the GI-POSS coating on the CNTs compared to the previous samples. High magnification micrographs clearly show even distribution and good coverage of GI-POSS particles on CNTs. The possible reasons for this may be the compatibility of GI-POSS with CNTs.

Figure 1e: TEM micrographs of GI-POSS/CNTs under low and high magnification.

3.2 TGA analysis of pristine and POSS-coated CNTs TGA was carried out to estimate the percentages of various POSS coatings on CNTs. All these results are summarized in Table 1. Figure 2a–d depicts the representative TGA graphs for pristine CNTs and EC POSS-coated CNTs in nitrogen and oxygen atmospheres, respectively. Figure 2a shows that the initial weight lost at 5 wt% (Td5%) was observed at 667 °C, and the decomposition temperature (Tdec) was observed at 676 °C. The thermal residue at 800 °C (ΔW) is ~77 wt%. Figure 2b shows that the weight losses occurred at lower temperatures (540 and 620 °C) than the samples tested under nitrogen atmosphere, and the ΔW is ~10 wt%. These results suggest Table 1: Thermal and thermal oxidative stability values for pristine and POSS-coated CNTs. CNTs

Pristine CNTs OI-POSS/CNTs EC-POSS/CNTs GE-POSS/CNTs GI-POSS/CNTs

Td% (°C)

Tdec (°C)

Nitrogen

Oxygen

Nitrogen

Oxygen

    

    

 ,  ,  ,  , 

 ,  ,  ,  , 

ΔW (% at  °C) Nitrogen

Oxygen

    

    

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85

–0.00015 –0.00020

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0.0001

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–0.0003 70

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Temperature (oC)

Figure 2: TGA micrographs for (a) pristine CNTs in nitrogen atmosphere; (b) pristine CNTs in oxygen atmosphere; (c) EC POSS-coated CNTs in nitrogen atmosphere, and (d) EC POSS-coated CNTs in oxygen atmosphere.

Derivative Weight Loss (1/C)

–0.0001

c

100

Weight Loss (%)

0.0000

Temperature (oC)

Weight Loss Derivative (1/C)

0.000

100

Weight Loss (%)

–0.0025

0

Temperature (oC)

90

–0.0020

Oxidative Stability

–0.00025

Weight Loss Derivative (1/C)

a

0.0000

Weight Loss (%)

90

0.00000

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Weight Loss (%)

95

Derivative Weight Loss (1/C)

0.00005

30

0.0005

0.00010 100

Synthesis and characterization of carbon nanotube/polyhedral

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that the decomposition of CNTs in the presence of oxygen is rapid. The decomposition of CNTs in the presence of oxygen is observed at ~90 wt% compared to 77 wt% in case of nitrogen. As summarized in Table 1, it can be concluded that the sonochemically coated POSS nanofillers on CNTs decompose at higher temperatures compared to the as-received POSS nanofillers. The reason for this is may be due to the covalent bonding of POSS onto the CNTs. The TGA results were also used to estimate the amount of POSS coating on the CNTs using the thermal residues of the samples tested under both the nitrogen and oxygen atmospheres as reported in the literature [40, 41]. Based on these results, it was found that coverage of the OI-POSS and GE-POSS on the CNTs surface was approximately 75%. Coverage of the EC-POSS and GI-POSS on the CNTs was approximately 50% and 23%, respectively. During the actual sonication process, a 1:1 ratio of POSS nanofillers to CNTs was used. These differences in the amount of POSS coatings on the CNTs can be attributed to density variations and the sonication process breaking down the structure of the POSS nanofillers.

3.3 Fourier transform infrared spectroscopy FTIR was conducted to detect the functional groups that are attached at the surface or the sidewalls of the CNTs. Figure 3a–e shows FTIR spectra for all POSScoated CNTs. In the FTIR spectra, the most important region of the coated CNTs is the fingerprint region, which ranges from 1200 cm−1 to 600 cm−1 [42]. This region is crucial to understand small differences in the structure and constitution of a molecule upon coating process [42]. Other major changes can also be observed in the lower group frequency regions. Major peaks for the pristine CNTs were observed at wave numbers 720 cm−1, 783 cm−1, and 865 cm−1. Typical FTIR spectra of POSS nanofillers indicate that the cage structure of Si–O–Si lies between wave numbers 1030 and 1110 cm−1 , which can be compared to that observed for POSS-coated CNTs [34]. Other groups present in that region originate from the main functional groups present on the cage structure. For both OIPOSS and OI-POSS/CNTs, the major peaks were similar. Comparatively, for ECPOSS and EC-POSS/CNTs, a stretching vibration band shift was observed for the Si–O–Si cage in the 1112 cm−1–1099 cm−1 region, which was assigned to the rupture of the cage structure. Generally, epoxy ring symmetric vibrations will be observed at 745 cm−1. However, the asymmetric vibrations of glycidyl epoxy rings in GE-POSS or GI-POSS-coated CNTs were observed between 810 and 950 cm−1. Table 2 lists the main functional groups apparent in the POSS and the POSS/ CNTs.

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Table 2: Characteristic absorption band of epoxy and siloxane functional groups. Wavenumber (cm−)

Vibration type

– – – 

νs δs νs νs

O

–

νas

O

–

νs,  μ-band

O

–

νs

Functional Group Si–O–Si Si–H C=C O

CH in

where υs, υas, and δs are symmetric vibration, asymmetric vibration, and inplane bending, respectively. Table 3 lists the peaks observed from the FTIR spectra. OI-POSS and OI-POSS/CNTs peaks remained the same. When the CNTs were coated with EC-POSS, several peaks disappeared, and new peaks appeared along with a shift in the Si–O–Si cage. Other shifts of 5 cm−1 or less also occurred in the lower group frequency region, accounted for by the epoxy ring CH group. This shift was another indication that EC-POSS on the CNT surface was reactive to some degree. For GE-POSS, two peaks disappeared or shifted. Other reactivity was detected in GI-POSS and in the coated CNT counterpart. Peaks 875 and 930 cm−1 disappeared, but the CH groups in the epoxy exhibited major shifts in the region between 2865 and 2978 cm−1. This reactivity suggests that the epoxy rings may be opening and attaching to the surface of the CNTs. The main functional groups were apparent in the POSS and POSS/CNTs. In Table 3, peak shifts are highlighted with bold, and the peak appearance or disappearance is shown in parentheses. From these results, it can be determined that the surface of the CNTs contained the desired functional groups.

3.4 X-ray photo-electron spectroscopy (XPS) XPS is a surface chemical analysis technique that can be used to analyze the chemical composition of a material in its “as received” state or upon various treatments such as coating or functionalization of the CNTs. These characteristic peaks represent the arrangement of the electrons within the atoms, for example, 1s, 2s, 2p, and 3s. XPS spectra of binding energies for coated CNTs are shown in Figure 4. In order to find the atomic percentage, each raw XPS signal was corrected by dividing its signal intensity by a “relative sensitivity factor” and then normalizing over all of the elements detected. XPS characterization of these materials was undertaken via analysis of the elemental composition of the surface

800 1000 1200 1400 1600 1800

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Absorbance

Absorbance

(b) OI-POSS/CNTs

80 0

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Absorbance

Absorbance

(d) GE-POSS/CNTs

800

800 1000 1200 1400 1600 1800

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Wave Number (cm-1)

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Wave Number (cm-1)

(e) GI-POSSCNTs

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(c) EC-POSS/CNTs

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Wave Number (cm-1)

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Synthesis and characterization of carbon nanotube/polyhedral

Figure 3(a–e): FTIR spectra of (a) pristine CNTs, (b) OI-POSS/CNTs, (c) EC-POSS/CNTs, (d) GE-POSS/CNTs, and (e) GI-POSS/CNTs.

(a) Pristine CNTs

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Table 3: Peak positions observed for FTIR. Wavenumber (cm−) OI-POSS             

OI-POSS/ CNTs

EC-POSS

EC-POSS/ CNTs

GE-POSS

GE-POSS/ CNTs

GI-POSS

GI-POSS/ CNTs

            

()        ()        () ()  

  ()     ()    ()  ()       

   () ()      

         

   () ()    () ()   

    ()     

Table 4: Binding energy for the pristine and POSS-coated CNTs. Sample

Pristine CNTs Octa isobutyl POSS/CNTs

POSS empirical formula

SiO (CH) Epoxy cyclohexyl POSS/CNTs SiO (CHCHCHO) Glycidyl ethyl POSS/CNTs SiO (CH) (CH)OCHCHCHO Glycidyl isooctyl POSS/CNTs SiO (CH)OCHCHCHO (CH(CH)(CH)CH)

XPS measured composition At%

XPS-binding energies (eV) indicates BE reference

Si

O

C

Cs

Os

Sip

. .

. .

. . . . . . . .

.

.

. . . .

.

.

. . . .

.

.

. . . .

OI POSS CNTs

EC POSS CNTs 25000

40000

a

50000

c

b

35000

20000

30000 25000

20000

15000

20000

CPS

CPS

30000

15000

10000

10000 5000 5000

10000 0 0

0

-5000 1000

800

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400

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Binding Energy (eV)

800

600

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0

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GI POSS CNTs

GE POSS CNTs 35000 200

e

d 30000

150

25000 20000

100

50

15000 10000 5000

0

600

400

Binding Energy (eV)

Binding Energy (eV)

CPS

1200

CPS

CPS

40000

200

0

Synthesis and characterization of carbon nanotube/polyhedral

Figure 4(a–e): XPS spectra of binding energies for the (a) pristine CNTs, (b) OI-POSS CNTs, (c) EC-POSS CNTs, (d) GE-POSS CNTs, and (e) GI-POSS CNTs.

Pristine CNTs 60000

0 1200

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200

0

35

Binding Energy (eV)

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a

O s1 overlay (Oxygen) N e a t C N Ts O I P O S S C N Ts E C P O S S C N Ts G E P O S S C N Ts G I P O S S C N Ts

6000 5000

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b Wanda D. Jones et al.

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C s1 overlay (Carbon) N e a t C N Ts O I PO SS CNTs EC PO SS CNTs G E PO SS CNTs G I PO SS CNTs

CPS

40000

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3000 2000

10000 0 300

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295

290

285

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0 550

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S iO s1 overlay (Si) N e a t C N Ts O I P O S S C N Ts E C P O S S C N Ts G E P O S S C N Ts G I P O S S C N Ts

c

400 300 200 100 0 115

535

530

Binding Energy (eV)

Binding Energy (eV)

CPS

Figure 5(a–c): XPS overlay of the (a) C1s, (b) O1s, and (c) Si2p-binding energies for neat CNT and upon coating with POSS nanofillers.

7000

50000

110

105

100

Binding Energy (eV)

95

525

520

Synthesis and characterization of carbon nanotube/polyhedral

37

region and the binding energy. XPS overlay of C1s, O1s, and Si2p-binding energies for coated CNTs is shown in Figure 5. Analysis of the Si and O regions was also performed to confirm attachment to the CNT surface. Oxygen (O1s), silicon (Si2p), and carbon (C1s) elements are found at binding energies of 532.0, 102.8, and 284.6, respectively. From the data, we observed decreases in the atomic percentage of carbon on the coated CNTs compared to the pristine CNTs. Table 4 lists atomic percentages, showing decreases in atomic percentage of carbon for OI-POSS, GI-POSS, and GE-POSS of −6%, −12%, and −18%, respectively. Atomic percentages of oxygen and silicon increased by 500% and above. EC-POSS-coated CNTs exhibited the lowest decrease in carbon at −20% and the highest increase in silicon and oxygen on the surface. These results are in agreement with the FTIR spectral results.

4 Conclusions In this work, sonochemical method was effectively used for coating functionalizedPOSS nanofillers onto CNTs. The maximum coating (75%) was observed for OIPOSS and GE-POSS nanofillers. Thermal analysis results indicated that there was an increase in thermal stability of POSS upon the incorporation of CNTs. Highresolution FTIR and XPS both indicated that POSS molecules were present on the CNT surface after the coating process. Overall, this work showed that functionalized POSS-infused CNTs nanocomposites can be easily and effectively produced. These hybrid nanocomposites have high potential to be used as polymer fillers to modify thermoplastic and thermoset polymeric materials for lightweight and high strength automotive and aerospace application.

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[25] Franchini, E., Galy, J., Gerard, J. F., Tabuani, D., and Medici, A., Influence of POSS structure on the fire retardant properties of epoxy hybrid networks, Polymer Degradation and Stability, 2009, 4, 1728–1736. [26] Gao, L., Zhang, Q., Zhu, M., Zhang, X., Sui, G., and Yang, X., Polyhedral oligomeric silsesquioxane modified carbon nanotube hybrid material with a bump structure via polydopamine transition layer, Materials Letters, 2016, 183, 207–210. [27] Yen, Y.-C., Kuo, S.-W., Huang, C.-F., Chen, J.-K., and Chang, F.-C., Miscibility and hydrogen-bonding behavior in organic/inorganic polymer hybrids containing octaphenol polyhedral oligomeric silsesquioxane, The Journal of Physical Chemistry B, 2008, 112, 10821–10829. [28] Yadav, S. K., Mahapatra, S. S., Yoo, H. J., and Cho, J. W., Synthesis of multi-walled carbon nanotube/polyhedral oligomeric silsesquioxane nanohybrid by utilizing click chemistry, Nanoscale Research Letters, 2011, 6, 122. [29] Du, W., Shan, J., Wu, Y., Xu, R., and Yu, D., Preparation and characterization of polybenzoxazine/trisilanol polyhedral oligomeric silsesquioxanes composites, Materials and Design, 2010, 31, 1720–1725. [30] Ni, C., Ni, G., Zhang, S., Liu, X., Chen, M., and Liu, L., The preparation of inorganic/organic hybrid nanomaterials containing silsesquioxane and its reinforcement for an epoxy resin network, Colloid and Polymer Science, 2010, 288, 469–477. [31] Zhang, Z., Gu, A., Liang, G., Ren, P., Xie, J., and Wang, X., Thermo-oxygen mechanisms of POSS/epoxy nanocomposites, Polymer Degradation and Stability, 2009, 92, 1986–1993. [32] Qiu, Z. and Pan, H., Preparation, crystallization and hydrolytic degradation of biodegradable poly(L-lactide)/polyhedral oligomeric silsesquioxanes nanocomposites, Composites Science and Technology, 2010, 70, 1089–1094. [33] Su, C. H., Chiu, Y. P., Teng, C. C., and Chiang, C. L., Preparation, characterization and thermal properties of organic–inorganic composites involving epoxy and polyhedral oligomeric silsesquioxane (POSS), Journal of Polymer Research, 2010, 17, 673–681. [34] Ramírez, C., Rico, M., Torres, A., Barral, L., López, J., and Montero, B., Epoxy/POSS organic– inorganic hybrids: ATR-FTIR and DSC studies, European Polymer Journal, 2008, 44, 3035–3045. [35] Chen, G. X. and Shimizu, H., Multiwalled carbon nanotubes grafted with polyhedral oligomeric silsesquioxane and its dispersion in poly(L-lactide) matrix, Polymer, 2008, 49, 943–951. [36] De Farias, M. A., Coelho, L. A. F., and Pezzin, S. H., Hybrid nanocomposites based on epoxy/ silsesquioxanes matrices reinforced with multi-walled carbon nanotubes, Materials Research, 2015, 18(6), 1304–1312. [37] Zhang, B., Chen, Y., Wang, J., Blau, W. J., Zhuang, X., and He, N., Multi-walled carbon nanotubes covalently functionalized with polyhedral oligomeric silsesquioxanes for optical limiting, Carbon, 2010, 48, 1738–1742. [38] Wu, Q., Zhang, C., Liang, R., and Wang, B., Fire retardancy of a buckypaper membrane, Carbon, 2008, 46, 1159–1174. [39] Jones, W. D., Rangari, V. K., Hussan, T. A., and Jeelani, S., Synthesis and characterization of (FE3O4/MWCNTs)/epoxy nanocomposites, Journal of Applied Polymer Science, 2010, 16, 2783–2792. [40] Mansfield, E., Tyner, K. M., Poling, C. M., and Blacklock, J. L., Determination of nanoparticle surface coatings and nanoparticle purity using microscale thermogravimetric analysis, Analytical Chemistry, 2014, 86(3), 1478–1484.

