Comparison of load relaxation data of type 316 austenitic stainless steel with Hart's deformation model
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paper r e p o r t s the p l a s t i c d e f o r m a t i o n p r o p e r t i e s of Type 316 s t a i n l e s s s t e e l f r o m the viewpoint of a p l a s t i c equation of state. The concept of a p l a s t i c equation of state adopted in the p r e s e n t work was f i r s t i n t r o d u c e d by Hart.1 R e c e n t e x p e r i m e n t a l and t h e o r e t i c a l p r o g r e s s on this s u b j e c t has been s u m m a r i z e d in Ref. 2. Hart s u g g e s t s that a p l a s t i c equation of state can be f o r m u l a t e d in t e r m s of s t r e s s , p l a s t i c s t r a i n r a t e , t e m p e r a t u r e and a h a r d n e s s p a r a m e t e r . The e x i s t e n c e of this type of p l a s t i c equation of state can be tested by p e r f o r m i n g load r e laxation e x p e r i m e n t s . At a given t e m p e r a t u r e the load r e l a x a t i o n e x p e r i m e n t s g e n e r a t e s t r e s s - p l a s t i c s t r a i n r a t e r e l a t i o n s h i p s at e s s e n t i a l l y constant h a r d n e s s . It has been d e m o n s t r a t e d in a v a r i e t y of m e t a l s and c o m m e r c i a l a l l o y s that the s t r e s s - p l a s tic s t r a i n r a t e r e l a t i o n s h i p s at different h a r d n e s s e s can be obtained by d e f o r m i n g the m a t e r i a l to v a r i o u s p l a s t i c s t r a i n levels p r i o r to load r e l a x a t i o n and a r e r e l a t e d by s c a l i n g ? This type of b e h a v i o r j u s t i f i e s the concept i n t r o d u c e d by Hart and s u g g e s t s that the c o n s t a n t h a r d n e s s s t r e s s - p l a s t i c s t r a i n r a t e r e l a t i o n s h i p uniquely s p e c i f i e s the h a r d n e s s state of the m a t e r i a l . Recently the p h e n o m e n o l o g i c a l t h e o r y of a p l a s t i c equation of state has b e e n extended by Hart, 3 who proposed a d e f o r m a t i o n m o d e l c o n s i s t i n g of e s s e n t i ally two p a r a l l e l b r a n c h e s . One of the b r a n c h e s , r e p r e s e n t i n g d i s l o c a t i o n glide c o n t r o l l e d p r o c e s s e s , is i m p o r t a n t at lower homologous t e m p e r a t u r e s . The other b r a n c h c o n t a i n s no c o n t r i b u t i o n f r o m d i s l o c a tion glide c o n t r o l l e d p r o c e s s e s and p r e d o m i n a t e s at higher homologous t e m p e r a t u r e s . Load relaxation experiments on Type 316 austenitic stainless steel at room temperature have demonstrated that this material follows Hart's plastic equation of state. 4 In this paper the results of load relaxation experiments performed at temperatures up to 500~ are reported. These results exhibit the entire range of behavior suggested by the phenomenologicalmodel of Harta and will be analyzed in terms of this model.
F. H. HUANG is Research Associate, Department of Materials Science and Engineering,Cornell University. Ithaca, NY 1485.3. F. V. ELLIS, formerly Post-Doctoral Associate, Department of Materials Science and Engineering,Cornell University. is now wi
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