The influence of hydrostatic pressure on the tensile deformation and fracture of copper
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f r a c t u r e o c c u r r e d e n t i r e l y by a s h e a r p r o c e s s and f r a c t u r e s t r a i n tended to a c o n s t a n t v a l u e . In the p r e s e n t paper an i n v e s t i g a t i o n into the effects of s u p e r i m p o s e d h y d r o s t a t i c p r e s s u r e on the t e n s i l e d e f o r m a t i o n and f r a c t u r e of a c o m m e r c i a l copper is r e p o r t e d . P a r t i c u l a r e m p h a s i s is placed on the v a r i a tion of d e f o r m a t i o n and f r a c t u r e m e c h a n i s m s with p r e s s u r e and a c o m p a r i s o n is made b e t w e e n the b e h a v i o r of copper and that found p r e v i o u s l y for a - b r a s s f
MATERIAL The m a t e r i a l used was e l e c t r o l y t i c tough pitch copp e r o r i g i n a l l y in the f o r m of 9.5 m m d i a m rod. C h e m ical a n a l y s i s of the m a t e r i a l showed that it contained 99.965 wt pct Cu with the p r i n c i p l e i m p u r i t y b e i n g oxygen (0.022 wt pct). T e n s i l e t e s t s p e c i m e n s of 4 m m gage diam and 10 m m gage length with s c r e w e d ends were m a c h i n e d f r o m the rod. T h e s e t e s t s p e c i m e n s were a n n e a l e d for 1 h at 600~ The m e a n g r a i n d i a m of the a n n e a l e d m a t e r i a l was 0.02 m m and the u l t i m a t e t e n s i l e s t r e n g t h was 223 J= 5 MPa. The gage lengths of the a n n e a l e d s p e c i m e n s w e r e lightly polished to r e move the oxide f o r m i n g d u r i n g a n n e a l i n g . E x a m i n a t i o n of the m i c r o s t r u c t u r e of the a n n e a l e d copper showed that it c o n t a i n e d m a n y s m a l l i n c l u s i o n s which were identified by e l e c t r o n m i c r o p r o b e a n a l y s i s as Cu20. Longitudinal s e c t i o n s of the m a t e r i a l showed the i n c l u s i o n s to be e i t h e r in the f o r m of individual e l l i p s o i d a l p a r t i c l e s or groups of p a r t i c l e s a r r a n g e d p a r a l l e l to the rod axis. T r a n s v e r s e s e c t i o n i n g of the copp e r showed all p a r t i c l e s to be a p p r o x i m a t e l y c i r c u l a r in c r o s s - s e c t i o n . A n u m b e r of i n c l u s i o n s of both f o r m s were t r a n s v e r s e l y c r a c k e d as shown in Fig. 1. T h e s e could provide a s o u r c e of void nuclei.
METHODS The high p r e s s u r e a p p a r a t u s has b e e n d e s c r i b e d p r e v i o u s l y . 7 B r i e f l y , it c o n s i s t s of a p r e s s u r i z e d c h a m b e r c o n t a i n i n g a t e n s i l e t e s t s p e c i m e n s c r e w e d into a c o n n e c t o r at the lower end and a rod, which p r o t r u d e s f r o m the c o n t a i n e r , at the upper end. The p r e s s u r e is allowed to f o r c e the r o d f r o m the c o n t a i n e r at a c o n t r o l l e d r a t e thus d e f o r m i n g the t e n s i l e s p e c i m e n . Using this method, s p e c i m e n s could be d e f o r m e d to f r a c t u r e or to any s t r a i n up to v e r y close to f r a c t u r e u n d e r h y
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