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Part III: Applications and analysis

Padmanabhan Krishnan

Viscoelastic response of hybrid polymeric dental composites in sliding contacts and applications Abstract: The viscoelastic response of polymeric solids to sliding contact conditions is observed and analyzed with respect to the sliding speed, material composition, and geometry. It was discovered that polymeric solids produced their own distinct viscoelastic signatures that cause resonance at certain sliding speeds which can be explained with resonance conditions for electromagnetic waves. The observed viscolelastic phenomenon is characterized with respect to the relaxation and recovery times for rigid polymeric solids. It is confirmatory as a demonstration of proof of existence of viscoelasticity and self-organization in these materials under sliding contact conditions. Viscoelastic observations are also made on the aged specimens in sliding contact. Keywords: Viscoelasticity, polymer, hybrid composites, surfaces, sliding contact, ageing, stress waves

1 Introduction Polymer-based composites with ceramic fillers are being increasingly used in dental applications as they combine the requirements for strength, fatigue, toughness, and bio-compatibility with enamel and wear resistance. The surface integrity and long-term wear performance of these materials is a key issue in deciding their suitability for dental applications. Pin on disc (POD) sliding wear testing of dental restorative materials (amalgam, ceramics, polymers, and composites) is a widely accepted practice to generate data and evaluate the contact wear performance of these materials prior to other wear test methods approved for use in dentistry. During the POD sliding wear of polymeric composites at loads ranging from a moderate contact load of 5 N to a load of 15 N corresponding to the occlusal forces on the molars, the choice of low sliding speeds of 2–5 mm/s was seen to produce some interesting and periodic distortions in the friction force trace that can be mistaken

Acknowledgement: The author thanks VIT management and the School of Mechanical Engineering colleagues for the wonderful support and encouragement. Padmanabhan Krishnan, School of Mechanical Engineering, Vellore Institute of Technology, Vellore 632014, India, e-mail: [email protected] https://doi.org/10.1515/9783110724684-003

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Padmanabhan Krishnan

for machine-related vibrations to begin with and considered undesirable in the measurement of frictional force and estimation of the coefficient of friction. This new disruptive discovery was later proven to be viscoelastic in nature as the machine vibrational frequencies were higher by an order or more. The discovery of such a viscoelastic response would lead to many important applications later.

2 Viscoelastic models and the phenomena In plastic materials, prolonged exposure to stress may cause noticeable and irreversible deformation which must be taken into consideration when designing parts for structural and bio-medical applications. The susceptibility to permanently deform under load or a relaxation mechanism under stress can be measured in creep and stress relaxation experiments, respectively [1–4]. In the simplest case, the relaxation mechanism under a constant strain can be described with the help of onedimensional Maxwell model which consists of a spring and dashpot in series.

Figure 1: The Voigt and Maxwell viscoelastic models.

According to the model shown in Figure 1, an instantaneous strain causes only the elastic spring to initially deform, while the viscous dashpot slowly and gradually relaxes and allows the spring to slowly return to the original condition. Thus, for times much shorter than the relaxation time, the Maxwell element behaves essentially like a spring, whereas for times much longer than the relaxation time, it behaves like a dashpot [5].

Viscoelastic response of hybrid polymeric dental composites

45

An ideal linear elastic material does not experience any relaxation process. This material can also be described with the Voigt model which consists of a spring parallel to a dash pot. In this arrangement, no relaxation takes place because the viscoelastic flow is restricted by the spring element. The viscoelastic behavior of real polymeric materials is much more complicated, that is, these materials neither fully relax nor are they ideally elastic. To accurately describe their relaxation behavior, Maxwell and Voigt elements have to be combined with more complex arrangements. Zener arrangements and models are also exhibited by polymers that show a linear viscoelastic behavior which explains the creep and stress relaxation phenomena [6]. Zener models normally consist of Maxwell Kelvin–Voigt models in series or parallel arrangements. Burger materials are examples of a set of polymers obeying the viscoelastic models with the Maxwell material and Kelvin material in series [6]. To study this strange phenomenon in sliding contacts further, parameters like geometry (human enamel pin on polymeric disc or an alumina ball with a wider contact area on disc) and material microstructure of the pin as well as the disc {polymer-ceramic filler, ceramic filler-polymer-binder, and ceramic-(glassy)ceramic composites} were considered, and combinations of geometry and material systems were tried out to study the phenomenon further in a quantitative and methodical manner. The wear behavior of these materials was also studied using a POD apparatus and the results, presented.

3 Experimental procedures The two composites used in this study were Hybrid Composite 1: A methacrylic ester matrix with silanated barium alumina silica glass and silicon dioxide microfillers by 70 wt% with an average particle size of 1 μm. Hybrid Composite 2: A hybrid ceramic composite (enamel and dentin) with 92 wt% of fine glass (0.1–10 μm, average 2 μm, and microfiller < 0.1 μm). The resin being bis–glassy methacrylate (bis–GMA) and triethylene glycol methacrylate (TEGMA). Composite restorative discs of approximately 15 mm diameter and 3 mm thickness were prepared by light curing the samples between glass plates with inner Mylar™ film sheets (a thermoplastic-added polyester) and circular (polytetrafluoroethylene) dams of 3 mm thickness in order to obtain uniformly cured discs. The curing was for a time period between 60 and 120 s using a xenon light source with a strobe mode (Dentacolor XS, Heraeus Kulzer) based on manufacturer’s recommendations for individual pastes of raw materials in tubes. The fabricated discs were dry-polished using grit 600 abrasive paper which is the normal grit size used for restorative finishes and

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Padmanabhan Krishnan

finished with “Texmet” cloth to a maximum surface roughness of Rmax ~ 2.5 to 3.5 μm and an average roughness of Ra = 0.257 µm. Another set of discs were dry-polished to a surface roughness of Rmax ~ 0.9–1.5 μm using grit 1200 and “velvet” cloth to obtain a surface smoother than the average particle size down to about an Ra of 0.15 µm. Acetone was used in minimum quantities to clean the surfaces that were dried and then electric-blower-dried. Machined and polished human enamel pins from third maxillary molars and pins of the polymeric materials that constitute the disc were used, with a maximum possible tip roughness of 0.2 μm. Alumina balls (8.02 mm diameter) with an average surface roughness Ra of 0.1 μm were also considered as pin materials, but these were used as received. Needless to say, the contact area of the balls with the disc can be expected to be higher than the pins but Hertzian likewise. Thus, the counterfaces were defined. Sliding contact tests were conducted at 1–15 mm/s sliding speeds in a POD. A schematic sketch of the sinusoidal stress waves produced at different revolutions per minute (rpm) is presented in Figure 2.

Figure 2: A schematic sketch of the sinusoidal stress waves produced at different rpm.

This sketch also explains how viscoelastic signals lead to resonance when the wear track perimeter and the wavelength of a single signal match under specific ratios. Friction force traces were obtained at various rpm. Some pins and discs were conditioned

Viscoelastic response of hybrid polymeric dental composites

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in distilled water at room temperature up to absorption saturation to obtain consistent wear data on distilled water-conditioned specimens and compare them with dry wear data. This process required that specimens be stored for any time between 3 days and 2 weeks until the sample weight was steady correct to 0.1 mg. Certain select specimens were aged for longer durations of up to 8 months and then wear-tested to evaluate the long-term effects on wear of these composites. This replicates the oral environment. The current investigation is a step further that reports a discovery that can aid in characterizing the mechanical properties of polymers and their composites by sliding contact tests and explains the phenomenon with examples. Ageing of the samples has also been investigated.

4 Results and discussion During the POD sliding wear of polymer-based composites using a CSEM tribometer (Geneva, Switzerland) at a load range of 5–15 N corresponding to moderate chewing to occlusal forces in the mouth, in dry and distilled water conditioned environment, the choice of the conventionally adopted low sliding speeds of 0–15 mm/s was seen to produce some interesting and periodic but secondary distortions, rendering the measurement of friction force and hence the determination of coefficient of friction unreliable. Such an observation and analysis seems to have missed the attention of others who have reported the mean coefficient of friction and related wear data on such composites under similar conditions. As the sliding speed is increased to 15 mm/s for wear track radii in the range of 4–5 mm, i.e. from ~ 10 rpm to 40 rpm for the disc dimensions in this study, low speed periodic, localized wave packets were observed as in Figures 3–6, if the material is a polymer or its composite viz. Composites 1 and 2. This was observed for any pin/ball geometry or material like its own counterface, enamel, or alumina. To negate any influence of smoothening effects due to “wearing in,” the experiment was conducted by decreasing the sliding speed from 40 rpm to 10 rpm. Low speed distortions were still observed with the same amplitude. Here, Series 1 refers to Composite 1 and Series 2 refers to Composite 2. It was also seen that the amplitude of the wave like distortion was proportional to the polymer matrix content in the disc material. For example, Composite 1 which contains 30 wt% of methacrylic ester, a polymer, exhibited a higher amplitude of wave like signature than Composite 2 which contains only 8 wt% of polymer, a blend of bis-GMA/TEGMA (see Figure 2). The low rpm coefficient of friction varies by ~ ±10% at maxima in case of Composite 1 against alumina ball in dry conditions. The same composite exhibited an amplitude variation of up to ±75% at maxima with the human enamel as the pin material in the same conditions. Composite 1 disc with Composite 1 pin yielded wave packets similar in amplitude to those with the enamel

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Figure 3: Coefficient of friction of Alumina Ball versus Composite 1 for dry sliding speeds of 40 rpm to 10 rpm.

Figure 4: Coefficient of friction of Alumina Ball versus Composites 1 and 2 for dry sliding speeds of 10 rpm to 1 rpm.

pin for the same geometry, except for a different range of friction force values. It was seen that the effect of damping due to pin geometry played a significant role in the magnitude of the amplitude of the wave packet for similar type of materials. The human molar pin, being functionally gradient with a softer dentin inside and a layer of enamel outside, produced resonance patterns with amplitude variations of up to ±75% at maxima. Further, the maximum amplitude of friction force traces was directly proportional to the normal load used in sliding contacts. Lower ranges of friction force values correspond to lower loads of 10 and 5 N, respectively, for the

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Figure 5: Friction force plots of Composites 1 and 2 versus Enamel Pin at 10–40 rpm in dry sliding conditions.

Figure 6: A single wave train for the dry sliding of Alumina Ball versus Composite 1 at 10 rpm indicating resonance.

set of materials used here. In general, the friction force trace for polymer composites is stable without oscillations only at ~ 35 rpm and above. This holds true in dry as well as wet environments like distilled water. Needless to say, only 15 N tests will be discussed henceforth for clarity and amplitude of signatures. When ceramic discs like alumina or porcelain slide against a ceramic pin, there is no distortion at any of the sliding speeds chosen as above. However, Composite 2 does show a wave

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packet like distortion with a much lesser amplitude than Composite 1 due to a lower polymer binder content, for the same sliding speeds, thus confirming the viscoelastic influence of the polymer on the anomalous friction traces. This is evident from Figures 4 and 5. For composite 1 against alumina ball in dry conditions, when the speed of testing was further lowered to 5 rpm, the wave train had an alternating strength of amplitude that resembled one with a carrier/modulator ratio of 5, what one exactly comes across in wave transmission. When the rpm was reduced to 1, the wave train pattern completely disappeared, and only a single waveform was seen to occur exposing the linear viscoelastic response signal of the polymeric solid to the load applied (see Figure 7).

Figure 7: Coefficient of friction plots for dry sliding of Composite 1 vs. Alumina Ball showing a single stress wave at 1 rpm.

Schematically, this phenomenon is explained as shown in Figure 2, where the vibrational resonance due to the sinusoidal viscoelastic stress wave propagation is shown to arise from a 1:1 ratio between the viscoelastic wave length and the length of the circumference of the wear track on the disc at 10 rpm. When the viscoelastic response wavelength increases marginally at 5 and subsequently at 1 rpm, the resonance pattern disappears completely as the single viscoelastic stress wave manifests out of the packets due to a higher wavelength than the circumferential length. Since composites with various surface roughness values at various stages of experimentation were employed in the study, it can be seen that the frictional force values are different along the time axis due to “wearing in,” but the amplitude and wavelength are consistent

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with the material properties, load, and speed of testing as conditions. A viscoelastically distorting second phase is sometimes incorporated forming a frictionally different surface layer that is prone to wear, which can easily be inferred when the force traces transit. It is envisaged that each polymeric material or its composite produces its own characteristic signal that is a signature whose wavelength and amplitude depend on the normal load. The nature and contact area of the pin/ball affect the amplitude of the 10 rpm resonance patterns due to the difference in vibration modes, but it has very little influence at 1 rpm due to the absence of the same. The sinusoidal waves resemble the stress waves which propagate in linear viscoelastic solids obeying a Maxwell or Zener/Burger parameter model under stretching. Since sliding wear gives rise to tensile forces at the surface due to contact stretching and shear forces with a strong gradient at a sub-surface plane, the same is manifested in the present case. A five-parameter model for hygrothermally degraded polymer, explaining every aspect of the observed phenomena for certain type of polymeric materials, is envisaged for future work. The viscoelastic response of a polymeric material against a surface that distributes load in sliding contacts is the cause for such waveforms. The present viscoelastic behavior is seen to be (a) consisting of dilational and shear waves (see Figure 8), (b) producing subsurface shear waves, (c) a spring and dashpot model-based manipulation, (d) a secondary and segmental in polymer relaxation, and (e) a viscoelastic version similar to the Tomlinson and Frenkel–Kontorova atomic frictional models presented in Figure 9 [7]. Dilatational

Shear

u

Vp

Vs P-waves

z

S-waves

(a)

(b) Surface

u

E,V,P

z Rayleigh wave (c)

Figure 8: A schematic drawing of dilational, shear, and Raleigh waves generated in sliding contacts.

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m

k

m k

m k

m k

m

Figure 9: A schematic drawing of the Tomlinson and Frenkel–Kontorova atomic friction model.

