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metal-matrix fiber-reinforced composites, there are important unresolved questions regarding the i n t e r a c t i o n of the c o m p o n e n t s d u r i n g s t r a i n i n g and a m a t r i x b e h a v i o r d i f f e r e n t f r o m that of the unr e i n f o r c e d m a t r i x m a t e r i a l . E f f e c t i v e e x a m i n a t i o n of these questions requires direct structure observations in a d d i t i o n to m e c h a n i c a l t e s t s . T h e a u t h o r s have s t u d i e d c o m p o s i t e s of t u n g s t e n w i r e s in a c o p p e r s i n g l e - c r y s t a l m a t r i x and r e p o r t e d e t c h - p i t s t u d i e s of the e n h a n c e d d i s l o c a t i o n d e n s i t i e s p r o d u c e d in the m a t r i x d u r i n g p r e p a r a t i o n a s a r e s u l t of d i f f e r e n t i a l s h r i n k a g e a f t e r s o l i d i f i c a t i o n . 1 T h i s p a p e r d e s c r i b e s the b e h a v i o r of t h e s e c o m p o s i t e s d u r i n g d e f o r m a t i o n at r o o m t e m p e r a t u r e . A s a m o d e l s y s t e m , C u - W is a t t r a c t i v e f o r i t s r e l a t i v e e a s e of f a b r i c a t i o n with d i f f e r e n t f i b e r d i a m e t e r s and s p a c i n g s by s e v e r a l m e t h o d s and f o r the a b s e n c e of i n t e r f a c e and a l l o y i n g p r o b l e m s . S e v e r a l s t u d i e s c o n c e r n e d with the q u e s t i o n of f i b e r m a t r i x i n t e r a c t i o n have b e e n m a d e , 2"4 A l l found d e r i v e d m a t r i x flow s t r e s s e s m u c h g r e a t e r than that of i s o l a t e d c o p p e r . K e l l y and L i l h o l t ~ c o n s i d e r e d this due to p l a s t i c c o n s t r a i n t in a s h e l l s u r r o u n d i n g the f i b e r a r i s i n g f r o m the P o i s s o n ' s r a t i o d i f f e r e n c e b e t w e e n e l a s t i c f i b e r and p l a s t i c m a t r i x . L e e and H a r r i s 3 r e g a r d e d this effect a s m i n o r a t m o s t . T h e y found m a t r i x g r a i n s i z e to v a r y with f i b e r s p a c i n g b u t s u g g e s t e d that m a t r i x s t r e n g t h e n i n g was m o r e d i r e c t l y r e l a t e d to a p o s t u l a t e d d i s l o c a t i o n s u b s t r u c t u r e within the g r a i n s a s h o t - p r e s s e d , Hughes and R u t h e r f o r d 5 had e a r l i e r i n t e r p r e t e d s t r e s s - s t r a i n c u r v e s of i n f i l t r a t e d C u - W c o m p o s i t e s by p o s t u l a t i n g that in the a s - p r e p a r e d c o m p o s i t e t h e r e was a m a t r i x r e g i o n of high d i s l o c a t i o n d e n s i t y s u r r o u n d i n g e a c h f i b e r , but they did not t e s t t h e i r f i b e r s and did not p r e s e n t d e r i v e d m a t r i x c u r v e s . None of t h e s e s t u d i e s included o b s e r v a t i o n s of d i s l o c a t i o n s t r u c t u r e . To e n a b l e t h e s e to be m a d e in the p r e s e n t work, it was n e c e s s a r y to use large interfiber spacings. EXPERIMENTAL The 3.2 m m d i a m • 38 m m