The rheological properties of annealed tantalum
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Previous mvestlgatmns h a v e s h o w n that t a n t a l u m , like o t h e r m e t a l s w i t h a bee c r y s t a l s t r u c t u r e , is r a t e s e n s i t i v e in i t s m e c h a n i c a l r e s p o n s e t o d e f o r m a t i o n . T h e d e t a i l s of t h i s r e s p o n s e a r e a l s o i n f l u e n c e d by o t h e r f a c t o r s , c h i e f a m o n g t h e m b e i n g the d e g r e e of purity and the thermomeehanical history. To control the p u r i t y a n d t h e m o m e c h a n i c a l h i s t o r y of o u r t e s t s p e c i m e n s , we c h o s e s p e c i m e n s m a c h i n e d f r o m a s i n g l e r o d of 99.9 p e t p u r e , f u l l y r e c r y s t a l l i z e d t a n t a lum o b t a i n e d f r o m K a w e c k i - B e r y l c o Industries. F o r t e s t s on t h e M T S a n d D y n a p a k m a c h i n e s , r o u n d t e n s i l e s p e c i m e n s w i t h a gage s e c t i o n 1.25 in. l o n g a n d 0 . 2 5 2 in. i n D i a m w e r e u s e d . F o r H o p k i n s o n b a r t e s t s , s p e c i m e n s w i t h a gage l e n g t h of 1 / 4 t o 1 / 2 in. a n d a d i a m of 0.16 i n . w e r e u s e d . T e n s i o n t e s t s a t s t r a i n r a t e s b e l o w 10 p e r s e e w e r e p e r f o r m e d on a n M T S M o d e l 311.11 h y d r a u l i c a l l y a c tuated u n i v e r s a l testing machine p r o g r a m m e d for a c o n s t a n t d i s p l a c e m e n t r a t e . F o r t e s t s s l o w e r than 0.01 s e e -~, s t r a i n w a s m e a s u r e d by a n I n s t r o n M o d e l G - 5 1 11 e x t e n s o m e t e r ; l o a d a n d s t r a i n w e r e p l o t t e d a s f u n c t i o n s of t i m e on a t w o - p e n s t r i p c h a r t r e c o r d e r . F o r K. G. HOGE is Mechanical Engineer, University of California Lawrence Radiation Laboratory, Livermore, Calif. P . P. GILLIS is Professor Engineering Mechanics, University of Kentuchky, Lexington, Ky. Manuscript submitted June 11, 1970. METALi. LJRGICAL TRANSACTIONS
t e s t s f a s t e r than 10-a s e e -z, a n O p t r o n M o d e l 680 o p t i c a l e x t e n s o m e t e r was used to m e a s u r e s t r a i n ; l o a d a n d s t r a i n w e r e p l o t t e d v s t i m e by a T e k t r o n i x M o d e l 555 d u a l - b e a m o s c i l l o s c o p e . In a d d i t i o n , l o a d v s s t r a i n w a s r e c o r d e d o n a T e k t r o n i x M o d e l 536 o s c i l l o s c o p e . F r o m s t r a i n r a t e s of 10 t o 150 s e e -1, t e s t s w e r e p e r f o r m e d on a D y n a p a k m e t a l w o r k i n g m a c h i n e m o d i f i e d f o r t e n s i o n l o a c i n g , s S p e c i m e n f o r c e was m e a s u r e d w i t h a s t r a i n - g a g e d l o a d c e l l i n s e r i e s w i t h the s p e c i m e n . Strain was m e a s u r e d u s i n g t h e O p t r o n M o d e l 680 e x t e n s o m e t e r , a n d d a t a w e r e r e c o r d e d on o s c i l l o s c o p e s as d e s c r i b e d above. F o r s t r a i n r a t e s a b o v e 500 s e e -~, t e s t s w e r e p e r f o r m e d by the s p l i t H o p k i n s o n
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