Self-organization can be adapted for the polymer molecular structures here, where the substrate is presented as a periodic energy profile created by the molecules, using the “m” or mass in the Tomlinson–Frenkel–Kontoraova model as a viscous dashpot and “k” the spring constant in series. This is similar to the Maxwell model where the dashpot and the spring are in series. The stress relaxation implies that the stress is time-dependent and varying as the pin moves around the disc surface in circles, causing the stress to increase and decrease due to instantaneous contact. Further, the strain that is developed is instantaneous in a POD experiment right under the pin at the interface and is almost negligible at the incipient or far behind locations. Hence, the strain in this case is localized, and the viscoelastic response models are also localized like a surf-riding situation. The developed stress waves behave like a fatigue wave train. Surface Raleigh waves are generated as shown in Figure 9 which can be used for in situ NDT (nondestructive testing) inspection. Though there is self-organization, over a longer time, thermal and hygrothermal effects can relax the stress further, causing hygrothermo-mechanical fatigue. In short, the rpm speed at the given radius/radii and the resulting sliding velocity was comparable to the relaxation time, τ, of the polymeric solid for the conditions that allow such a viscoelastic reaction to take place. Normally, the mechanical relaxation time (not volume) for a glassy polymer below its glass transition temperature ranges from seconds to minutes [8–10], and the evaluation of relaxation time, τ, for a polymer filled with inorganic particles, based on the relationships for a linear viscoelastic solid [8, 9], gives us a static frequency range of ω = 0.1–1 for tan δ = 0.001 to 0.1 as a dynamic mechanical analysis (DMA) test would prove for polymers. The relationship ωτ = 1 gets us an approximate value of 1–10 s for the relaxation time for these two polymer composites. Since there is time (t ≫ τ) for viscous reaction to take place at a low rpm value of 1 (for radius of 4–5 mm), the time-dependent stress, σt, drops and rises depending on the relaxation and recovery times. It is observed that this is not a stick-slip behavior which manifests as a saw-tooth waveform in the wear of materials but a sinusoidal stress wave as a result of viscoelasticity of the polymeric material. When the rpm increases, the material behaves elastically since the time for such a viscous reaction to take place is not available, as t ≪ τ. At an intermediate 10 rpm speed, the resonance occurring due to the viscoelastic response of the material was not noticed in the 8 month distilled water aged Composite 1 samples as the wavelength of the friction force trace was obviously longer due to time-dependent viscoelasticity, and the ratio for resonance was not met with. It leads us to believe that the viscoelastic response curve of an non-aged specimen at

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10 rpm is much shorter in order to obtain a wave train as shown in Figure 6, thereby rendering support to the evidence that vibrational resonance due to viscoelastic response of a polymer composite material to loading occurs when t = τ. The condition for resonance, in order to obtain such a wave train, is very much similar to the Maxwell resonance condition for oscillation of fields as given in Feynman lectures [11]: ω0 = 2.405 fc=rg

(1)

where ω0 is the resonant frequency, c the velocity, and r the radius of the wear track that was discussed [9]. It is seen that the constant 2.405 can be interpreted as the result of the path length of the wave train divided by the path length of the individual viscoelastic signal, which is in fact the condition for resonance. The radius of the disc can be substituted for r to obtain the condition for resonance. It is indeed interesting to note the similarity between acousto-mechanical and electromagnetic resonance conditions. The Maxwell resonant frequency in the present investigation, ω0, would be less than 5 Hz in this case when we substitute for c and r. Here, the linearviscoelastic stress waves are in packets at certain speeds of sliding and represent the viscoelastic and resonant stress wave propagation in the polymeric solid due to sliding contact. As discussed earlier in Figure 2, the phenomenon of resonance originates due to the coincidence of the viscoelastic signal wavelength with the perimeter of the wear track, or in other words, one rpm. The smooth attenuation of the friction force traces at rpm closer to 40 is a result of an elastic behavior as discussed before. Further, dynamic damping can occur when the material is both dissipative and dispersive [10] causing attenuation of the friction force traces due to the dilational stress component reducing and the shear stress component taking over. At higher loads and lower rpm, the attenuation might be advanced. It is expected that the surface Raleigh waves generated due to friction play a role in resonance at higher speeds and not in the viscoelastic response at low rpm [12]. An acceptable level of treatise is presented on polymer tribology by Sinha and Briscoe [13]. But this book does not deal with viscoelasticity or the effect of aggressive environment on polymer tribology. It is proposed to conduct monolithic unfilled polymer sliding contact tests in a linear reciprocating wear tester and confirm the precision and accuracy of the viscoelastic signals, relaxation, and retardation times and resonance conditions which would lead to the design and manufacture of viscoelastic testers that can correlate the viscoelastic properties with the mechanical properties and predict the thermo-mechanical behavior of polymers under controlled environment. At sub-zero temperatures, the threshold transition from viscoelastic to elastic behavior can also be predicted in the presence of a ductile to brittle transition. Viscoelastic response can also be appreciable when the hygrothermal attack on restoratives and other polymer composites is appreciable. A detailed account of the do’s and don’ts that involve the required specifications for hygrothermal conditioning, postsaturation equilibration, and tribology of polymer composites is presented in the investigations as done earlier [14, 15]. As viscoelasticity

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is appreciable in the postsaturated and water-equilibrated polymers and restoratives, these two references are considered significant. It is ascertained that it is not the machine natural frequency which falls between 50 and 1500 Hz as reported in literature for similar machines [16], but a viscoelastic phenomenon whose relaxation times and resonant frequencies with the POD geometry is much lower as evaluated here.

5 Erratum in existing literature and scope Many publications have emerged in the last few decades that have either chosen to ignore or just ignored the important aspect of viscoelastic interactions and mechanisms in sliding contacts and wear of polymeric solids. Books, book chapters, and research articles by tribology researchers have ended up measuring, assessing, and evaluating wear, lubrication, and friction in polymeric solids without considering the appreciable effects of viscoelasticity on these parameters [17–23]. As the friction force traces in the low speed domain are significantly dependent on the viscoelastic response of the material to sliding contact, any measurement of the friction force traces that ignores these aspects without a regard for sensitivity is bound to be erroneous. Wear rates and wear volumes too depend on the material removed, and the material just displaced out of the wear track due to viscoelasticity. Hence, their measurement too is a suspect. Though viscoelasticity of polymers is a known phenomenon, it has not been seriously considered by tribologists and machinists as a significantly contributing subject in the evaluation of polymeric solids and their applications. The publications chosen here to highlight the issue are only an act of serendipity and not choice. The real number is staggering and needs withdrawal or revision of the data and the publications, if the conditions stated in this chapter are encountered. The scope of viscoelasticity-based studies is very vast as polymeric solids are known to be hygrothermally susceptible that renders them nonlinear – a more complicated deviation from their linear viscoelasticity which is exhibited by rigid polymers and their composites at normal pressures and room temperatures. As nonlinear viscoelasticity demands the use of five-parameter models and similar conformations in series or parallel, lot of scope exists in the study of these mechanisms in the tribological modeling of such systems. The next section provides more detail about the mechanisms and applications of this phenomena in tribology and machining.

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6 Applications of the viscoelasticity phenomena in sliding contact The following are some of the salient features and applications of the discovery of the phenomenon of viscoelasticity in sliding contact mechanisms; 1. It provides a quick test method to assess the viscoelastic response of polymeric solids to sliding contact mechanisms. 2. A correlation of the viscoelastic properties with the mechanical properties is possible that would help in evaluating the mechanical properties of a polymeric solid from a knowledge of its viscoelastic response. 3. It is proposed as a single test that would evaluate the quasi-static mechanical properties and the tribological properties with an acceptable level of approximation. 4. A linear reciprocating wear test apparatus with an associated specific software would suffice to achieve this phenomenally easy way of evaluating the mechanical properties of a solid polymer. 5. This method serves as an easy to perform substitute dynamic mechanical analyzer as the relaxation and retardation times can be evaluated with an approximate assessment of the storage and loss modulus. 6. It helps in a quick materials selection process for ductile and ductile–brittle solid polymers with viscoelastic properties. 7. A detailed study of viscoelastic fatigue is possible as an outcome of this investigation. A viscoelastic thermal or hygro-thermal cut off can be evaluated in a tribological test where thermal or hygorthermal frictional softening effects could be quantified and the design limits, set to a required level.

7 Summary and conclusions This investigation on sliding contact friction of polymeric solids illustrates and explains the existence of viscoelastic response through analysis of the friction force traces that result from contact sliding under loads. The factors influencing the characterization of the viscoelastic and elastic properties of polymeric solids in sliding contacts viz. the relaxation time, the viscous reaction due to ageing and condition for resonance, are discussed. The Maxwell and other relevant models that seek to explain this phenomenon are highlighted and explained. It is proposed to use this phenomenon to evaluate the elastic and viscoelastic properties of virgin polymers and filled polymers with various processing, testing, and environmental conditions to aid in their complete hygrothermo-mechanical characterization through an understanding of sliding contact mechanics. The salient applications of the discovery of viscoelastic phenomena in sliding contacts are also predicted.

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References [1] [2] [3]

[4] [5] [6] [7] [8] [9] [10] [11] [12]

[13] [14] [15] [16]

[17] [18] [19]

[20]

[21]

Drozdov, A. D., Viscoelastic Structures, Academic Press, New York, 1998. Findley, W. N., Lai, J. S., and Onaran, K., Creep and Relaxation of Nonlinear Viscoelastic Materials, Dover, New York, 1989. Torskaya, E. V. and Stepanov, F. I., Effect of surface layers in sliding contact of Viscoelastic Solids ( 3D Model of Material), Frontiers in Mechanical Engineering, 09 May 2019, doi: https://doi.org/10.3389/fmech2019.00026. Carbone, G. and Bottiglione, F., Editorial: Adhesion, friction and lubrication of viscoelastic materials, Lubricants, 2021, 9, 23. Roylance, D., Engineering viscoelasticity, MIT's Department of Materials Science and Engineering, 2001. Krishnan, P., Rheology of epoxy/rubber blends, In: The Handbook of Epoxy Blends, Parameswaranpillai, J., Ed., et.al., Springer, Switzerland, 2017, 185–210. Weiss, M. and Elmer, F. J., Dry friction in the Tomlinson-Kontoraova-Frenkel model: Static properties, Physical Review B, 1996, 53, 7539. Matsuoka, S., Relaxation Phenomena in Polymers, Chapter 3: Glassy State, Hanser Publishers, Munich, 1992, 80. Kolsky, H., Viscoelastic Waves, International Symposium on Stress Wave Propagation in Materials, In: Davids, N., Ed., Interscience Publishers Inc, New York, 1960, 59. Perepechko, I. I., An Introduction to Polymer Physics, Mir Publishers, Moscow, 1981, 209. Feynman, R. P., Leighton, R. B., and Sands, M., The Feynman Lectures on Physics Vol:2, Mainly Electromagnetism and Matter, Narosa, New Delhi, 1995, 1049. Nosonovsky, M. and Mortazavi, V., Friction-Induced Vibrations and Self-Organization Mechanics and Non-Equilibrium Thermodynamics of Sliding Contact, CRC Press, FL, USA, 2014. Sinha, S. K. and Briscoe, B. J., Polymer Tribology, Imperial college Press, London, 2009. Padmanabhan, K., Comments on standards on restoratives, Indian Journal of Dental Research, 2009, 20(4), 514. Padmanabhan, K., The need to revise standards on dental restoratives – a commentary, Current Science, 25 August 2006, 91(4), 418. Bergantin, R., Maru, M. M., Farias, M. C. M., and Padovese, L. R., Dynamic signal analyses in dry sliding wear tests, Journal of the Brazilian Society of Mechanical Sciences and Engineering, Sept 2003, 25(3), doi: https://doi.org/10.1590/S1678-58782003000300011. Menezes, P. L., Nosonovsky, M., Ingole, S. P., Kailas, S. V., and Lovell, M. R., Tribology for Scientists and Engineers, Springer, 2013, 295–340. Nak-Ho, S. and Suh, N. P., Effect of fiber orientation on friction and wear of fiber reinforced polymeric composites, Wear, 1979, 53(1), 129–141. Vižintin, J., Kalin, M., Jahanmir, S., and Dohda, K., Tribology of Mechanical Systems: A Guide to Present and Future Technologies, American Society of Mechanical Engineers, USA, 2004. Nagarajan, V. S., Hockey, B. J., Jahanmir, S., and Thompson, V. P., Contact wear mechanisms of a dental composite with high filler content, Journal of Materials Science, 2000, 35(2), 487–496. Lee, J. H., Xu, G. H., and Liang, H., Experimental and numerical analysis of friction and wear behavior of polycarbonate, Wear, 2001, 251(1–12), 1541–1556.

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[22] Moreau, J. L., Weir, M. D., Giuseppetti, A. A., Chow, L. C., Antonucci, J. M., and Xu, H. H. K., Long-term mechanical durability of dental nanocomposites containing amorphous calcium phosphate nanoparticles, Journal of Biomedical Materials Research. Part B, Applied Biomaterials, April 2012, doi: https://doi.org/10.1002/jbm.b.32691. [23] Rutherford, K. L., Trezona, R. I., Ramamurthy, A. C., and Hutchings, I. M., The abrasive and erosive wear of polymeric paint films, Wear, 1997, 203–204, 325–334.

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Investigation of mechanical properties of rice straws and rice husk reinforced hybrid polymeric composite Abstract: Over the last few decades, the increasing environmental concerns have received enormous attention to the utilization of natural fibers as an alternative and attractive source of fiber materials. Natural fibers have the benefit of being both costeffective and environmentally beneficial. In the present work, one such noble attempt has been taken toward the development of rice straw (RS) and rice husk (RH)embedded hybrid polymer composite materials. Agricultural wastes like RS and RH as natural fiber have been utilized for the development of such RS–RH-reinforced hybrid composites that are environment-friendly and biodegradable in nature. The present work is an attempt in understanding the applicability of RS–RH-reinforced hybrid composite on the basis of various researches that have been published separately. The current work highlights the enormous increase “in mechanical properties such as tensile strength, flexural strength, flexural modulus, and young’s modulus (E)” of the prepared composite samples having a single layer, double layers, and triple layers of fiber (RS + RH) reinforcements oriented in unidirectional and in a bidirectional manner. In the current study, RS–RH-reinforced hybrid composite with a 30% volume fraction incorporated into epoxy resins that have been treated with NaOH solution has higher “tensile strength, flexural strength, flexural modulus, and young’s modulus” than other composites, according to the current study. The work discusses the various aspects of RS–RH hybrid composite on the basis of different mechanical testing such as tensile and flexural tests in order to analyze the mechanical behavior and material characteristics. Keywords: Rice husk composite (RHCS), rice straw composite (RSCS), rice straw–rice husk (RS–RH)-reinforced hybrid composite, rice straw biodegradability, RS–RH mechanical properties, tensile strength of RH, flexural strength of RH, flexural modulus of RH, Young’s modulus of RH, tensile strength of RS, flexural strength of RS, flexural modulus of RS, Young’s modulus of RS

Ranjan Kumar, Birla Institute of Technology, Mesra, Ranchi, Jharkhand 835215, India, e-mail: [email protected] Chikesh Ranjan, Birla Institute of Technology, Mesra, Ranchi, Jharkhand 835215, India, e-mail: [email protected] Kaushik Kumar, Birla Institute of Technology, Mesra, Ranchi, Jharkhand 835215, India, e-mail: [email protected] https://doi.org/10.1515/9783110724684-004

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1 Introduction Since ancient times, mankind is associated with the utilization of naturally occurring composite materials for various purposes in their day-to-day activities. The strawreinforced bricks were the earliest known composite utilized by mankind [1]. In recent years, the growing demand for an alternate source of attractive materials having thermo-mechanical properties carrying the desired performance is forcing researchers to develop economical, eco-friendly materials for sustainable development [2]. In this regard, the development of composite and hybrid composite materials has brought a remarkable revolution in the domain of material science and applications, which possess numerous domestic and industrial applications in various fields [3]. The rising environmental concerns are bothering scientists and researchers regarding the alternate utilization of agricultural organic wastes. Such agricultural organic wastes are produced by different crops like sugarcane, rice straw (RS), rice husk (RH), wheat, and coconut. In India, the annual production of stubble waste is about 320 metric tons harvested from rice/paddy, wheat, barley, etc. [4, 5]. Most of these wastes remain unused and are dumped and burnt in the open air which is one of the major causes of an increased pollution index. Therefore, the ecological consciousness has pushed us toward the quest of utilizing these agricultural waste residues in such a way that can be proven to be a source of new alternative materials with appreciable efficiency and desired thermo-mechanical properties [6]. These two natural fibers, RS and RH, fall under the non-wood biofiber family which has a large-scale production. Due to having such easy availability, such biofibers are opening tremendous opportunities for developing RS–RH-embedded reinforced composite materials which are comparatively much more economical than wood. Such RS–RH-embedded hybrid composites are proved to be a revolutionary path toward the reduction of environmental pollution and the produced agricultural wastes in the form of RS and RH can turn out to be a source of generating profitable revenue. Such man-made hybrid composite (RS–RH-reinforced polymer composite) possess intrinsic properties of having “high calorific power (about 4000 kcal/kg), low thermal coefficient, hardness, fibrousness, and abrasive nature. Such hybrid composite comprises potential applications as building panels for brake pads, thermal and acoustic insulation, etc.” [7–12]. The utilization of RH as biomass fuel is also a remarkable utilization for both industrial and domestic heating purposes [13], but after burning, a new form of residue i.e. ash, gets obtained which contains 80–90% of silica contents. The obtained ash with silica contents has chemically etching resistant, thermal shocks (above 600 °C) characteristics with relatively lower mechanical and thermal properties that made it quite suitable for developing ceramic materials. “The RH possesses a thermal conductivity ranging from 0.064–0.093 W/M2” [14]. Similarly, the RS-reinforced composite materials possess various improved characteristics, and their potential applications have been explored in various fields of applications. The

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potential utilization of RS–RH-reinforced composites in various domains as well as their application-based utilization has been delineated in Figures 1 and 2, respectively.

