Experiments on fracture behavior of single fiber-brittle zone model composites
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artificial composites, chemical reaction between the f i b e r and the m a t r i x often t a k e s p l a c e . T h e f o r m e d r e a c t i o n p h a s e at the i n t e r f a c e ( h e r e a f t e r n a m e d as zone in t h i s p a p e r ) is , in g e n e r a l , b r i t t l e and t h e r e f o r e it f r a c t u r e s at a s m a l l s t r a i n , r e s u l t i n g in a f o r m a t i o n of a c i r c u m f e r e n t i a l notch a r o u n d the f i b e r . If the i n t e r f a c i a l bonding b e t w e e n the f i b e r and the b r i t t l e zone is s t r o n g , the f o r m e d n o t c h e x t e n d s into the f i b e r , r e s u l t i n g in a l o s s of c o m p o s i t e s t r e n g t h . 1-a On the o t h e r hand, if the i n t e r r a c i a l bonding is weak and the e x e r t e d s h e a r s t r e s s at the i n t e r f a c e e x c e e d s the i n t e r r a c i a l s t r e n g t h , debonding b e t w e e n the f i b e r and the b r i t t l e zone a r i s e s . In this c a s e the s t r e n g t h of the f i b e r is not r e d u c e d b e c a u s e debonding c a u s e s blunting at the n o t c h - t i p . R e c e n t l y O c h i a i and M u r a k a m i ~ p r o p o s e d a t h e o r y to p r e d i c t the s t r e n g t h of f i b e r s as a function of t h i c k n e s s of the b r i t t l e zone f o r v a r i o u s i n t e r r a c i a l b o n d ing s t r e n g t h s . In t h e i r t h e o r y , the s t r e n g t h of the f i b e r with s t r o n g l y a d h e r i n g b r i t t l e zone was p r e d i c t e d on the b a s i s of f r a c t u r e m e c h a n i c s and the c o n d i t i o n s f o r debonding to a r i s e was obtained with the aid of the s h e a r lag a n a l y s i s p r o p o s e d by Cox. 6 A c c o r d i n g to O c h i a i and M u r a k a m i ' s t h e o r y , the s t r e n g t h of the f i b e r is s t r o n g l y dependent upon the i n t e r f a c i a l bonding, and, f o r the c a s e of s t r o n g i n t e r r a c i a l b o n d ing, t h e r e is a p e r m i s s i b l e t h i c k n e s s of the b r i t t l e zone, CI, below which no d e g r a d a t i o n e f f e c t of the b r i t t l e zone on the f i b e r s t r e n g t h e x i s t s . F o r the p r e d i c t i o n of the v a l u e of CI, we n e e d the v a l u e s of f r a c t u r e t o u g h n e s s K c or s t r a i n e n e r g y r e lease rate (crack a r r e s t fracture toughness value) G*c of the f i b e r . H o w e v e r , today, t h e r e a r e few t e c h niques to m e a s u r e t h e s e v a l u e s b e c a u s e the d i a m e t e r of the f i b e r i s too s m a l l . The a i m s of the p r e s e n t p a p e r a r e to i n v e s t i g a t e e x p e r i m e n t a l l y the s t r e n g t h of the f i b e r - b r i t t l e zone c o m p o s i t e with s t r o n g and weak i n t e r r a c i a l bondings, t o p r e s e n t a e x p e r i m e n t a l p r o c e d u r e to m e a s u r e the SHOJ1RO OCHIAI is Associate Researcher, SHUICHI URAKAWA is Graduate Student, KEI AMEYAMAis Student, and YOTARO MURAKAMI is Professor, Department of Metallu
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