Creep behavior of fiber reinforced metal matrix composites
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AND
A. S. YUE
A t h e o r e t i c a l m o d e l of the c r e e p b e h a v i o r of m e t a l m a t r i x c o m p o s i t e s having s t r o n g f i b e r - m a t r i x i n t e r f a c e s is d e s c r i b e d in t e r m s of creep p a r a m e t e r s of the m a t r i x and f i b e r s . The a v a i l a b l e e x p e r i m e n t a l data, obtained from the u n i d i r e c t i o n a l l y solidified a l u m i n u m - n i c k e l eutectic containing 10 vol pct A13Ni f i b e r s , a r e in good a g r e e m e n t with the t h e o r e t i c a l m o d e l . The c r e e p a c t i v a t i o n e n e r g y of the c o m p o s i t e is d e s c r i b e d in t e r m s of the c r e e p a c t i v a t i o n e n e r g y of f i b e r s and the m a t r i x . The e x p e r i m e n t a l l y det e r m i n e d data of (Co, Cr)-(Co, Cr)TC~ and A1-A13Ni e u t e c t i c s a r e in a g r e e m e n t with t h o s e v a l u e s as p r e d i c t e d .
F I B E R - R E I N F O R C E D m e t a l m a t r i x c o m p o s i t e s and c o m p o s i t e s produced by the u n i d i r e c t i o n a l l y e u t e c t i c s o l i d i f i c a t i o n technique ~ a r e c o n s i d e r e d as p o t e n t i a l s t r u c t u r a l m a t e r i a l s for high t e m p e r a t u r e a p p l i c a t i o n s b e c a u s e these c o m p o s i t e s have slow d e f o r m a t i o n r a t e s and e x c e l l e n t m i c r o s t r u c t u r a l s t a b i l i t y 2'3 at e l e v a t e d t e m p e r a t u r e s . In spite of these a d v a n t a g e s , the c r e e p b e h a v i o r of t h e s e m a t e r i a l s a r e not s u f f i c i e n t l y u n d e r s t o o d . R e c e n t l y , t h e r e have b e e n s e v e r a l t h e o r e t i c a l d e s c r i p t i o n s 4-1~ of the c r e e p b e h a v i o r of m e t a l m a t r i x c o m p o s i t e s , but most of these a n a l y s e s have been confined to the s t e a d y - s t a t e c r e e p b e h a v i o r . At p r e s e n t , t h e r e has b e e n v e r y few t h e o r e t i c a l t r e a t m e n t s of p r i m a r y c r e e p b e h a v i o r of c o m p o s i t e m a t e rials. de Silva 6 c o n s i d e r e d that the i n c r e a s e in c r e e p s t r a i n is due to a f a l l i n g s h e a r s t r e s s in a d i s c o n t i n u o u s l y r e i n f o r c e d c o m p o s i t e . He also a n a l y z e d that the l o a d - t r a n s f e r f r o m the m a t r i x to f i b e r s is due to a s t r e s s r e l a x a t i o n i n the m a t r i x of a c o n t i n u o u s l y r e i n f o r c e d composite. Although his a p p r o a c h s e e m e d to be useful in studying the p r i m a r y creep, ~2 his r e s u l t s did not lead to a closed f o r m equation for the t i m e - d e p e n d e n t i n c r e a s e in c r e e p s t r a i n . The p r e s e n t work d e s c r i b e s a c r e e p model of c o m p o s i t e m a t e r i a l s in t e r m s of c r e e p p a r a m e t e r s of the m a t r i x and f i b e r s . The following t h r e e a s s u m p t i o n s a r e made for the f o r m u l a t i o n of the model: 1) loadt r a n s f
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