90 80 70 60 50 40 30 20 10 0

En En En B M En A C C M A C M C G N M C M Ph B M En P ym vir gin erg iote ate gin gric ate hem reen ate gron hem hem onst ioch ate gin lysic ano ulti hem icro ysic er onm eer y F chn rial eer ultu rial ist Su rial om ist ist ruc em rial eer s A scie dis ist bio s C ry s s r y r y ti r c p s s u o i Sc i i o s r Ap Ph on stry Sci ing C plie nce iplin y Or logy nde ien enta ng C els log Scie ng E al E Scie Mu tain Scie y y A n nv ng n pl ys Bu M en ns ivi d Na ary gan a n ce l S he l c ied ica il ed o l n cie m e pp ce M iro ine ce P tidis ble ce c ot Sc ic l... din lecu Te M nm er ap cip Sc o. lie nc ica ec i e . u x g ... i l i . l . t es ... ... ... . . .. l... ... ng ... ... ... .

Po l

Figure 1: Documents published on RS- and RH-reinforced composite in various domains [15].

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Co Bu nst i l d ru i n cti g . . on .

En Fu erg els y

En Ch gin em ee ica ring l

M Sc ate ien ria ce ls M ul ...

Figure 2: Various application domains of RS- and RH-reinforced composite [15].

The improved tensile strength of RS-embedded epoxy-based polymer composite has been noted and is utilized for making the composite particle board [16]. Similarly, the potential characteristics and applications for the RS-embedded polymeric composite have been explored in recent years. Similarly, the small-sized RH particle exhibits the remarkable “moisture resistant property as compared to the large-sized particles.”

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These small-sized particles are also utilized in developing vehicle bumpers which possess comparatively higher tensile strength [17]. Further, the studies reveal that the composite prepared with “RS-powder and poly(lactic acid)” exhibits improved characteristics of tensile and flexural strength [18]. The remarkable results have also been noted in the case of the composite prepared when the RS fibers are embedded with polypropylene and also the results exhibit the improved modulus [19, 20]. Hence, the investigations on individual RS- and RH-reinforced composites with different polymer matrix exhibits remarkable mechanical and thermal properties that are much useful in various domestic and industrial applications [21–23]. The utilization of such RS–RHreinforced hybrid composite has drawn great attention from researchers as an “alternative lignocellulosic raw material” for a potential replacement of wood for developing particle wood [24, 25]. The present work is such a modest attempt toward developing RS–RH-reinforced epoxy-based hybrid composite materials in order to study its mechanical properties and chrematistics in terms of tensile and flexural strength. The current section provides a brief introduction to the natural fiber-reinforced composites. In the next section, the classification of natural fibers along with the associated drawbacks and applications have been summarized. Further, the materials and methods along with the hybrid composite sample preparation methods have been briefly discussed for the current work. Further, in the subsequent sections, the final results and discussions as well as the conclusion have been summarized.

2 Natural fiber composites and its classifications 2.1 Drawback and applications The domain of natural fiber-reinforced composites (NFRCs) is being developed continuously according to the demand and industrial applications. However, it possesses some drawbacks that are essentially needed to be addressed in order to maximize its potential utilization as an alternative to synthetic fibers. The mechanical properties such as “tension, compression, fatigue, impact, blast and creep” of such NFRCs are most importantly needed to be addressed [26]. Currently, the lower mechanical strength and poor moisture-resistant properties of natural fibers put some limitation on their utilization in construction work and is currently used in the automobile sector, architectural work, and furniture making [27, 28]. The continuous development in NFRCs is opening new opportunities for expanding their application arena. “Its applications may include permanent form-works, facades, tanks, pipes, long span roofing elements, strengthening of existing structures, and structural building members” [29]. The geotechnical engineering is also interacting with the potential utilization of NFRCs. NFRCs possess some of the variables or process parameters that are necessary

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to be determined in order to analyze the overall properties, characteristics, and structure of a composite material. These parameters or variables are: “microfibrillar angle, cell dimensions, defects, and chemical composition.” Natural fibers possess some drawbacks when used as reinforcement in polymer composites. “Incompatibility between fibres and polymer matrices, tendency to form aggregates during processing, poor moisture resistance, inferior fire resistance, limited processing temperatures, lower durability, quality and price variation, and difficulty in using established manufacturing processes are just a few of them.” Such occurring incompatibility produces a “lower interface strength as compared to the glass or carbon fibres composites” [27, 28]. This drawback of natural fibers is due to their hydrophilic nature caused by the presence of “hydroxyl and some other polar groups.” Further, the poor processing and lower mechanical strength are due to having defects in terms of their exposure to moisture content during the fabrication process [30]. Furthermore, the bulk of natural fibers has lower degradation temperatures (200 °C), making them unsuitable for processing with thermoplastics at temperatures above 200 °C [26]. Surface treatments, resins, additives, and coatings are all examples of interfacial therapies that can ameliorate this condition [28, 31]. Despite the fact that NFRCs are less expensive than traditional “synthetic fibres.” The incorporation of various techniques and methodologies to overcome their shortcomings may incur additional costs. In order to compete with glass fiber composites, surface modification is required and is required to be optimized. Natural fiber prices fluctuate due to agricultural fluctuation and the difficulty of storing, transporting, and processing them. New applications can be regarded as newer opportunities to develop NFRCs in order to facilitate price reduction [28]. In addition, a thorough study of the composition of natural fibers as well as the various elements that influence their degradation is essential.

2.2 Classifications and degradation To gain a complete understanding of the degradation difficulties, it is critical to first comprehend the nature and compositions of natural fibers. Natural fibers are categorized according to their source: “plants, animals, or minerals.” Figure 3 exhibits a complete classification of natural fibers based on their origin. Proteins from hair, silk, or wool are used to make animal fibers [28, 32]. Bast fibers are the greatest choice for structural purposes. Flax fibers, for example, are inexpensive, lightweight, and have great strength and stiffness [28]. Natural plant fibers are used as reinforcements for polymeric composites in a variety of applications. “Plant stem or soft sclerenchyma (bast fibres), leaf, seed, fruit, wood, or cereal straw can all be used to extract natural fibres.”

64 Ranjan Kumar, Chikesh Ranjan, Kaushik Kumar

Figure 3: Schematic showing a detailed classification of fibers.

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Plant-based natural fibers are mostly made up of “cellulose fibrils embedded in a lignin matrix.” Figure 4 delineates a schematic structure of a biofiber. A primary cell wall and three secondary cell walls make up a layered structure of each fiber. The mechanical properties of fiber are determined by the thick central layer of secondary cell walls. It is made up of helically wound cellular microfibrils made of long-chain cellulose molecules. Cellulose, hemicellulose, and lignin are the three primary components of each cell wall. “Microfibrils (made up of cellulose molecules) act as fibres,” while lignin-hemicelluloses act as matrix [10, 17]. Pectins, oil, and waxes are among the other ingredients [17, 18]. Natural fiber has a hollow structure, unlike synthetic fibers, due to the presence of lumen.

Figure 4: Schematic structure of a biofiber [32].

NFRCs possess some of the variables or process parameters that are necessary to be determined in order to analyze the overall properties, characteristics, and structure of a composite material. These parameters or variables are: “microfibrillar angle, cell dimensions, defects and chemical composition” [28, 33]. The angle formed by the “fibre axis and microfibrils with a diameter of 10–30 nm” is known as the microfibrillar angle. The mechanical characteristics of fibers are determined by these microfibrillar angles. A smaller angle means more strength and stiffness, whereas a bigger angle means more ductility. Natural fibers with better mechanical strength often have a larger “cellulose content, a higher degree of cellulose polymerization, longer cell length, and a lower microfibrillar angle. As cellulose content and cell length grow, tensile strength and Young’s modulus” rise [32, 34, 35]. Further, the porosity developed in the fibers is due to the presence of voids. Plant-based

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fibers living in a wet habitats possess a high void content that results in the “higher moisture absorption” [36, 37].

3 Materials and methods 3.1 Rice straw RSs have been procured from the local village area and have been chopped in required dimension as shown in Figure 5.

Figure 5: Procured rice straws.

3.2 Rice husk Typically, in India, the RH is obtained during the manual harvesting of rice. RH is commonly used for burning in India that fuel up the issues of environmental pollution and produces the RH ash and requires a great attention due to its disposal difficulty. RH is basically utilized in silica form derived from itself and are utilized for different sets of physical and mechanical properties. The difference in geographical conditions helps in producing husk having different chemical composition of RH as given in Figure 6. “Naturally RH is tough, water insoluble, woody and has abrasive resistance behavior and silica-cellulose structure. The exterior is mostly silica coated with a thick cuticle and surface hairs, while small amount of silica is present in the mid region and inner epidermis.” Such differences in the chemical composition are due the varying climate conditions, various soil, and weather conditions.

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Figure 6: Chemical composition of RH [36].

3.3 Epoxy resins Epoxy polymeric resin (L-12) and the hardener (K6) have been utilized for the preparation of test samples. The resin and hardener have the pot life of 30–40 min, and 14–24 h are given for curing time under the ambient temperature of 25 °C. The properties of L-12 epoxy resin and K-6 hardener have been given in Table 1. In terms of mechanical strength, the epoxy resins provide higher mechanical properties than other resins such as vinyl ester or polyester. It also exhibits very low shrinkage after cure, moisture resistance characteristics, and superior fiber–matrix adhesion properties [38, 39]. Table 1: Properties of resins and hardener [40]. Specifications of resins and hardener Epoxy (L-) Properties Density (at  °C)

Unit

Range 

.–.

g/cm

Tensile strength

N/mm



–

Flexural strength

N/mm

–



–

Modulus of elasticity

N/mm

Hardener (K-) Density (at  °C)

g/cm

.–.

4 RS–RH hybrid composite preparation methods There exist various traditional composite manufacturing techniques that are capable of developing the composite materials. Some of the well-known techniques are: “resin transfer molding” (RTM), “vacuum infusion technique,” “compression molding technique” as well as the “traditional hand lay-up technique.” Over the last few decades, these techniques are very well developed and have been incorporated successfully to develop composite materials having high performance and desired quality

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benefits [41]. In the current work, the very “traditional hand lay-up technique” has been adopted to process the composite samples.

4.1 Hand lay-up technique This is a very common and oldest-known composite manufacturing technique for both small and large-sized products [42, 43]. At the start, an antiadhesive agent is applied onto the mold to prevent fibers from adhering to it. A thin layer of plastic sheet is also applied to the top and bottom mold surfaces to create a smooth surface for the composite component [44]. The desired size fibers are then placed on the bottom plate of the mold, and the resins mixed with other components are infused onto the layers of fibers, and the resins are uniformly disseminated over the fiber layer using a brush and roller. Following the development of this one layer, the additional layers of fibers or woven mats are oriented unidirectionally or bidirectionally on the previous polymer layer, and pressure is applied with the roller to eliminate any voids or air bubbles as well as excess polymer. Finally, the mold is closed, the pressure is removed, and the mold is allowed to cure at ambient temperature. Finally, the mold is opened, and the finished composite is extracted [45]. The mold prepared for hand lay-up composite manufacturing process has shown in Figure 7.

Figure 7: Mold prepared for the hand lay-up technique.

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5 Composite sample preparation RS was collected from the hamlet and chopped as needed (see picture 5). RS is a biodegradable plant-based natural fiber material. Natural fiber is utilized in composite materials as a reinforcing material. Also, the RH is not so easily degradable. The link that is formed between the natural fiber and the matrix is not flawless. The presence of lignin in natural fibers results in poor fiber–matrix bonding. The removal occurred as a result of insufficient bonding between the layers. Natural fiber treatment is really important for preventing this. The RS and RH fibers were treated with a 2% NaOH solution. RS was cleaned with fresh water after being treated with NaOH solution and dried in the sun for 8 h. The epoxy content for RS and RH fibers was 10%, 20%, 30%, 40%, and 50%. In a container, epoxy and hardener were combined well for 2–3 min. Figure 2 shows how to gradually apply the reinforce material and RS one by one. Finally, the mixture was allowed to harden for 24 h.

Figure 8: Prepared RS–RH composite samples.

6 Mechanical properties 6.1 Tensile and flexural strength test In case of a composite material, the factors such as “filler type, matrix material, concentration, size, and dispersion” as well as the adhesive were used between fibers and matrix. All these factors play a very versatile role in determining the tensile properties of a composite material. Various studies have been carried out toward analyzing the tensile behaviors of both RS and RH-based composite materials. A considerable finding on RH-based composites has been extensively investigated by a Korean team [46]. The “higher filler loading levels of RH fibres” had a negative impact on the tensile strength of the composite. Because of the higher filler loading, the material becomes brittle as the fraction of polymer (thermoplastic) decreased.

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Similarly, other significant mechanical qualities are the flexural properties, which must be understood before employing the composite for any application [21]. Flexural stiffness and strength are not the fundamental material qualities. They are the combined effects of a material’s basic tensile, compressive, and shear properties. In the present work, the tensile strength of the RS–RH-based hybrid composite has been investigated, and the experimentation has been carried out using the Instron Universal Testing Machine, manufactured by Instron Ltd, UK, as per the standards and guidance provided by ASTM D 638 as shown in Figure 8. Similarly, for estimating the flexural behavior, the three-point bending or flexural test was carried out under the standards and guidance provided by ASTM D790 as shown in Figure 9. (a)

(b)

Figure 9: Universal testing machine (a); (b) sample under loading condition.

7 Results and discussions The prepared RS–RH-reinforced polymeric hybrid composite samples were carried out for the tensile strength, Young’s modulus, flexural strength, and flexural modulus tests in both unidirectional and bidirectional manner.

7.1 Test results in unidirectional fibers arrangements 7.1.1 Tensile test The tensile testing was carried out for the prepared RS–RH-reinforced polymeric hybrid composite materials. The experimental result shows the variations occurred in the “tensile strength (σT) of composite with untreated fiber, hot water treated fiber

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Figure 10: Three-point bending attachment.

and 2% NaOH Treated fiber.” The σT of the hybrid composite dropped as the fiber volume percent increased due to inadequate bonding between the RS–RH fillers and epoxy matrix as shown in Figure 11. The graph depicts the highest σT for “30 percent of composite fibre volume treated with NaOH.” Because of the increased filler volume, σT has improved. It is also worth noting that σT has “decreased from 31% to 50%.” This is due to the higher filler volume, which diminishes the resin matrix’s presence. With increasing filler volume percent in the composite, σT dropped. 16

Tensile Strength N/mm2

14 12 10

Composite with untreated Fiber

8

Composite with Hot water treated Fiber Composite with 2% NaOH treated Fiber

6 4 2 0 0%

10%

20% 30% 40% 50% Fiber Volume Fraction %

60%

Figure 11: Plot of the tensile strength in unidirectional fillers arrangement.

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7.1.2 Flexural test The experimental shows the variations occurred in flexural strength (σF) of the prepared RS–RH-reinforced hybrid “composite with untreated fibers, hot water treated fibers and the fibres Treated with 2% NaOH.” The σF of the hybrid composite dropped as the fiber volume percent increased due to inadequate bonding between the RS–RH fillers and epoxy matrix as shown in Figure 12. As per the graph, the maximum flexural strength is obtained in case of the fillers having 33% of RS–RH fibers treated with NaOH. It is also worth noting that σF has “decreased from 31% to 50%.” The presence of resin between the filler material is reduced as the filler volume increases. The value of σF dropped as the volume percentage of filler materials (RS–RH) in the composite increased. 35

Flexural Strength Mpa

30 25 20

Composite with untreated Fibre

15

Composite with Hot water treated Fibre

10

Composite with 2% NaOH treated Fibre

5 0 0%

10%

30% 40% 50% 20% Fiber volume Fraction %

60%

Figure 12: Plot of the flexural strength.

7.1.3 Flexural modulus test Figure 13 depicts the decrease in flexural modulus caused by greater fiber volume contents and poor bonding between the RS–RH fillers and epoxy matrix. The greatest flexural modulus is achieved from the NaOH-treated fibers with a 30% fiber content as shown in the graph. In addition, the flexural modulus dropped “from 32% to 50%.” The presence of resin between the filler material is reduced as the filler volume increases. The flexural modulus of the manufactured hybrid composite samples decreased as the volume percentage of filler components (RS–RH) rose.

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4000

Flextural Modulus Mpa

3500 3000 2500

Composite with untreated Fibre

2000

Composite with Hot water treated Fibre

1500 1000

Composite with 2% NaOH treated Fibre

500 0 0%

10%

20% 30% 40% 50% Fiber volume Fraction %

60%

Figure 13: Plot of the flexural modulus.

