Temperature and strain rate dependence of cyclic deformation response and damage accumulation in ofhc copper and 304 sta
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u r e p r o c e s s e s . Also, included in t h i s s t u d y i s the i n fluence of t e m p e r a t u r e and s t r a i n r a t e on d a m a g e a c c u m u l a t i o n , and in p a r t i c u l a r the influence of d a m a g e a c c u m u l a t e d b y one m e c h a n i s m (e.g., c r e e p ) on the d a m a g e a c c u m u l a t i o n p r o c e s s o p e r a t i n g under c o n d i t i o n s w h e r e a n o t h e r m e c h a n i s m (e.g., fatigue) is d o m inant. M A T E R I A L S AND E X P E R I M E N T A L PROCEDURE The m a t e r i a l s u s e d in t h i s w o r k w e r e OFHC c o p p e r and AISI 304 s t a i n l e s s s t e e l . The c o p p e r s p e c i m e n s w e r e a n n e a l e d at 650~ for 189 h in v a c u u m and f u r n a c e cooled. The 304 s t a i n l e s s s t e e l was s o l u t i o n h e a t t r e a t e d at 1020~ f o r 1 h followed by w a t e r quenching. S t r a i n c y c l i n g of the s p e c i m e n s (0.3 in. gage length, 0.25 in. diam) was c a r r i e d out u s i n g a c l o s e d loop s e r v o c o n t r o l l e d e l e c t r o h y d r a u l i c t e s t i n g s y s t e m . Most of the w o r k was c a r r i e d out u s i n g a fully r e v e r s e d s t r a i n r a n g e of 0.020. The s t r a i n - t i m e w a v e - f o r m was a fully r e v e r s e d t r i a n g l e . All high t e m p e r a t u r e t e s t s w e r e conducted u n d e r an a r g o n a t m o s p h e r e . The i n d e p e n d e n t t e s t i n g v a r i a b l e s w e r e t e m p e r a t u r e ( - 75 to 760~ and s t r a i n r a t e (2 x 10 -4 to 4 x 10 "1 p e r s). This l a t t e r was a c c o m p l i s h e d by f r e q u e n c y c h a n g e s (0.005 to 10 c p s r e s p . ) . In t e s t s w h e r e the t e m p e r a t u r e was changed, f r e e e x p a n s i o n of the s p e c i m e n under z e r o l o a d c o n d i t i o n s w a s a l l o w e d d u r i n g the change of t e m p e r a t u r e . A c o m p l e t e d e s c r i p t i o n of the s p e c i m e n d e s i g n and the e x p e r i m e n t a l p r o c e d u r e can be found in Ref. 1. E x a m i n a t i o n of the d i s l o c a t i o n s u b s t r u c t u r e was c a r r i e d out u s i n g a P h i l i p s EM200 t r a n s m i s s i o n e l e c t r o n m i c r o s c o p e , w h e r e a s s u r f a c e d a m a g e and f r a c t o g r a p h y VOLUME 5, JANUARY 1974-267
5oi~
OFHC COPPER o
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A~T=O.O0
6
:
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{< 30
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N 20
-75~
o
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25~ 500~
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i
I
102
IO I
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i0 4
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CYCLES
Fig. 1--Stress response with cycles for copper at different temperatures. 8~Ir
AISI
304 STAINLESS STEEL
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=
~-
70
e
: 2xlO
j
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25 ~c
Fig. 3--Dislocation substructure in copper cycled at ACT = 0.020 at 25~ Magnification 30,100 times.
~s 40
760 o C
20
I I00
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1
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104
CYCLES
Fig. 2--Stress response with cycles for type 304 stainless steel at different temperatures. were studied u s i n g a C a m
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