Material properties, including strain-rate effects, as related to sheet metal forming
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sheet m e t a l p r e s s f o r m i n g , the t h r e e p r i n c i p l e p a r a m e t e r s to f o r m a given p a r t a r e p r e s s - s e t t i n g , l u b r i c a t i o n , and m a t e r i a l p r o p e r t i e s . E x p e r i e n c e has shown that p r e s s setting, including die b a r b e r i n g , and l u b r i c a t i o n and m a t e r i a l p r o p e r t i e s . E x p e r i e n c e has p e r i e n c e d die s e t - u p man can by s e l e c t i v e t r i a l and e r r o r f o r m a v a r i e t y of p a r t s with the s a m e m a t e r i a l ; h o w e v e r , p r e s s a d j u s t m e n t s and die m o d i f i c a t i o n s for such a p r o c e d u r e may take days to w e e k s and may r e q u i r e continual manipulation. L i k e w i s e a p a r t f o r m i n g w e l l with a given lot of m a t e r i a l may suddenly s t a r t t e a r i n g by s i m p l y changing the l u b r i c a n t o r e v e n l u b r i cation t e c h n i q u e . Even though p r e s s setting and l u b r i cation a r e m o s t c r i t i c a l to f o r m i n g , the m a j o r s a v i n g s for high v o l u m e i t e m s a r e to be a c h i e v e d by m a t e r i a l p r o p e r t i e s o p t i m i z a t i o n , allowing the u s e of a l e s s e x p e n s i v e m a t e r i a l . The w o r k h e r e is a i m e d at b e t t e r u t i l i z a t i o n of m a t e r i a l through m a t e r i a l p r o p e r t i e s opt i m i z a t i o n , s t r a i n - r a t e effects included. The p a p e r has two p a r t s . Uniaxial s t r e s s t e n s i l e p r o p e r t i e s a r e d i s c u s s e d and v a l u e s p r e s e n t e d f o r two l o w - c a r b o n sheet s t e e l s up to s t r a i n r a t e s of 102 p e r s e c . In the second part, two flat sheet p r o b l e m s a r e a n a l y z e d , one s i m u l a t i n g pure s t r e t c h i n g and one s i m ulating a c o m p l e x type of s t r e t c h i n g . C a l c u l a t i o n s a r e p e r f o r m e d with m a t e r i a l p r o p e r t i e s typical of d i f f e r ent g r a d e s of sheet s t e e l to show the effect of a n i s o t r o p y , s t r a i n hardening and s t r a i n r a t e on s t r a i n d i s tribution.
t e s t s r e q u i r e d for studying p r e s s f o r m i n g , h o w e v e r , it is n e c e s s a r y that the r a n g e of s t r a i n r a t e s be d e t e r m i n e d . Ref. l p r e s e n t s a s i m p l e c a l c u l a t i o n in which f o r m i n g s t r a i n r a t e s a r e found to be in the r a n g e of 1.5 p e r s e c , a value t h r e e o r d e r s of m a g n i t u d e above s t a n d a r d t e s t r a t e s . In the f o r m i n g of c o m p l e x p a r t s , highly l o c a l i z e d , o c c u r r i n g quickly s t r a i n s tend to during the d e f o r m a t i o n p r o c e s s o v e r s h a r p e d g e s o r in s m a l l f i l l e t s and t h i s r e s u l t s in h i g h e r s t r a i n r a t e s f o r the s a m e p r e s s s p e e d s . Knowledge of m a t e r i a l p r o p e r t i e s to m o d e r a t e s t r a i n r a t e s , 1 to 100 p e r s e c , is t
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