7.1.4 Young’s modulus test Figure 14 shows that the NaOH-treated fibers with a 30% fiber content have the highest Young’s modulus. Because the filler materials had a higher volume fraction, the Young’s modulus increased. There is also a 35–50% reduction of the prepared RS–RH-reinforced hybrid composite’s Young’s modulus. 1600

Young’s Modulus Mpa

1400 1200 1000

Composite with untreated Fibre

800 600

Composite with Hot water treated Fibre

400

Composite with 2% NaOH treated Fibre

200 0 0%

10%

20%

30%

40%

Fiber volume Fraction % Figure 14: Plot of the Young’s modulus.

50%

60%

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7.2 Test results in bidirectional fiber arrangements The experimental estimates the variations in the tensile strength of manufactured single-layer bidirectional RS–RH-reinforced polymeric hybrid composite “with untreated fibre, hot water treated fibre, and NaOH treated fibre with volume fractions of 0%, 10%, 20%, 30%, 40%, and 50%.”

7.2.1 Tensile test for single layer Figure 15 depicts the maximum tensile strength of fibers with a volume content of 20% that have been treated with NaOH. The larger filler volume content is responsible for the increase in tensile strength. σT also “decreased from 21% to 50%,” as shown in the graph. This is due to “increased filler volume contents with less crosslayer bonding, which minimizes resin presence between the filler materials and the polymer matrix.” The σT of the composite dropped on increasing the filler volume fractions. Single Layer Bidirectional Continuous RS-RH Fibers (A) 16 Tensile Strength Mpa

14

Composite with untreated Fibre

12 10

Composite with Hot water treated Fibre

8 6

Composite with 2% NaOH treated Fibre

4 2 0 0%

10% 20% 30% 40% 50% RS-RH Fibers Volume Fractions (%)

60%

Figure 15: Plot of tensile strength in single-layer bidirectional fillers arrangement.

7.2.2 Tensile test for double layer The curve delineated in Figure 16 shows the highest σT at fibers with a “volume content of 20% treated with NaOH.” The greater filler volume contents are responsible for the increase in σT. Tensile strength was likewise reduced “from 30% to 50%” as shown in the graph. This is due to the larger filler volume contents having less crosslayer bonding, which minimizes the resin presence between the filler materials and the polymer matrix. σT dropped as the filler volume percentage in the composite increased.

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Tensile Strength Mpa

Double Layers Bidirectional Countinuous RS-RH Fibers (B) 18 16 14 12 10 8 6 4 2 0

Composite with untreated Fibre Composite with Hot water treated Fibre Composite with 2% NaOH treated Fibre

0%

10%

20%

30%

40%

50%

60%

RS-RH Fibers Volume Fractions (%) Figure 16: Plot of tensile strength in double layers bidirectional fillers arrangement.

7.2.3 Tensile test for triple layer The curve plotted in Figure 17 exhibits the maximum σT at fibers with a “volume content of 20% treated with NaOH.” The greater filler volume contents are responsible for the increase in σT. From the graph, it can also be seen that σT was likewise reduced “from 19% to 50%,” as shown in the graph. This is due to the larger filler volume contents having less cross-layer bonding, which minimizes the resin presence between the filler materials and the polymer matrix. σT dropped as the filler volume percentage in the composite increased.

Tensile Strength Mpa

Triple Layers Bidirectional Continuous RS-RH Fibers (C) 20 18 16 14 12 10 8 6 4 2 0 0%

Composite with untreated Fibre Composite with Hot water treated Fibre Composite with 2% NaOH treated Fibre 10%

20%

30%

40%

50%

60%

RS-RH Fibers Volume Fractions (%) Figure 17: Plot of tensile strength in triple layers bidirectional fillers arrangement.

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8 Conclusion We have come across a long way since the RS and RH are being utilized as a reinforcing fiber in composite manufacturing process. Various polymers have been utilized as a matrix material and have enormously contributed toward the reduction in the utilization of these harmful polymers. Natural fiber composites have opened up new possibilities for both researchers and companies in terms of sustainable manufacturing and use in the near future. As a result of these new pathways, the use of SFRCs as an alternative source of materials as a green product with ecological, environmental, and economic benefits has been recommended. In the current study, the prepared RS–RH-reinforced hybrid composite with 30% of volume fraction embedded into epoxy resins having treated with NaOH solution possess appreciable “tensile strength, flexural strength, flexural modulus and young’s modulus” than other composites. Further, the prepared composite having 20% volume fractions of fibers content with single, double, and triple layers of bidirectional composite treated with NaOH solution experiencing the more tensile strength than other composites. Therefore, The primary aim for developing such appealing RS-RH-based hybrid composites is to create a new generation of smart composites with applicability in a wide range of industries. However, future processing and improvements are still required that would necessitate further research.

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Vijayanandh R., Raj Kumar G., Arul Prakash R., Senthil Kumar M., Indira Prasanth S., Kesavan K., Balasubramanian S.

Optimizations on various lightweight composite materials under complex load using advanced computational simulation Abstract: The interaction between fluid and structure phenomena has influenced the majority of real-time challenges. Due to this interaction, the failure generating possibilities are quite high at aforesaid real-time problems such as train frontal affection, automotive vehicles issues, aeronautical impact loads, and wind turbine failure due to aerodynamic load interaction. Thus the studies about fluid–structure interaction (FSI) on various lightweight materials are very important, which can provide optimistic lightweight materials to withstand aerodynamic loads at all kinds of aforesaid industrial applications. The solution for such problems is based on continuum mechanics and is largely solved via numerical analysis in this study. It is a computational challenge to solve such problems because of the complex geometries, very complicated physics of fluid, and complicated fluid–structure interaction. The way in which the FSI is described gives a big opportunity to reduce computational errors. One possibility for reducing the effort of FSI is the use of one-way coupled approach–based simulation. This paper examines the aerodynamic load-based impact study on various composites using FSI analysis. The one-way coupling-based approach has been investigated at subsonic speeds through advanced computational simulations. ANSYS Fluent is predominantly involved in the estimation of aerodynamic pressure load on the conventional test specimen. Additionally, ANSYS Design Modeler tool is used for conceptual design construction and the various composites are generated in ANSYS ACP tool. Finally, the comparative Impact analyses are executed and thereby the suitable material for impact application is selected. Keywords: Aerospace, automotive, carbon fiber, CFD, FSI, epoxy resin, impact load, locomotive, glass fiber, Kevlar, polymer

Vijayanandh R., Department of Aeronautical Engineering, Kumaraguru College of Technology, Coimbatore, Tamil Nadu 641049, India, e-mail: [email protected] Raj Kumar G., Arul Prakash R., Senthil Kumar M., Department of Aeronautical Engineering, Kumaraguru College of Technology, Coimbatore, Tamil Nadu 641049, India Indira Prasanth S., Kesavan K., Department of Aeronautical Engineering, Kumaraguru College of Technology, Coimbatore, Tamil Nadu 641049, India Balasubramanian S., Department of Mechanical Engineering, Kumaraguru College of Technology, Coimbatore, Tamil Nadu 641049, India https://doi.org/10.1515/9783110724684-005

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1 Introduction 1.1 Aim To compute the comprehensive analyses on various composite materials under the effect of aerodynamic load (impact load) by using fluid–structure interaction (FSI)– based computational approach. Various composites, such as CFRP (Carbon Fiber Reinforced Polymer), KFRP (Kevlar Fiber Reinforced Polymer), and GFRP (Glass Fiber Reinforced Polymer), are used for their high impact strength, high tensile strength to weight ratio, and their being approximately 10 times stronger than steel. Additionally, this comparative mechanical behavior analysis is aimed to suitable lightweight material to withstand complicated aerodynamic-cum-impact load for various realtime applications; thus ASTM D7136-07 model [1] is influenced for the generation of test specimen. For entire behavioral investigation, the computational simulation has been implemented. The flow field of average working speed of 100 m/s (subsonic) is finalized and computed through CFD tool on different composite materials in order to extract the aerodynamic pressure on the test specimen. To determine the effect of coupling stress, the FSI method is implemented in ANSYS Workbench to calculate the stress caused by the pressure, in which one-way coupling method is approached for this subsonic speed. FSI can be stable or oscillatory, in which the oscillatory interaction, the strain induced in the solid structure, causes it to move when the stress is reduced, and the structure returns to its former state only for the process to repeat. Hence three parameters are mainly focused: stress, strain energy, and deformation [2].

1.2 Composite materials Composite materials have been currently most widely used in real-time complicated engineering applications due to their attractive properties like high strength to weight ratio and stiffness to weight ratio. The composite materials are made by combining two or more materials, each having different properties. They work together to give the composite unique properties. They are light as well as strong when compared with other metals. They are used for its light weight, strength to weight ratio, corrosion resistance, flexibility, stability, radar transparent and durability [3]. Usually reinforcements provide the strength and stiffness. Most of the time, reinforcements are harder, stronger, and stiffer then matrix. Epoxy matrix has been widely used due to its superior strength, light weight, and exceptional function at elevated temperatures. Typically used fibers include glass, carbon, and Kevlar. The matrix forms the continuous phase such as polymer, metal, or ceramic. Ceramics have high strength and stiffness, but they are brittle. Polymers have low strength and stiffness, while metal matrix has immediate strength and stiffness, but

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they are highly ductile. Glass, Kevlar, and carbon fibers are stronger than other matrixes due to their excellent stiffness and strength [4]. Carbon fibers are light fibers and they can be chosen depending upon the composite part being manufactured and the type of fiber material required. It has excellent impact properties which make them more advantageous. Its major advantage is that it has zero thermal expansion. They can resist very high temperature. If they are designed and dimensioned properly, carbon fiber composite structures do not suffer any fatigue issues. Glass fibers are cheap and beneficial for large structures. They have good chemical resistance to acids and solvents. They have low moisture absorption, high strength, heat resistance, high strength to weight ratio, and electrically insulating. They are easy to trim after curing and processes such as wet layup and resin infusion make them cost efficient. Kevlar fibers are light weight and have excellent tensile strength and are highly impact- and abrasion-resistant. Laminated Kevlar is very stable at high temperature. When it is used as composite with rubber, it retain its flexibility. In order to choose which composite is best suited for aerodynamic load–based impact analysis, FSI analysis has been approached on these three composites. A conventional shape-based element is used as a specimen, in which the following dimensions are obtained from ASTM D713607: length is 150 mm, breadth is 100 mm, and thickness is 10 mm [5, 6].

2 Problem identification solution techniques 2.1 Problem identification: issues of fluid load and impact load The impact load in the wider sense represents every sudden change in the already existing load, that is, the sudden start of a new load. The most important task in the impact analysis is to access the behavior of the structure during and after the impact. There is a significant change in the load intensity at the interaction region in a very short period of time. The exact calculation of the stresses arising as a result of impact is an extremely complex problem that is difficult to solve by using the usual method. In such difficult cases, FSI analysis provides a better and accurate solution [7]. The dynamic effects of impact load are very complex, and they are characterized by an even more complicated response of system. A large energy wave is converted into stresses in a very short time interval, followed by a large deformation that a structure or a structural component needs to withstand losing bearing capacity or stability. However these deformation and response differs at different speeds. The way of deformation at subsonic speeds may be different from that of supersonic speeds. Dynamic response of system implies a complex interaction of physicalmechanical characteristics of materials, along with geometric characteristics of the fluid elements [8].

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Mostly linear analysis shows that the response of the dynamic system to the effect of impact load can be successfully analyzed in several relatively simple ways with the help of software like Abaqus. They provide solutions of satisfactory accuracy. When it comes to a nonlinear calculation that includes the post-elastic behavior of material, the analysis becomes much more complex and practically impossible even for simpler systems [9]. Using modern software, nonlinear dynamic analysis is carried out without major problems. Also, for more complex linear systems, the application of the appropriate software is the only solution. It can be seen that the effect of damping in this issue is considerably lower. The largest part of the energy dissipated is done through deformation energy of the beam, as well as through friction and local plastic deformations, so the effect of damping can be ignored. Due to a large amount of kinetic energy dissipated at the very beginning, the vibration in this area is considerably smaller [10]. When it comes to stresses, especially at the point of impact, the correct answer can be given only by numerical analysis. It can be said that the application of the software in analyzing the impact load problem allows for a better understanding of the stress and gives a broader picture of the behavior of the structure during and after the load action [11].

2.2 FSI-based multi-objective optimization The ultimate outcome of this work is to give suitable load resisting lightweight material for aforementioned complicated-cum-impact load–based applications. In this regard, the multi-objective optimization–based investigation has been carried out on various composite materials with the help of FSI approach. The optimizations involved in this work are: the optimization is carried out on the selection of lightweight material to resist impact load, the optimization is carried out on the selection of suitable fibers to resist aerodynamic load, and the optimization is carried out on the selection of suitable direction of fiber to resist effectively against impact load. To engage all of the aforesaid optimizations, the boundary conditions of the computational simulations need to be given and transferred perfectly in order to achieve trustworthy results. For this investigation, a separate advanced simulation is carried out to attain the value of uniformly distributed load (UDL), which is computational fluid dynamic (CFD) simulation. To enhance the magnitude of UDL as well as intensity of the aerodynamic pressure, the compressible flow–based flow is picked as input to the CFD simulation. Therefore the force generation due to aerodynamic fluid is quite higher than normal fluids so this same external UDL input will be also applicable for other non-fluid load-based applications. Hence, the load transformation is a very tough process, which needs to be carried out in a perfect manner in order to get an acceptable solution. To transfer the load from fluid domain to structural domain, there are two primary categories: manual transfer and system-based coupled transfer. The probability of error creation is high in the manual transfer–based computation, and the probability

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of error creation is low in the system-based coupled transfer. So, the system-based coupled transfer is picked for this case, but this transfer is further classified into two: one-way coupling approach and two-way coupling approach. One-way coupling approach is based on the transferring principle of direct coupling, in which the fluid domain has been computed initially and thus the structural problem has been solved finally. Through this one-way coupling approach, the user has a time to counter check the attained CFD results in the perspective of whether the attained results are fulfilled the fundamental principles such as location of stagnation point and location of flow separation. While come to two-way coupling approach, the transferring principle has been computed with the help of a unique system coupling tool. In two-way coupling approach, the boundary conditions are separately given to both the fluid and structural domains and thereafter the simulations have been carried out in side-by-side by manner. If the given boundary conditions are true then only the system coupling tool of two-way FSI approach can provide convergence. Thus comparatively, two-way coupling is complicated one to execute but able to provide high reliable outcomes. The fluid environment is intentionally picked as compressible so the convergence of CFD problem needs to be checked before the structural simulation initialization. Thu oneway coupling-based FSI approach is most suitable for this multi-objective optimization; hence, the same method is implemented in this work. The work process for this comparative investigation is commonly revealed in Figure 1.

3 Methodology: fluid–structure interaction [FSI] The chosen hard challenge for this study is completely dependent on aerodynamic loads and failure generating variables, therefore powerful computational simulation can handle the problem perfectly. Further internal steps of this implemented advanced computational simulation are explained in the forthcoming subsections.

3.1 Physical model and control volume: both CFD and structure analysis The specimen has been modeled as per the dimensions of ASTM D7136-07. An enclosure has been created around the model which will act as a flow domain for the simulation. Then the Boolean is created where the target body is the domain and the tool body is the specimen so that they can be suppressed whenever necessary. The control volume is constructed as per the industry as well as academic levels, which is 20 times enlarged than length of the test specimen in main flow directions and 10 times enlarged than the length of the test specimen in side flow directions [16]. The shape of the control volume is constructed based on square base. As said

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Estimation of Design parameters of Test specimens

Generation of Test Specimen and Control Volume

Implementation of Properties for various COMPOSITE MATERIALS

Execution of Boolean Process [Eternal Flow Analysis]

Generation of Composite Test Model with the help of Composite Tool

Generation of FVM based Discretization for CFD Solver

Generation of FEM based Discretization for Structural Solver

Transformation of composite test specimen to FEA Solver

Compute the solution for Aerodynamic Pressure Post-Processing of Computational Model

Gereratio of Final FEA Computational Model

FSI Coupling on Composite Computational Model

Apply the Boundary Conditions in the FEA Model

FSI based Solution

Results generation Figure 1: Working flow of entire computational process.

earlier about the presence of Boolean, the area proximity region is created inside the control volume. The inlet and outlet denotations are give in the main flow stream and pressure far-fields are given at side flow streams. On the structural side, a layered composite structure has been modeled using the ACP software. The corresponding composite material has been defined in the engineering data as per the analysis requirement and the mesh is generated. The fabric, laminate, and orient material properties are given in the setup. Material and its thickness information are briefly described in the fabric part, and the fabrics are assembled with orientation in such a way that it would form like an exact composite. The layout area, layout directions, and Rosette/Edge set where the reference directions are defined has been given under the orient material. This ACP setup is then transferred to the static

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structural Model and the fluent data is extracted to its setup. The load and support are given in the respective area as per the need, and the specimen is fixed at the both ends. Finally the structure side is solved and the deformation and strain energy has been obtained [17].

