A summary of pyrotechnic shock in the aerospace industry

NASA Technical Documents, 1970. — 7 p.Pyrotechnic shock data have been obtained from a survey of the aerospace industry

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A summary of pyrotechnic shock in the aerospace industry

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A SU"AKY OF PYROTECHNIC SHOCK I N T1tE AEUOSPACE IhQUSTRY

W. P. Rader HarLin M a r i e t t a Corporation Denver, Colorado and William F. Bangs Goddard Space F l i g h t Center G r e e n b e l t , Waryland Pyrotechnic shock d a t a have been obtained from a survey of t h e aerospace i n d u s t r y and government agencies. Over 2800 measurements from 30 c o n t r i b u t o r s have been comp i l e d and c a t e g o r i z e d according to type o f p y r o t e c h n i c d e v i c e and s t r u c t u r e . These d a t a were analyzed t o provide a reference. document and e s t a b l i s h g u i d e l i n e s f o r des i g n i n g and t e s t i n g t o t h e pyrotechnic shock environment. T h i s paper p r e s e n t s a summary of t h e t o t a l program and a d i s c u s s i o n of pyrotechnic test s i m u l a t i o n techniques. F u r t h e r r e s u l t s from t h e s t u d y , i n c l u d i n g g u i d e l i n e s f o r design and f o r p r e d i c t i n g shock environments, a r e presented i n a paper by Dr. Plichael B. WcGrath, e n t i t l e d "A Discussion of P y r o t e c h n i c Shock Criteria" d u r i n g t h e 4 1 s t Shock and V i b r a t i o n Synlposium.

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INTRODUCTION

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Pyrotechnic shock is perhaps t h e l e a s t understood of t h e dynamic environments a s s o c i a t e d with t h e o p e r a t i o n of aerospace v e h i c l e s and components. To d a t e , t h e problem of p r e d i c t i n g or even adequately e x p l a i n i n g pyrotechnic shock h a s d e f i e d s o l u t i o n by r i g o r o u s mathematical t r e a t m e n t s . P r e d i c t i o n of t h e environment and t e s t i n g techniques a r e c u r r e n t l y based primarily on e m p i r i c a l uethods. Recent observations showed t h a t r e l i a b l e d a t a were widely s c a t t e r e d among many companies and a g e n c i e s , and t h a t t e s t i n g technology was n o t openly discussed between o r g a n i z a t i o n s . T h e r e f o r e , t h e Goddard Space F l i g h t Center, r e c o g n i z i n g t h a t a l a r g e amount of d a t a B x i s t e d i n the i n d u s t r y , sponsored a program t o c o l l e c t and c a t e g o r i z e t h e s e d a t a and e s t a b l i s h g u i d e l i n e s f o r designinp structure and equipment t o t h e pyrotechnic shock environment. T h e s t u d y was performed by t h e X a r t i n M a r i e t t a c o r p o r a t i o n under C o n t r a c t s h'AS5-15208 and NASS-21241.

I?.

Recommendation of measurement systems f o r ground test and f l i g h t .

E.

fin

3 .

e t

m.

F. Recommendation of test sirnulati techniques. G.

C l a s s i f i c a t i o n of p y r o t e c h n i c systems according t o t h e n a t u r e of r e s u l t i n g shock and damaging e f f e c t s

H.

Evaluation of e f f e c t s of s t r u c t u r a l c o n f i g u r a t i o n s and m a t e r i a l s on reSUI t i n g shock c h a r a c t e r i s t i c s .

I.

Formulation of a follow-on r e s e a r c h program.

J.

A p p l i c a t i o n of shock propagation theo r y t o a t l e a s t one c l a s s of pyrotechn i c s y s t e m s compiled i n t a s k C and comparison of r e s u l t s w i t h measured data.

.

Compilation of "reduccd" pyrotechnic shock d a t a r e p r e s e n t a L i v e of aerospace s y s tems

.

B.

.

Evaluation of t h e " q u a l i t y " of t y p i c a l l y a v a i l a b l e pyrotechnic shock d a t a .

The s p e c i f i c (asks performed i n the c o u r s e of t h e program were: A.

--

C.

.

K.

D e f i n i t i o n of d i s t i n c t i v e c h a r a c t e r i s -

Perforirwnce of a ground t e s t program uslng f u l l s c a l e l i t a n 111 s t r u c t u r e to provide s p e c i f i c i n f o r r a t i o n t h a t w i l l a i d i n t h e understanding of b a s i c p y r o t k l i n i r shock t r a n s i e n t phcnor.ena

.

