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The materials used were commercially available tough pitch copper and two kinds of alpha brass. The sheet material was approximately 3 mm thick. Chemical a n a l y s e s of t h e s e m a t e r i a l s a r e given in T a b l e I. The two types of t e s t p i e c e s a r e shown in Fig. 1. A f t e r HITOSHI ISHII is Associate Professor, Department of Mechanical Engineering,Shizuoka University, Johoku, Hamamatsu 432, Japan. KAZUHIKOYUKAWAis Engineer, Matsushita Electric Works, Hikone 522, Japan. Manuscript submitted August 15, 197 8. METALLURGICALTRANSACTIONSA

m a c h i n i n g , the s a m p l e s were a n n e a l e d u n d e r v a r i o u s conditions to obtain d i f f e r e n t g r a i n s i z e s . T h e n they w e r e d e f o r m e d in t e n s i o n . The a m o u n t s of these p l a s tic p r e s t r a i n s r a n g e d f r o m 0 (as annealed) to a m a x i m u m of 28 pet. Type a t e s t p i e c e s were made to obt a i n S-N c u r v e data as well as s t r e s s - s t r a i n c u r v e s ; type b t e s t p i e c e s were used for F C P m e a s u r e m e n t s . Type b t e s t p i e c e s contained a c e n t r a l slit, the d e t a i l s of which a r e shown in F i g . 1, that was m a c h i n e d in after p r e s t r a i n i n g . A l l t e s t p i e c e s were polished m e c h a n i c a l l y p r i o r to t e s t i n g at r o o m t e m p e r a t u r e in n o r m a l l a b o r a t o r y a i r . The cyclic s t r e s s was a x i a l and its f r e q u e n c y was 60 Hz for all t e s t s . Cyclic s t r e s s s t r a i n c u r v e s were obtained by plotting the s t a b i l i z e d cyclic s t r a i n r e s p o n s e as a function of a c o n t r o l l e d s t r e s s , i n s t e a d of the u s u a l method of plotting the s t a b i l i z e d cyclic s t r e s s r e s p o n s e as a function of a c o n t r o l l e d s t r a i n . C r a c k lengths were m e a s u r e d with a 40X m i c r o m e t e r t e l e s c o p e using s t r o b o s c o p i c i l l u m i n a t i o n as a function of the n u m b e r of c y c l e s , N without stopping the fatigue m a c h i n e . T h e s e data were r e duced to c r a c k p r o p a g a t i o n r a t e s , da/dN, as a function of the s t r e s s i n t e n s i t y f a c t o r , AK, for a c e n t e r notched sheet, s That is, the s t r e s s i n t e n s i t y f a c t o r is given by the e x p r e s s i o n :

where 2a is a c r a c k length, A~ = emax - ~ r mni is a r a n g e of c y c l i c s t r e s s and w is the s p e c i m e n width. E X P E R I M E N T A L RESULTS The monotonic t e n s i l e p r o p e r t i e s a r e shown in F i g . 2. The 0.2 pct offset yield s t r e n g t h , Cry, as well as the t e n s i l e s t r e n g t h , aU, i n c r e a s e d as p r e s t r a i n i n c r e a s e d . T h e s e s t r e n g t h s , at the s a m e p r e s t r a i n , i n c r e a s e d t h r o u g h the s e q u e n c e of copper, 90/10 b r a s s and 70/30 b r a s s . The stacking fault e n e r g y (SFE) d e c r e a s e s through the s a m e s e q u e n c e . However, the r