3.2 Discretization The process of converting a physical model of a test specimen into a computational model is known as discretization. In computational simulation, the discretization is an unavoidable phase because the irresponsible physical model has been converted into responsible computational model for external loads. In this work, two different kinds of meshes are imposed for two different environmental conditions, which are mesh for fluid domain and mesh for structural domain. The mesh is generated where the mesh has been fine-tuned with relevant sizing. The fine unstructuralbased mesh facility is imposed for fluid domain and fine structural-based mesh facility is imposed for structural domain. The mesh quality is achieved the value of 0.96 for fluid models and 0.98 for structural models. Both of the achieved mesh quality values are within the allowed range, hence the authors are ready to run grid convergence tests to fine-tune mesh structures [18].

3.3 Boundary condition imposed: both CFD and structural analysis Based on the fluid flow (compressible flow) the density solver has been selected. Because of the implementation of density solver, the continuity, momentum, and general gas law relationships are implemented in the computation and very important to estimate the pressure on the test specimen. The test specimen is commonly in the shape of rectangular design; thus, the creation of turbulence is quite high so k-epsilon model is used in order to deal with external flow. At the FSI areas, which is a conventional test model, the “No slip” boundary condition is given, and the fluid velocity is given at a subsonic speed of 100 m/s. The second-order derivative is used as solution method. The fluid field is solved in the fluent tool after giving the necessary boundary conditions and finally pressure force is calculated. On the structure side, 10 reinforcement layers are assembled and thus the composite test solid model is generated. Fibers are arranged on unidirectional (UD) side through the help of rosette facility. Both the longer edges of the test specimen are arrested with fixed support. The outer surfaces of the entire test specimen are mentioned as FSI regions and thereby the aerodynamic loads are transferred on it. Apart from these conditions, the mechanical properties of composites play a major role. The properties are Young’s modulus, Poisson ratio, and bulk modulus [19–24].

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3.4 Governing equations For the FSI analyses-based computations, the following governing eqs. (1) to (7) are very important to compute this complicate problem. In which, first three equations are belongs for fluid computations and the next four equations correspond to structural computations [1–24]. ∂ρf + ∇.ðρ f vÞ = 0 ∂t

(1)

∂ρf v + ∇.ðρf vv − τf Þ = f t ∂t

(2)

∂ðρhÞ ∂p − + ∇.ðρf vhÞ = ∇.ðλ ∇TÞ + ∇.ðv.tÞ + v.ρ f f + SE ∂t ∂t τf = ð− p + μ ∇.vÞI + 2μe ··

ρs d s = ∇ · σs + fs

(4) (5)

8 τf .nf = τs .ns > > > > < d =d s f > q = q > f s > > : Tf = Ts ·

(3)

(6)

··

·

uΓ ðtÞ = dfΓ ðtÞ; uΓ ðtÞ = vΓ ðtÞ;u Γ ðtÞ = vΓ ðtÞ

(7)

3.5 Grid and sensitivity convergence tests Figure 2 is revealed the gird convergence test on KFRP, in which different six meshes are used. The equivalent stress in “kPa” is played the major role in the selection factor of this grid convergence test. The first mesh case is coarse level–based construction, the second mesh case is medium level–based construction, the third mesh case is fine level–based construction, the fourth mesh case is fine with refinement level–based construction, the fifth mesh case is fine with face level–based construction, and the sixth mesh case is fine with inflation level–based construction. The boundary conditions are maintained as common for all the six mesh cases and thus the computational results are carefully listed in Figure 2. From the figure, it is observed that mesh case IV is having the higher capacity to provide reliable outcomes than other mesh cases because the stress values are maintained same after case IV. After the successful completion of grid convergence test, the mesh case IV is finalized to implement in all other computational cases of this comparative investigation. But, one of the other factors also needs to be finalized before the main comparative investigation, which is the selection of optimum fiber thickness. Thus the

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Equivalent Stress in kPa

Grid Convergence Study of KFRP

10.8 10.6 10.4 10.2 10.0 9.8 9.6 9.4 9.2 9.0 8.8 8.6 8.4 CASE-I

CASE-II

CASE-III

CASE-IV

CASE-V

CASE-VI

Mesh Cases various from Case-I to Case-VI Figure 2: Grid convergence test of KFRP.

sensitivity test is organized on CFRP composite, in which six different various fiber thicknesses are implemented. As followed in the grid convergence test, in this sensitivity test also all the boundary conditions are maintained same for all the six different fiber thickness–based analyses. Total deformation is primarily focused and also plays a focal role as a selection factor for this sensitivity test. For all the six cases, the deformations are monitored carefully and thereby it is concluded that fiber thickness of 1 mm is suitable to construct the computational composite model in ANSYS ACP. Figure 3 is shown the second sensitivity test of this work, which deals the finalization of suitable fiber diameter for the development of composite laminates in ANSYS ACP. After the case IV of sensitivity test, the deformation remains the same; thus, the authors concluded at this stage that even the further reduction of fiber thickness will not affect the deformation value.

4 Results and discussions The comparative computational results are executed for all the primary composite materials under the aerodynamic loading conditions through computational FSI simulation. While coming to computational model construction, two different model generations are possible, which are length-wise fiber assembling and breadth-wise fiber assembling. Therefore, these comparative investigations are divided into two categories, which are completely discussed in this section.

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Total Deformation in mm

Computational Sensitivity Test 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 10

5

2.5 1 0.1 Various Thickness of CFRP-UD-Wet Fiber in mm

0.01

Figure 3: Computational sensitivity test.

4.1 Numerical results of subsonic region-100 m/s: lengthwise –

Carbon UD – Prepreg – 230 GPa

Figure 4: a) Equivalent stress, b) Strain energy and c) Total deformation.

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Carbon UD – Wet – 230 GPa

Figure 5: a) Equivalent stress, b) Strain energy and c) Total deformation.

–

Epoxy E-glass UD

Figure 6: a) Equivalent stress, b) Strain energy and c) Total deformation.

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Epoxy E-glass wet

Figure 7: a) Equivalent stress, b) Strain energy and c) Total deformation.

–

Epoxy S-Glass UD

Figure 8: a) Equivalent stress, b) Strain energy and c) Total deformation.

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Kevlar

Figure 9: a) Equivalent stress, b) Strain energy and c) Total deformation.

As discussed earlier, six different composite materials are underwent for both the length-wise and breadth-wise computations, in which two categories correspond for CFRP, three categories correspond for GFRP, and one material category corresponds for KFRP. Three important structural factors are considered for this work are equivalent stress, strain energy, and total deformation. Based on these factors’ generation levels, the best material is shortlisted through FSI simulation. Firstly, the lengthwise assembling is implemented and tested. Figures 4–9 reveal the lengthwise-based structural outcomes of conventional composite test specimen, in which Figures 4 show the results of Epoxy – Carbon UD – Prepreg – 230 GPa-based CFRP composite, Figures 5 show the results of Epoxy – Carbon UD – Wet – 230 GPabased CFRP composite. Figures 6 show the structural outcomes of Epoxy E-Glass UD-based GFRP composite, Figures 7 reveal the structural results of Epoxy E-Glass Wet–based GFRP composite, Figures 8 reveal the results of Epoxy S-Glass UD–based GFRP composite, and Figures 9 reveal the results of Epoxy-Kevlar-49-based KFRP composite. The comprehensive results of entire cases are shown in Figures 10 and 11.

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4.2 Comparative analysis lengthwise Comparative Analysis Lengthwise Total Deformation 11 10

Total Deformation in nm

9 8 7 6 5 4 3 2 1 0 CFRP-UD-Prepreg CFRP-UD-Wet

E-Glass-UD

E-Glass-Wet

S-Glass-UD

Kevlar-49

Various Composite Materials Figure 10: Comparative analysis of total deformation.

Comparative Analysis Lengthwise Equivalent Stress 9.8 9.7

Equivalent Stress in kPa

9.6 9.5 9.4 9.3 9.2 9.1 9.0 8.9 8.8 8.7 CFRP-UD-Prepreg CFRP-UD-Wet

E-GFRP-UD

E-GFRP-Wet

Various Composite Materials Figure 11: Comparative analysis of equivalent stress.

S-GFRP-UD

Kevlar-49

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4.3 Numerical results of subsonic region-100 m/s: breadth-wise –

Carbon UD – Prepreg – 230 GPa

Figure 12: a) Equivalent stress, b) Strain energy and c) Total deformation.

–

Carbon UD – Wet – 230 GPa

Figure 13: a) Equivalent stress, b) Strain energy and c) Total deformation.

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Epoxy E-glass UD

Figure 14: a) Equivalent stress, b) Strain energy and c) Total deformation.

–

Epoxy E-glass wet

Figure 15: a) Equivalent stress, b) Strain energy and c) Total deformation.

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Epoxy S-Glass UD

Figure 16: a) Equivalent stress, b) Strain energy and c) Total deformation.

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Kevlar

Figure 17: a) Equivalent stress, b) Strain energy and c) Total deformation.

Second, the breadth-wise setup is constructed and tested. The entire results of aforesaid materials [same as lengthwise case] are revealed in Figures 12–17.

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4.4 Comparative analysis: breadth-wise Figures 18 and 19 provide a comprehensive report of total deformations and equivalent stresses of breadth-wise constructed primary composite materials. Conclusively, the authors commented that KFRP-based composite can withstand aerodynamicbased impact load effectively than other composites. Comparative Analysis Breadth-wise Total Deformation 11 10

Total Deformation in nm

9 8 7 6 5 4 3 2 1 0 CFRP-UD-Prepreg CFRP-UD-Wet

E-Glass-UD

E-Glass-Wet

S-Glass-UD

Kevlar-49

Various Composite Materials

Figure 18: Comparative analysis of total deformation.

Comparative Analysis Breath-wise Equivalent Stress 9.8

Equivalent Stress in kpa

9.7 9.6 9.5 9.4 9.3 9.2 9.1 9.0 8.9 8.8 8.7 8.6 8.5 CFRP-UD-Prepreg CFRP-UD-Wet E-Glass-UD E-Glass-Wet Various Composite Materials

Figure 19: Comparative analysis of equivalent stress.

S-Glass-UD

Kevlar-49

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5 Conclusions A low probability of failure of object under complicated working conditions is the utmost concern has been involved in every domain. With this concern, this comparative investigation is computed on CFRP, GFRP, and KFRP through advanced-cumcombined computational facilities. For this work, the aerodynamic pressure–based sudden interaction is given as external load to the shortlisted test specimen. The test specimen is extracted from the conventional platform, which is ASTM D7136-07 [1]. Because a sudden interaction type of stress can occur in all kinds of difficult real-time systems, the common test specimen is employed in this comparison inquiry instead of a targeted test specimen. The initial platform of test specimen is modeled on ANSYS Design Modeler, and the remaining geometry is constructed with the help of ANSYS ACP. ANSYS Mesh Tool creates meshes for both the fluid domain and the structural domain. Thereafter, the fluid dynamic analysis on the test specimen is computed by using ANSYS Fluent. The aerodynamic pressure distributions over the entire test model are clearly predicted, which is used as uniformly distributed load [UDL] for the structural simulation. The UDL is perfectly transferred from fluid domain to structural domain by the facility called one-way coupling under the family of FSI investigations. Two types of fibers are assembled and thereby twelve different best composites are obtained as outcome of ANSYS ACP. From the comparative analysis, it is undoubtedly observed that KFRP is very stiffer and has a higher lifetime under any sort of complicated sudden external interactions. The deformations generated in KFRP are ten times lesser than both GFRP and CFRP, and the equivalent stresses induced in KFRP are three times lesser in CFRP and six times lesser in GFRP. Thus, the KFRP is suited to implement in aerospace structure applications, high-speed automotive applications, high-speed locomotive train applications, and complicated impact load–based industries.

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[17] Mohamed Bak, K., Raj Kumar, G., Ramasamy, N., and Vijayanandh, R., Experimental and numerical studies on mechanical characterization of EPDM/S-SBR with nanoclay composites, IOP Conference Series: Materials Science and Engineering, 2020, 912, 052016, 1–11, doi: 10.1088/1757-899X/912/5/052016. [18] Raj Kumar, G., Vijayanandh, R., et al., Comparative investigations on the main elements of carbon fiber based composites using computational structural simulations, IOP Journal of Physics: Conference Series, 1504 012003, pp. 1–11, 2020, https://iopscience.iop.org/article/ 10.1088/1742-6596/1504/1/012003 [19] Vijayanandh, R., Senthil Kumar, M., Naveenkumar, K., Raj Kumar, G., and Naveen Kumar, R., Design optimization of advanced multi-rotor unmanned aircraft system using FSI, Lecture Notes in Mechanical Engineering, eBook ISBN – 978-981-13-2718-6, Chapter number 28, 2019, 299–310, doi: 10.1007/978-981-13-2718-6. [20] Vijayanandh, R., Venkatesan, K., Senthil Kumar, M., Raj Kumar, G., Jagadeeshwaran, P., and Raj Kumar, R., Comparative fatigue life estimations of Marine Propeller by using FSI, IOP – Journal of Physics: Conference Series, 2020, 1473, 012018, 1–8, doi: 10.1088/1742-6596/ 1473/1/012018. [21] Mirrudula, P., Kaviya Priya, P., Malavika, M., Raj Kumar, G., Vijayanandh, R., and Senthil Kumar, M., Comparative structural analysis of the sandwich composite using advanced numerical simulation, AIP Conference Proceedings, 2270, pp. 040005–1 to 040005–5, 2020, https://doi.org/10.1063/5.0019370 [22] Venkatesan, K., Geetha, S., Vijayanandh, R., Raj Kumar, G., Jagadeeshwaran, P., and Raj Kumar, R., Advanced structural analysis of various composite materials with carbon nanotubes for property enhancement, AIP Conference Proceedings 2270, 030005 (2020), pp. 030005–1 to 030005–6, https://doi.org/10.1063/5.0019367 [23] Indira Prasanth, S., Kesavan, K., Kiran, P., Sivaguru, M., Sudharsan, R., and Vijayanandh, R., Advanced structural analysis on e-glass fiber reinforced with polymer for enhancing the mechanical properties by optimizing the orientation of fiber, AIP Conference Proceedings 2270, pp. 040006–1 to 040006–5, 2020, https://doi.org/10.1063/5.0019378 [24] Bhagavathiyappan, S., Balamurugan, M., Rajamanickam, M., Vijayanandh, R., Raj Kumar, G., and Senthil Kumar, M., Comparative computational impact analysis of multi-layer composite materials, AIP Conference Proceedings, 2270, pp. 040007–1 to 040007–5, 2020, https://doi. org/10.1063/5.0019380

Nisha Kumari, Kaushik Kumar

Investigations of mechanical properties of a hybrid nanocomposite for the development of lower body orthotic callipers Abstract: The present work has been done to investigate the potency of composite material with help of polymer matrix reinforced with graphene and coir fiber at both levels (macro and micro). Graphene and coir fiber are used as hybrid reinforcement and epoxy resin as a matrix to replace aluminum-based callipers which are currently used as an alternate material for polio survivors. By weight of epoxy as a matrix, the addition of graphene and coir was decided. Graphene added was 2% and coir fiber 10% respectively. Coir fibers were reinforced by hand lay-up technique also known as the molding process and graphene was dispersed using an ultrasonic sonicator. To ensure whether the samples used for testing are void-free fabrication was carried out under vacuum. Tensile testing and flexural properties were estimated and then results were compared with commercially used aluminum-based orthotic callipers. The current investigation exhibits the higher strength with relatively lower density and eco-friendly behavior of such natural fibers reinforced composites. Keywords: Orthotic callipers, polymer matrix, coir fibers, graphene, aluminum, tensile test, flexural test

1 Introduction The rising population has also led to numerous disabilities which are sometimes not taken care of when required the most attention. Disabilities may be physical, mental, or a combination of both conditions/impairments. Impairments may be present in an individual from birth or may acquire it during his/her lifetime due to disorders/disasters. Disorders may be of various types when related to different sense organs. In this paper, the authors are concerned about impairment related to legs which led to weak and feeble joints and needs support for functioning. Patients who find difficulty in their day-to-day activities and in moving from one place to another due to disability are taken into consideration. The main reason for such problems can be the disfigurement of legs, amputation, and underdevelopment. Such situations are faced by polio survivors as well due to which patients are in

Nisha Kumari, Medi-Caps University, Indore, Madhya Pradesh, India Kaushik Kumar, Birla Institute of Technology, Mesra, India, e-mail: [email protected] https://doi.org/10.1515/9783110724684-006

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need of an appliance that provides them support in the gait movement and gives strength to the weakened joints. Orthotic callipers are such appliances that aid in movement and locomotor disability. Orthotic callipers are applied externally in the place where joints are weak so that it aids in modifying the structural and functional characteristics of the neuromuscular and skeletal system. It may be also used in controlling, guiding, and limiting crippling and aids in rehabilitation from future injuries due to disability [29]. They also provide required strength and stiffness to the joints which become weak due to paralysis. Hence, the selection of the required callipers becomes one of the important factors for such patients as it will restrict their undesirable movement and resist their upper body weight. Such callipers are presently consisting of metallic braces attached sideways, a knee strap with an attached shoe [8, 37]. The side braces are presently made up of aluminum alloy. A typical commercially available calliper has been depicted in Figure 1.