-

9

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I

I

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L,

zyxwvutsrqponm zyxwvutsrq zyxwvutsrqp is r a p i d l y a t t e n u a t e d , and s t r u c t u r a l resonances begin t o c o n t r o l t h e shock spectrum. The e f f e c t is i l l u s t r a t e d by t h e shock s p e c t r a i n F i g . 1. I t should be recognized t h a t a c c e l e r o n c t e r . i n s t a l l a t i o n s can s e r i o u s l y i n f l u e n c e t h e ncasurcd d a t a , p a r t i c u l a r l y a t l o c a t i o n s near t h e shock source. The e f f e c t on t r a n s ducer resonance frequency of s e v e r a l mounting i n s t a l l a t i o n s has been i n v e s t i g a t e d by Rasanen [ 2 ] . T h i s work i n d i c a t e d t h a t t h e use of a l u minum blocks f o r accelerometer i n s t a l l a t i o n s could l o v e r t h e mounted resonance frequency by a f a c t o r of 2 t o 3 from t h e t r a n s d u c e r resonance s p e c i f i e d by t h e manufacturer.

Invcstijintion of t h e e f f e c t s of mass loading on t h e pyrotechnic shock environment.

A c o z p l e t e d e s c r i p t i o n of each of these tasks and the r e s u l t s have been published i n a s i x volune r e p o r t [ I ] . This paper p r c s c n t s a b r i e f d e s c r i p t i o n of r e s u l t s of s e l c c t e d tasks with emphasis on t e s t s i m u l a t i o n of pyrotechnic elwck.

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DATA CO?1PlLATLOX k ! D CATEGOKIZATIOX

Over 2800 pyrotechnic shock measurements were ronpilcd and c a t e g o r i z e d according to the t y p e of device and type of s t r u c t u r e thrcugh uliich t!ie shocks propagated gs l i s t e d i n Table 1. Each wasuremcnt is presented i n PlCR-69611 [ l ) showing the a c c e l e r a t i o n t i m e h i s t o z y , t h e shock spectrum ( u s i n g a s t a n d a r d format w i t h an a n a l y s i s Q of 10 f o r most cases} ana a drawing showing s t r u c t u r a l c o n f i g u r a t i o n i n cluding t h e l o c a t i o n s of t h e pyrotechnic device and LIIC transducers.

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Table 1. O u t l i n e o f Data C l a s s i f i c a t i o n A.

1.

C.

S t r u c t u r e c u t t i n g charges (mild d e t o n a t i n g fur;c?, f l e x i b l e l i n e a r shaped charge, primchord. etc.} 1.

Skin-ring-frame

2.

Truss structure

3.

Other s t r u c t u r e

structure

Explosive n u t s and b o l t s

1.

Skin-ring-frame s t r u c t u r e

2.

-Truss s L r u c t u r e

3.

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C a r t r i d g e a c t u a t e d devices (pin p u l l e r s , b o l t cutters, cable c u t t e r s , etc.)

1.

Skin-ring-frame

2.

Truss s t r u c t u r e

3.

Other s t r u c t u r e

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structure

U.

Space Vehicle test d a t a

E.

f l i g h t measurements

rrrqueary I 0.1 (US)

Fig. 1

- Comparison of

shock s p e c t r a a t v a r i o u s propagation d i s t a n c e s

CtUUCTERISTICS OF PYROTECHNIC SHOCK TRANSIENTS

DAMAGE EFFECTS The compiled pyrotechnic shock d a t a were used t c determine d i s t i n c t i v e c h a r a c t e r i s t i c s of t h e shock t r a n s i e n t s i n c l u d i n g propagation v e l o c i t y , frequency c o n t e n t , and a t t e n u a t i o n of m p l i t u d e w i t h d i s t a n c e .

Information concerning damage e f f e c t s rel a t e d t o shock amplitude is extremely l i m i t e d because of l a c k of documented f i i l u r e h i s t o ries. One of t h e p e r p l e x i n g a s p e c t s of t h i s s t u d y was t h a t i n s p i t e of t h e magnitude of t h e survey and t h e response i n c o n t r i b u t i o n of d a t a , only 29 miscellaneous anomalies and 17 cases of r e l a y c h a t t e r were r e p o r t e d . As a r e s u l t , methods f o r r e l a t i n g pyrotechnic shock damage p o t e n t i a l w i t h s t r u c t u r e and equiprcent f r a g i l i t y l e v e l s do not e x i s t , although some p r e l i m i n a r y i n f o r m a t i o n i n d i c a t e s shock veloci t y may be a s i g n i f i c a n t parameter.

