Effects of strain rate and deformation heating in tensile testing
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F O R M A B I L I T Y and f o r m i n g loads a r e n o r m a l l y a s s e s s e d by t e n s i l e t e s t r e s u l t s , although the s t r e s s s t a t e and s t r a i n r a n g e in p r a c t i c a l s h e e t m e t a l f o r m ing p r o c e s s e s d i f f e r f r o m those of the t e s t . A l s o the e f f e c t s of s t r a i n r a t e and d e f o r m a t i o n h e a t i n g in r o o m t e m p e r a t u r e t e s t s have g e n e r a l l y b e e n n e g l e c t e d . R e c e n t l y the s t r a i n r a t e e f f e c t s in the t e n s i l e t e s t have b e e n i n v e s t i g a t e d using a n u m e r i c a l a n a l y s i s by Ghosh.: The effect of d e f o r m a t i o n h e a t i n g has b e e n a n a l y z e d in the t e n s i l e t e s t by T r o o s t and E1Schennawi, 2 and in the c o m p r e s s i o n t e s t t a k i n g h e a t conduction into account by L a h o t i and A l t a n . 3 The s i m u l t a n e o u s effect of s t r a i n r a t e and deformation h e a t i n g on the s t r a i n - h a r d e n i n g of a d e e p - d r a w i n g q u a l i t y s t e e l has b e e n e x p e r i m e n t a l l y i n v e s t i g a t e d by K l e e m o l a and R a n t a - E s k o l a , 4 who d e v e l o p e d the equation ~ = 643-~~176176 0 . 0 0 1 5 ( T - To) } f o r des c r i b i n g the flow s t r e s s of t h i s s t e e l n e a r r o o m t e m p e r a t u r e . D e f o r m a t i o n h e a t i n g and s t r a i n r a t e have an e v e n m o r e p r o n o u n c e d effect in t e n s i l e t e s t i n g of a u s t e n i t i c s t a i n l e s s s t e e l s a s shown by Korhonen, 5 who found that the u n i f o r m s t r a i n d e p e n d s on the cross-head speed. The a i m of the p r e s e n t w o r k was to a n a l y z e n u m e r i c a l l y the e f f e c t of s t r a i n , s t r a i n r a t e and d e f o r m a t i o n h e a t i n g on the s t r a i n - h a r d e n i n g of s h e e t s t e e l in the tensile test.
not be p h y s i c a l l y j u s t i f i e d in g e n e r a l , it m a y give u s e ful r e s u l t s in a l i m i t e d t e m p e r a t u r e r a n g e . K l e e m o l a and R a n t a - E s k o l a 4 found that f o r a f e r r i t i c A l - k i l l e d s h e e t s t e e l , Eq. [1] can be w r i t t e n in the form
w h e r e 0 is the t e m p e r a t u r e d i f f e r e n c e , T - To, and K, n, m and/3 a r e c o n s t a n t s . Diffuse N e c k i n g S t r a i n s The S w i f t - H i l l n e c k i n g condition 8 is given a s
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