Figure 1: Commercially available orthotic callipers.

Aluminum alloy is a metal that becomes heavy for the patients to carry. When they start gaining weight it is of no use to them as the metal callipers are unable to bear the weight of the patients. Due to this problem patients need to change their callipers every now and then. So, this requires solutions to overcome such issues. Callipers designed for polio survivors must inherit certain qualities which may include the properties of “higher strength, stiffness, lower weight to volume ratio,” economically efficient, appreciable durability, and eco-friendly characteristics. It should be adjustable as per the requirement of the patient and easy to cast as well. Polymer-based hybrid composite is one such material that comprises graphene and coir fiber as reinforcing material. Materials with higher performance, lightweight, and cost-effective benefits are of today’s need that can be incorporated in various applications such as aerospace, mechanical, and civil engineering domains [21]. Polymer-based composites are nowadays predominantly used and least expensive when

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compared to metals and ceramics. They are also chosen over metals as it provides higher strength and stiffness, low density, and good chemical resistance [28]. Polymer-based material includes epoxies, polyester, nylon, polycarbonates, polystyrene, etc. Both the reinforcing materials (graphene and coir fiber) have gained much popularity and attention due to their unique unmatched characteristics and remarkable option for designing the orthotic callipers [27, 30]. The fibers of graphene can be arranged layer by layer in a two-dimensional honeycomb lattice of carbon atoms. It was first isolated in the year 2004 as a material of the new generation. With the help of top and bottom down approaches graphene can be produced. the two derivatives of graphene such as graphene oxide (GO) and reduced graphene oxide (rGO) are derived from graphene. It is regarded as a superb material with beneficial and fascinating properties which can be used for manufacturing high-quality composites. These can be incorporated into various materials like polymers, ceramics, and metals in order to manufacture products that can exhibit electrically conductive and heat and pressure-resistant properties. It is also known as a “miracle material” as it is able to perform one or more than one function at a time spontaneously unlike other materials. It is lighter, strong, thin, large surface area, has higher electrical conductivity, and is hydrophilic. The production of graphene involves a ball milling process. The ball milling process increases the characteristics of filler materials that are embedded with polymeric blends and reduces the size of larger particles with the help of assembling molecules by allowing a change in filler structure. This process is environmentally friendly and economically efficient and possesses infinite applications in the domains of aerospace, packaging industries, transport and sports, pharmaceutical products, electronics, coatings, the making of electronic gadgets, etc. Graphene oxide is used for water purification purposes. Graphene’s inherent attributes opened up new and extraordinary opportunities which resulted in design of structures, building components which researchers never imagined. Composites are made up from matrix and fibers. Matrix can be made out of polymers, metals, and ceramics, whereas reinforcement can be short, long, and continuous and particulate type. In polymer when reinforcement is added it is termed composite and the final product made have properties different from individual components [12]. Matrix binds the fibers together and also helps in transferring the load to the fibers. It also helps in providing strength and rigidity to the fibers and slow the propagation of a crack. Fibers are reinforced in composites to enhance the mechanical properties and carry load in structural components [13]. Polymer matrix composites are least expensive when compared to metals and ceramics. They are most predominantly used due to high strength and stiffness, lighter in weight, less density and good chemical resistance [15]. They can be classified in two groups: thermoplast and thermoset composites. Thermoplastics are basically long chain of molecules with weaker bonds, when its heated it becomes soft and melts when heated above melting point [17]. Some of the examples of thermoplastic include polyethylene, nylon, polystyrene, acrylonitrile butadiene styrene, and polyphenylene

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sulfide. Thermosets consist of long chain of molecules with strong covalent bonds [13]. They can sustain higher temperature but they do melt beyond certain temperatures. Epoxies, polyimides, vinyl esters, polyester are some of the examples of thermoset. When we talk about the fabrication of thermoplast and thermoset composites some things are to be kept into consideration [33]. They both have different techniques and equipment to carry out their production process. So, in a good fabrication process there should be good adhesion between the matrix and the fibers so that air and porosity defects can be eliminated, and it should be easy to cast and inexpensive [22]. Thermosets can be fabricated by hand lay-up technique, one of the oldest techniques, or pultrusion, bag molding process, etc., are some of the processes known for production. To fabricate thermoplastic injection molding is popular [24]. Natural fibers are mainly extracted from plants (leaf, stem, root, seeds, etc.) and animals as well [19, 20]. When these are used as a reinforcement to produce a polymeric composite it results in higher strength to weight ratio, less costly and most important biodegradable. [5, 10]. If polymer matrix composites get reinforced with synthetic fibers (glass, carbon, and aramid) it leads to difficulty in disposal of the products manufactured and they are expensive too. Various polymers are reinforced with natural fibers such as kenaf, jute, hemp, flax, coir, wood, and jute [7, 9]. In the present work, the investigation has been carried out by reinforcing the graphene and coir fibers in epoxy (a polymer matrix) for preparing the composite that can be utilized in the side metallic callipers of orthotic callipers [35]. These side metallic callipers are mainly used by patients facing difficulty in gait movement and polio survivors [33].

2 Experimental 2.1 Materials In the current work, the graphene (2% by weight) and coir fibers (10% by weight) have been embedded with the epoxy (i.e., a polymeric matrix). The standard epoxy matrix consists of two components. One is “bisphenol AW 106” which acts as a resin and an “amine-based hardener HV 953IN [18].” Due to the cost-effectiveness, these thermosets have been taken into consideration for current work [1]. Also, the higher mechanical strength and high stiffness, high viscosity, less water absorbent characteristics, and relatively higher thermal stability made this a suitable choice for our work [4, 11, 16]. Graphene, which is titled as a “wonder material,” has astonishing properties. It is incredibly strong, a good conductor of heat and electricity, elastic in nature, thin, high strength and modulus, and flexible. GA when combined with other elements

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results in providing diverse applications. One can find its applications in batteries, solar cells, transistors, and water filtration [36]. Coir fiber is one of the naturally obtained fibers that are derived from coconut husk named under species Cocous nucifera [36]. It is thickest, resistant, and has a low decomposition rate which makes it one of the best options for manufacturing durable products [23, 26]. It inherits high strength, absorbs less water due to lower composition of cellulose content, and is less affected by wet conditions. It can be used for various applications including traditional furnishing materials, mats, farm tools, rope, and textile industries [25, 31].

2.2 Conditioning of the fiber Coir fibers that are obtained from the coconut plant take around one or more than a year to ripen. From one coconut tree, a person can take out 50–120 fruit each year. A fully matured tree of coconut consists of brown and white fibers. The brown/fibrous husk is soaked in water to make the fibers soft and swell and the white fibers are extracted by the retting process (bacteriological treatment of separating fibers) [37]. Then they are dried at a certain temperature for about 24 h. An important parameter for composite preparation is to test the functionality of the fiber and adhesion between the matrix and fiber, so analysis must be done after the fiber gets dried. “The untreated coconut fibers are pre-treated with alkaline solution 1% and again re-treated in vacuum filters and the coir fibers are washed with distilled water [2]. After doing all this treatment they are dried in an oven for 24 h at a temperature of 80° centigrade.” As per the supplier’s documentation, the specifications of graphene and coir fibers have been tabulated in Table 1 [2]. Table 1: Specifications of graphene and coir fiber (supplier data). Material

Specifications

Dimensions

Graphene

Diameter Purity Specific surface area Bulk density Oxygen content

– nm –% – m/g . g/cc % – microns . g/m .–. g/cc

As it is known that coir fibers possess a strong affinity for water absorption so they tend to spread over a wide area allowing easy mixture and resulting in better

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interfacial adhesion between the matrix and the fibre. Ultrasonication process was carried out in order to increase the adhesiveness property by mixing graphene (1%) + graphene + resin (1%) and hardener (1%) separately. To get good dispersion the mixture was kept in an ultrasonicator for about 1 hr. After that with the help of a mechanical stirrer the mixture was stirred at “100 rpm for 8–10 min” to develop a matrix. The obtained matrix was shifted into a rectangular metallic mold very slowly and carefully with coir fiber (10%). The proper orientation and spacing of fibers are one of the very essential aspects that must be taken into consideration. Further, the prepared composite was placed in “Carver Press” in order to suck the air bubbles at a temperature of 160 °C. The prepared composite samples were then allowed to rest for 5–6 h at room temperature for curing. For the post-curing purpose, the mold was afterward transferred to a hot air oven at 70 °C for 3 h. After the completion of the whole procedure, later the samples were taken for the investigation.

2.3 Material testing 2.3.1 Void assessment test Voids produce adverse effects on the applicability of composite materials in the application of engineered structures. The ASTM standard 2734-94 was used to conduct the void assessment test. The theoretical density can be determined using the basic “weight additive concept” and the actual density can be determined using Archimedes’ principle, which is the “water immersion approach.” The discrepancy between the actual and theoretical density is referred to as void, and it is measured in

Figure 2: Mettler Toledo electronic balance.

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percentages. In order to determine the acceptability of composites and the quantity of permitted void fraction, void evaluation is necessary.

2.3.2 Surface morphology The prepared specimen samples were then put under the scanning electron microscope (JSM-6390LV) for carrying out the microstructure of the prepared samples as shown in Figure 3. Before carrying out the microstructure, the platinum coating was done on the specimens. To avoid charging under the electron beam, the coating was done via plasma sputtering. The microstructure of the prepared composite samples was done for observing the distribution of nano-fillers as well as to check the nature and trend of the mechanical properties and the material behavior.

Figure 3: Scanning electron microscopy setup.

2.3.3 Mechanical tests Further, in order to analyze the mechanical behavior of the prepared samples, the tensile as well as the flexural tests were carried out. For fulfilling the purpose of testing, a universal testing machine (UTM) of 50 KN capacity, manufactured by Instron Limited as shown in Figure 4, was utilized as per the ASTM D 638 standards. For carrying out the investigation of the tensile test, rectangular-shaped prepared samples of dimension 63.5 × 10 × 3.2 mm having a gauge length of 7.65 mm were considered. The proposed experimentation was conducted at the “ambient temperature of 24 °C with a relative humidity of 56%.” Further, based on the three-point bending test, the flexural results were analyzed on the prepared sample of dimension 65 × 12.5 × 3.2 mm as per the flexural test standard of ASTM D 790-03.

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Figure 4: Instron universal testing machine.

3 Results and discussion 3.1 Void content Void formation during the manufacturing process is quite common and demands more attention as this influences the mechanical properties of the prepared composite materials; also, their performance gets diminished. The void formation is due to the entrapment of air bubbles during the composite processing techniques. In the present work, the prepared composite has been evaluated for the density (in gm/cc) and the void fraction (in %age) in the samples and the result obtained in this manner have been tabulated in Table 2. From given Table 1, it can be clearly stated that the obtained experimental value is less than the theoretical value which confirms the presence of voids in the prepared samples. “The behavior can be restated to the existence of air bubbles due to the adhesion of the fiber surfaces during the curing process.” Also, the density of epoxy-based composite is relatively less than that of the aluminum which ensures the “lower self-weight of the proposed orthotic callipers.” Table 2: Density and void content of composite and aluminum alloy. Material

Density(gm/cc)

Void fraction (%)

Experimental

Theoretical

Aluminum

.

–

Composite

.

.

.

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3.2 Morphological study The SEM image depicted in Figure 5 exhibits the “dispersion morphology and interactions between matrix and fiber.” The uniformly distributed contact between the fibers and the matrix may be seen in the illustration.

Figure 5: Image of scanning electron microscope.

3.3 Tensile and flexural tests According to ASTM D 638 standard, the tensile test was performed with sample specimens positioned between grips with a load capacity of 1 KN, a gauge length of 50 mm, and a crosshead speed of 2.5 mm/min. The data for tensile modulus and tensile strength are set into a computer that is connected to a machine configuration. Further, as per the ASTM D 790 standard, the flexural test was performed by loading the sample with a predetermined load until it fractured. For carrying out the mechanical tests, five test samples were tested for both aluminum and composite prepared. The average of the result was checked by determining the “standard deviation.” The plots for the different results have been depicted in Figures 6 and 7. In order to optimize the mechanical qualities, the fiber’s distribution with the epoxy matrix must be homogenous. At the interface, there should be a good “link between the fiber surface and the matrix.” It is obvious from SEM visualization that the distribution of the filler materials was uniform, and that the presence of graphene improved the adhesion between fibers and matrix. As a result, the primary bond formed at the interface between the fiber and the matrix aids in the transmission of load from the matrix to the fiber phase, resulting in the increased mechanical characteristics.

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Equivalent Stress (MPa)

Equivalent Strain

1200 1000 800 600 400 200 0

0.007 0.006 0.005 0.004 0.003 0.002 0.001 0 Aluminium

Composite

Aluminium

(a)

Composite

(b) Deformation (mm) 0.6 0.5 0.4 0.3 0.2 0.1 0 Aluminium

Composite

(c) Figure 6: Comparative study of tensile property and standard deviation for: (a) equivalent stresses; (b) equivalent strain deviations; (c) maximum deformation.

Equivalent Strain

Equivalent Stress (MPa) 5

3500 3000 2500 2000 1500 1000 500 0

4 3 2 1 0 Aluminium

Composite

Composite

Aluminium

(b)

(a) Deformation (mm) 6 5 4 3 2 1 0 Aluminium

Composite

(c) Figure 7: Comparative study of flexural property and standard deviation for: (a) equivalent stresses; (b) equivalent strain deviations; (c) maximum deformation.

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The flexural strength plot has been depicted in Figure 7. The depicted plots provide a clear indication of having higher strength of the prepared hybrid composite in the current work than that of the conventionally used aluminum alloy for orthotic callipers. The deformation and Von Mises strain characteristics for the prepared composite samples are found to be relatively less and the same is true for the tensile characteristics. Further, as depicted in the above plot, it is clear that the “maximum deformation and the strain also vary in a similar trend as in the case of equivalent von mises stress both under axial and lateral loading conditions.”