The propagation v e l o c i t y was measured f o r s e v e r a l d i f f e r e n t s t r u c t u r e s . V e l o c i t i e s corresponding t o both compressional and s h e a r yaves were found t o erist i n t h e measured data. !;ear t h e shock source, t h e a c c e l e r a t i o n t i n e histories a r e c h a r a c t e r i z e d by high amplitude, high frequency conplex waves. As t h e d i s t a n c e between t h e shock s o u r c e and t h e measurenent l o c a t i o n i n c r e a s e s , t h e high frequency energy

10

.

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Generally, s t r u c t u r a l failures a r e confinctl t o s m a l l f i t t i n g s , b r a c k e t s , bonds, and c l e c t r i c a l connectors t o s m a l l corrponcnts s u c ! ~as d i o d e s and t r a n s i s t o r s . Most damage e f i c c t s are s e e n i n cquipriciit m l f u n c t i o l r such ns cltatt e r o r t r a i i s f e r o i r c l d y s and switches, [requency s h i f t i n s u b c a r r i e r o s c i l l a t o r s , and t r a n s i e n t s induced i n s i g n a l outputs. Llsually, t h e d e s i g n d e f i c i e n c y or workmanship problem is q u i t e simple t o c o r r e c t . T h i s c h a r a c t e r i s t i c may make t h e anomalies appear i n s i g n i f f c a n t , e s p e c i a l l y i n t h e d e v e l o p m n t p l m s e , and may p a r t i a l l y e x p l a i n t h e small number of rep o r t e d problems. TEST SINULATION

.

Photograplis of the f o u r configuratioiis .ire sliown i n Fig. 2-5. Accclerornctcr l o r n t i c ~ n son Lhc payload t r u s s 3re shown in Fig. C . i:x;in,plcs of thc average shock spectra o h t a i i w d a t l o c a t i o n s 7-and 8 ( s n t ~ * l l i t mounting c points) for the four d i f f e r c n t configuraLiuiis a r t - s l i c w n i n b i g . 7 and 8. Comparison or tlicsc d a t a indic.itcs t h a t t h e use o f t h e simple clianiicl a d a p t e r s t o s i m u l a t e the t r a n s t a g e s k i r t s t r u c t u r e would provide a reasonable, c o n s e r v a t i v e t e s t of t h e s a t c l l i t e . The r e s u l t s , although i n c o n c l u s i v e , a r e encoura g i n g bccausc they i n d i c a t e that i t m y iiot be necessary to always i n c l u d e an expensive. complex s t r u c t u r e i n f u l l s c a l e testing. (
lie of basic annlysis actually clouds the issue rather than clarifies it.

. nttcniialion

.

nIr. %ell: The various analysis methods for clctcniiining structural properties such as mcchanic d inipcd:mcc and trmsniissibility as .a function of fi-ecluency, cannot tic applied directly to a shock spectrum in data that is gciierxlly acquircd i n the coursc of a dcvclopnicnt and test program on a particular structure. ~

-

-

gcst ing that tlic shock spectrum sliowcd :in additional characteristic at tlic lo\v frcqucncy end which tcndcd to bc niorc of a coilstant displ:iccmcnt typc of behavior, and l noticed that porhxps this was present i n sonic of your CUI'VCR. It i s iiiiportant I think to

know uhrrc. the constant sclocity linc is likcly to beconic innpplicnblc at thc low frcclucncy cnd. Do you have a short obscrvatioii on that?

hlr. hlcCr@: Wc werc in corrcspondence with Bill Rol>cils nntl wc loolied for this characteristic of a constail displncciiirnt linc at n very low frcriucncy, but quite oftcn the> data confuses thr issuo at very low frcquencics bcc;msc of faulty tccliniyucs of obtaining Ihc spectrum. We found that thu constant accclcrdion lincs, constant velocity lines, constant displsceiiient, just did not lead to any dclinitc results that we could scc. Thc constant velocity lincs that WP are referring to arc almost a sulijcctivc approximation in the low frrclucncy rangc, which wight go from approximatclp 100 IIz up to RS high as a thousand Iiz. This is what wc obscrscd. Soincone else might obscrve sonicthing else, but it probably takes a spccific type of a data reduction.

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Nr. Radcr: During the eoursc of this program one of ihc tasks was a coinparison of Fouricr spcctrn V C ~ S I I Sstandard shock spectra. Thc Fouricr spectra gavc csscntially no more information than the shock spectra for the complcs waves that arc gcncrated by pyrotechnic shock dcviccs. This is not true for siniplc !xrlscs since thc I~ourierand the shock spectra can hc quite different. But for the* complex waves that one sees i n typical pyrotechnic shock tlcviccs tlir Fourirr and shock spectra yirltlctl cssentially thc same infornintion in our espcricnr*c.

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