The effect of thermal history on the axial tensile behavior of an aligned fiber composite
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xt t h e r m a l l y - c y c l e d by i m m e r s i n g in the b o i l i n g w a t e r (100~ and the liquid n i t r o g e n ( - 196~ a l t e r n a t e l y . The n u m b e r of c y c l e s was one hundred. The thermally-cycled specimens were finally subjected to an a d d i t i o n a l t e m p e r a t u r e change of e i t h e r r o o m t e m p e r a t u r e (RT) ~ - 196~ ~ R T o r R T ~ 300~ RT. (The t r e a t m e n t s ' R T ~ - 196~ ~ R T ' and ' R T - - 300~ ~ R T ' a r e h e n c e f o r t h d e s i g n a t e d as ' t y p e A ' and ' t y p e B ' t r e a t m e n t s , r e s p e c t i v e l y . ) All t e n s i l e t e s t i n g w a s p e r f o r m e d at r o o m t e m p e r a t u r e in an I n s t r o n m a c h i n e a t a c r o s s h e a d s p e e d of 0.1 m m / m i n . S p e c i m e n s w e r e held d i r e c t l y in s p l i t g r i p s having a gage length of 40 m m . The t e n s i l e load was a p p l i e d in the f i b e r d i r e c t i o n up to a t e n s i l e s t r a i n of 0.2 p c t in a l l c a s e s . F o r a c c u r a t e m e a s u r e m e n t s of t e n s i l e s t r a i n s , s t r a i n g a g e s w e r e a t t a c h e d to the b r o a d f a c e s of the t e n s i l e s p e c i m e n s ; the s t r e s s s t r a i n c u r v e s w e r e r e c o r d e d c o n t i n u o u s l y b y an x - y recorder. The t h e r m a l e x p a n s i o n b e h a v i o r of the s p e c i m e n s with 9.5 vol p c t tungsten w i r e s was e x a m i n e d in a t e m p e r a t u r e r a n g e b e t w e e n r o o m t e m p e r a t u r e and 800~ Length c h a n g e s in the f i b e r d i r e c t i o n alone w e r e m e a s u r e d u s i n g a q u a r t z tube d i l a t o m e t e r . D e t a i l s of the m e t h o d a r e given e l s e w h e r e . ~ A r a t e of t e m p e r a t u r e change d u r i n g the t e s t s was 200~ E X P E R I M E N T A L RESULTS F i g s . 2(a) and (b) show the a x i a l t h e r m a l e x p a n s i o n b e h a v i o r of the 9.5 vot p c t a l i g n e d t u n g s t e n f i b e r c o p p e r c o m p o s i t e . In the f i g u r e s , a s e r i e s of n u m b e r s f r o m ' 1 ' through '14' i n d i c a t e s the path of the e x p a n s i o n / c o n t r a c t i o n c u r v e s . At ' 1 ' in F i g . 2(a) and '11' i n F i g . 2(b ), the c o m p o s i t e was h e l d for 5 h. Between '~" in F i g . 2(a) and ' 5 ' in F i g . 2(b), the t h e r m a l - c y c l e (TC) t r e a t m e n t ( - 196~ ~ 100~ 100 c y c l e s ) f o l lowed b y the type A t r e a t m e n t (RT ~ - 196~ ~ RT) was p e r f o r m e d . It can be s e e n c l e a r l y f r o m the f i g u r e s that the e x p a n s i o n / c o n t r a c t i o n b e h a v i o r of the c o m p o s i t e is not r e v e r s i b l e ( e . g . , ' 2 - 3 - 4 ' in F i g . 2(a) and ' 5 - 6 - 7 ' in F i g . 2(b)). This i s due to p l a s t i c a c c o m m o d a t i o n to t h e r m a l e x p a n s i o n m i s m a t c h , a s shown p r e v i o u s l y . 2 H e r e the following should b e noted: VOLUME 6A, SEPTEMBER 1975-1755
Fig, 1--A typical scanning e l e c t r o n m i c
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