4 Conclusion The tremendous research that has gone with the view of developing non-traditional attractive materials with desired performance and desired mechanical characteristics has paved new ways and new opportunities for industries as well as researchers for the viable utilization of such natural fiber–based hybrid composites. In the present work, the development of such an attractive and hybrid composite has been carried out with the view to maximize the utilization of such hybrid (graphene- and coir fibers–based) composite instead of using the aluminum material in the “lower body orthotic callipers.” The present investigations found that the prepared hybrid composite of the said purpose exhibits excellent mechanical characteristics in terms of their tensile testing and flexural testing. The prepared composite samples possess higher strength and higher stiffness. The proposed work found “a lower weight to volume ratio” as compared to the traditional aluminum-based orthotic callipers. the present proposed work also suggests the utilization of such attractive composite materials for industrial and social benefits considering the view of sustainability and eco-friendly nature and costeffectiveness of such materials. “Hence, the usage of same would surely decrease the self-weight of the callipers and increase the mobility of polio survivors.”

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Mohan Kumar Pradhan, Shubham Gupta

Mechanical and wear properties of AL7075 Sic and graphite hybrid composite and optimization using utility additives method Abstract: Metal matrix composites (MMCs) are new-generation materials that are widely used for various advanced applications, namely, aerospace automotive thermal, structural, electronics, and owing to their superiority over the conventional materials. Their specific modulus, their specific strength, wear resistance, chemical inertness, high-temperature stability, regulated thermal expansion coefficient, etc. are much stronger. Among the several alternatives available, aluminum has to be the most widely used metal for matrix applications due to its lightweight and high strength. In this chapter, graphite and silicon carbide have been used as reinforcement in MMC aluminum. Graphite has a lubrication feature that reduces wear and friction when two surfaces slide over each other. It has a high resistance to corrosion, resulting in a long life of the components. Silicon carbide provides exceptional strength, hightemperature stability, oxidation resistance, and corrosion resistance. The effect of graphite and silicon carbide reinforcement on aluminum metal matrix composite has been analyzed. Aluminum hybrid composite with 5% Gr + 1% Sic and 5% Gr + 2% Sic has been manufactured using the stir casting method. A comparative investigation of the wear and mechanical properties of Aluminum 7075 alloys and hybrid composite alloys was conducted. Tensile strength in addition to hardness of the material has been acceded. The Taguchi orthogonal array was used for the experiment. The result of the wear test was then optimized using the utility additive method. The microstructure of the composite material SEM micrograph has been provided for analysis. Keywords: Aluminum 7075, EDM, ELECTRE method, machining, Taguchi method, mechanical property, Wear Property, utility additives method

1 Introduction The world is often searching for materials that do fit all sorts of challenges of service which has been determined on the basis to make observations on the basis of scientific analysis. This sustainability factor inspired many investigators to manufacture materials that met certain requirements historically unseen. In the modern environment, the bulk of products are used for a range of applications and their drawbacks have been shown. Mohan Kumar Pradhan, Shubham Gupta, Department of Mechanical Engineering, Maulana Azad National Institute of Technology, Bhopal https://doi.org/10.1515/9783110724684-007

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Almost all material was used for different practical applications, and their requirements have now been overcome. However, materials are needed in today’s world in hard conditions. This scenario calls for the origination of new materials from a variety of composite materials. This approach of developing new materials for specific application i.e. Novel materials with special characteristics that are customer-specific and distinct from their key materials can think up. This concept describes a set of material called composite materials that combine multiple forms of matrices with reinforcements that improve the properties. The desired requirements could not be met not just by matrices or the reinforcements but the composite material can have the same. And the desirable properties may be controlled as per the requirements by controlling the composition or maybe the method of fabrication or maybe the orientation, etc. This versatility in material processing allows the user to easily exactly monitor the manufacturing of composites with specific characteristics. It really has led to the advancement of superior mechanical and thermal properties of composite materials that have triggered their adoption into various fields of production. Three MMCs are applicable for structural mechanical aerospace automotive thermal and wear applications due to many advantages above other materials. Although these composite materials are mostly better than polymer Matrix composites (PMCs) in terms of specific modules, specific strength wear resistance, chemical inertia, stability at high temperatures, precise thermal expansion coefficient, etc. But MMCs still have greater transverse stiffness and strength compared to PMCs’ shear strength and flexibility at high temperatures. The advantageous physical properties are high electrical and thermal conductivity, no absorption of moisture, low flammability, and resilience to most radiations. Compositionally the MMCs have at least two components, i.e., the matrix and the reinforcement the matrix is usually metal but often pure and in certain contexts, it is essentially alloyed. The most widely used alloys were mostly based on aluminum and titanium. Both materials (aluminum and titanium) have a low density as being easily come in a wide variety of alloy concentrations Other alloys can be used in some distinct instances since they have their advantages and disadvantages, namely: Beryllium is the lightest of all building materials consisting of a tensile strength significantly larger than that of steel but it may be highly brittle, thus reducing the availability for a specific use. Magnesium is light but has high reactivity to oxygen. Superalloys based on nickel and cobalt were used in some situations and most of the alloy elements used in the superalloys have been shown to have an adverse impact on the strengthening of fibers at high temperatures.

2 Composite materials A composite is a combination of two or more materials blended on a macroscopic level and is ordinarily formed of reinforcement such as fibers, flakes fillers, or

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particles rooted in a matrix such as ceramics, polymers, and metals. The matrix supports reinforcement to provide the necessary form material, which enhances the mechanical and thermal characteristics of the reinforcing matrix. The newly designed material has the proper design and improves its strength on a standard basis [16]. Many materials, such as metals, doped ceramics, polymers, and alloys mix up along with additives and also have dispersed phases in their structure in small quantities. Nevertheless, they are not considered composites since they have the same properties as the basic component. Substantial tensile strength, stiffness, reduced density, superior electrical and thermal conductivity, a reasonable coefficient of friction, thermostability at elevated temperature, corrosion resistance and resistance against wear, and so on are needed characters of composite materials. These materials serve multiple functions and provide qualities and characteristics that a single element cannot provide. Even though the materials used to make composite materials differ in composition and shape, they must be compatible [17].

3 Classification of composite Composite materials are categorized in two different manners based on: 1. Matrix of the material 2. Shape of reinforcement

3.1 Based on matrix material 3.1.1 Metal matrix composite Metal matrix composites (MMC), like all composite materials, form a minimal pair of chemically and physically discrete phases, which are not uniformly transmitted to offer similar properties. Typically, they are two phases, e.g. a particle or fibrous phase metallic structure. A metal matrix composite (MMC) is made up of two constituent elements: a metallic base and a reinforcing ingredient that is often non-metallic and ceramic. The manufacturing method for MMCs is, by definition, distinct from that of ordinary metal alloying. MMCs are frequently created by mixing two elements, as opposed to their polymer matrix equivalents (e.g., a metal as well as a ceramic fiber). Popular MMC kinds are: Aluminum matrix composites (AMC) Magnesium matrix composite (MMC) Titanium matrix composite (TMC) Copper matrix composites (CMC)

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Among the various metallic alloys, aluminum alloys are a lot frequently utilized as a matrix in metal matrix composites. Al alloys have been extensively used due to the advantageous characteristics, which include lower value of density, high resistance against corrosion, enhanced thermal in addition to electrical conductivity, and increased precipitation intensity, besides high damping capability. Al alloys have been widely used due to their advantageous properties. Al matrix composites (AMCs) have been used in many products, namely, sporting goods, military equipment, electronic packaging, and automotive applications. It has a vast diversity of mechanical properties that depend upon the chemical composition of aluminum matrix. Matrix are generally reinforced by alumina (Al2O3), SiC, and C. For the producing of the aluminum metal matrix composite, diffident processes like stir casting, squeeze casting, and powder metallurgy, have been frequently utilized.

3.1.2 Ceramic matrix composite Ceramic matrix composites are generally made up of a ceramic substrate coupled with specific ceramic materials in the structure’s dispersion process. Because normal ceramics are exceedingly brittle, ceramic matrix composites have greater toughness than ordinary ceramics. CMCs are often reinforced with either longer or continuous fibers or even shorter closed fibers. Traditional processes are used to make short-fiber (discontinuous) reinforced ceramic composites, which typically consist of an oxide (alumina) as well as silicon-oxide (SiC) ceramic matrix reinforced with whiskers of SiC, zirconium oxide (ZrO2), titanium boride (TiB2), aluminum nitride, as well as different ceramic fibers. Because of their higher stiffness and strength, Sic fibers are commonly used to strengthen ceramic-metal composites. Whiskers placed in short fibers improve the staying power and fracture propagation resistance of ceramic matrix composites. Short-fiber reinforced fiber, on the other hand, is prone to failure. Long monofilament or long multifilament fibers are embedded in long fiber reinforced ceramic composites. In dispersed form, continuous monofilament fiber has a greater strengthening effect. This is created using the chemical vapor deposition (CVD) of Sic on the tungsten and perhaps carbon fiber substrate. Monofilament fibers offer a strong interface connection to the matrix, which boosts durability.

3.1.3 Polymer matrix composite PMC materials are made by combining the polymer resin matrix along with the fiber reinforced dispersion. Polymer-based composites are quite common due to their cheaper costs and ease of production. Unreinforced polymers are limited in their mechanical properties as structural materials, namely: The tensile strength of

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some of its toughest resins in polymer epoxy is 20000 psi 140 MPa. Aside from comparatively lower strength, polymers also have lower impact resistance too.

3.2 The form of reinforcement 3.2.1 Particulate composite They may be categorized as: 1. Particulate composites having constituents that are randomly orientated. 2. Composite materials with the specified particle configuration. The materials’ dispersed phase consists of two-dimensional flat flakes that are parallel. The influence of dissipated particles on the characteristics of composites is governed by the scale of the elements. Fine particles ( E5 > E4 > E2 > E6 > E8 > E3 > E7 > E1

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8 Result and discussion 8.1 Influence of wear parameters on rate of wear as well as COF The rate of wear as well as the coefficient of friction is collected from the Pin on Disk machine as revealed in Table 7. Table 7: Parameters of wear testing and wear characteristics. Exp. no.

Graphite addition (%)

Normal load (N)

Sliding speed (m/s)

Wear rate (mm/min)







.

.

.







.

.

.







.

.

.







.

.

.







.

.

.







.

.

.







.

.

.







.

.

.







.

.

.

COF

8.1.1 Wear rate The main effect plots normal load sliding speed and weight % of Gr have been depicted in Figure 17; it can be apparent from the figure that with the increase of normal load wear rate decreases; however, it increases with rise in sliding speed and wt% of Gr. Figure 17 depicts the influence of Gr(wt%), normal load, along with the sliding speed on rate of wear. It would seem that the value of Gr (wt%) increased. The wear rate is growing sharply and reaches to the maximum wear rate when the (wt%) of graphite at maximum, i.e., at 2%. Apart from this, it does seem that the rate of wear is also increasing with a sliding speed similar to that of wt%, It reaches its maximum value when the parametric range of the sliding speed is 1.00 m/s with the parametric range. Nonetheless, as the normal load (N) increases, the wear rate decreases to a minimum of 120 N. The main effect plot of the rate of wear may be depicted in Figure 17.

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Main Effects Plot for SN ratios Data Means Sliding speed, m/s

Normal load, N 14 12

Mean of SNratios

10 8 6 40

80 Gr addition, wt.%

120

0.25

0.50

1.00

14 12 10 8 6 0

1

2

Figure 17: Main effect plot for wear rate.

8.1.2 On coefficient of friction For analysis of means and S/N relationships, the Taguchi method has been adopted; it is a method that involves pulling out special effects and visually incorporating significant effects of different significant factors Figure 18 illustrates the S/N ratio for the wear behavior to estimate their impact on the estimated responses. The influence of Gr (wt%), normal load, as well as sliding speed on COF is shown in Figure 18. The figure reveals that, as the Gr(wt%) level goes up, COF also increases. As a result, the greatest wear loss arises at the greatest (wt%) of graphite, i.e., at the limit of 2%. When the level of sliding speed raises, so does the COF. According to the graph, the COF achieves a maximum value of 1.00 m/s. In addition, when the amount of normal load (N) increases, COF drops and reaches its lowest at 120 N.

8.2 Optimization of wear parameters To obtain the best set of the wear parameters to decrease the wear rate of the composite, an AHP-based utility additive technique was embraced for the optimizing of the wear parameters for wear rate of the hybrid composite (Al7075 + 5%SiC + 1%Gr), (Al7075 + 5%SiC + 2%Gr) and Al 7075 alloy and to hit the rank of options available.

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Main Effects Plot for SN ratios Data Means Sliding speed, m/s

Normal load, N

22 21

Mean of SNratios

20 19 18 40

80

120

0.25

0.50

1.00

Gr addition, wt.%

22 21 20 19 18 0

1

2

Figure 18: Main effect plot for COF.

Option 9 is in the first position, and option 1 occupies the last, and consequently, the result shows that the most appropriate choice is alternative 9.

9 Conclusion In this research, the wear property of the hybrid composite (Al7075 + SiC + Gr) using Pin on Disk setup as well as the impact of wear attributes on wear rate, as well as COF in a hybrid composite has been studied. The experiments have been performed with different parametric settings of graphite wt%, sliding speed, and normal load. The best option was chosen by the AHP and the utility additive method. The popular Minitab 18 software was utilized for designing the experiments using the Taguchi method. The influence of wear parameters on the output was analyzed and experimentally validated. The findings show that the rate of wear is directly influenced by the of Gr(wt%), reaches the maximum at the highest (wt%) of graphite, i.e. at 2%. Similarly, it increases with the sliding speed also, and the wear rate reaches a maximum value of 1.00 m/s. B However, when the value of the normal load (N) increases, the wear rate falls and attains the lower limit of 120 N. Consequently, with the increase in the value of Gr (wt%), COF also increases and reaches the maximum wear rate. It is now at the utmost (wt%) of graphite, i.e., about 2%. The COF also increases whenever the sliding speed rises and attains a maximum value of 1.00 m/s. Furthermore,

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when the magnitude of the normal load (N) increases, the COF drops until it reaches a minimum of 120 N. In the end, the parametric optimization of wear with the AHP has been performed, the normalized weight of attributes, namely, wear rate and COF, have been calculated, and the utility additive method has been employed to the ranking of the alternatives. The ninth alternative is found to be the best option, followed by the fifth alternative, which makes them the most preferable option for wear testing of the hybrid composite.

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Subject index aerospace 81 ageing 43, 47 aluminium 10 Aluminum 103–104, 110, 117, 118, 119–120, 133–134, 136 applications 3, 5, 43, 55, 62 automotive 81

metal matrix composites 11, 117, 128, 133 microscopy 23 MMC 11, 117, 119, 124, 134 polymer 14, 43, 81–82, 103–105, 118, 120 polymer matrix 103, 118, 120 POSS 7, 14, 23, 25–37 processing 3, 5

bidirectional 74 carbon fiber 81, 83 CF 14, 16 CFD 81–82, 84–85, 87 characterization 3, 5, 23, 27 CNTs 23–35, 37 coir fibers 103 composite materials 81–82 corrosion 133 epoxy resin 67, 81 flexural modulus 59, 72–73 flexural test 72, 103, 111 friction 16, 46, 48–50 FSI 81–85, 88–89, 93, 99 glass fiber 81–82 graphene 15–16, 103, 105–107 Graphite 117, 133–134, 136, 139, 145, 147 hardness 12, 134–136 hybrid composites 3, 15–16

reinforced hybrid composites 14–15 RH 59–61, 66–67, 69, 71–72, 76 rice husk 59, 66 rice straw 59, 66 RS 59–62, 67, 69–70, 72–74, 76 RS–RH 59–60, 62, 67, 69–70, 72–74, 76 SiC 11–12, 15, 120, 134–135, 138, 146–147 silicon carbide 117, 133–134 single layer 74 sliding contact 43, 55 sonochemical coatings 23 spectroscopy 23, 31–32 stir casting method 134 structural 14, 87 tensile test 70, 74–75, 103 thermal 6, 14–15, 26, 29, 37 unidirectional 70 utility additive method 117, 141 vehicles 81 viscoelasticity 53, 55

impact load 81, 83 Kevlar 10, 12, 15, 81–83, 93, 97 locomotive 81

https://doi.org/10.1515/9783110724684-008

wear 15–16, 54, 117, 131–134, 136–137, 139–140, 142, 145, 148