Effect of plastic strain on the r value of textured steel sheet
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o
E.
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I100
I
i
tOO0
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i
i
2000 [K
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2500 i .(n'iPa
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Fig. 3 - - M e a s u r e m e n t s of the monotonic plastic zone s i z e s of CT s p e c i m e n s . The r e s u l t s for plane s t r e s s (upper curve) and plane s t r a i n (lower curve) conditions a r e given. The A coefficients w e r e calculated with Cry - 1070 MPa,
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o O~oA=
4.13
lo--' E r~
rr
o
5 164 o
o
2000
o
o
4000
I
6000
8000
(K
max)
I
10 0(~0 2, ( M P a . m ~ )
2
Fig. 4 - - V a r i a t i o n of the monotonic p l a s t i c zone s i z e s of SEN s p e c i m e n s with Kmax. The r e s u l t s for plane s t r e s s (upper curve) and plane s t r a i n (lower curve) conditions a r e included. The A coefficients w e r e calculated with cry = 1070 MPa. F i g . 2 s h o w s a n e x a m p l e of t h e d e c o r a t i o n b y p l a t e l e t s of t h e p l a s t i c z o n e a t t e n d i n g a f a t i g u e c r a c k . It c a n b e n o t e d t h a t t h e p r e s e n c e of t h e ~ p h a s e w i t h i n t h e g r a i n s i s r e s t r i c t e d to a z o n e b e l o w t h e f r a c t u r e s u r f a c e . In t h e r e g i o n s w h i c h w e r e n o t d e f o r m e d , t h e p r e c i p i t a t i o n of t h e o r t h o r h o m b i c p h a s e o c c u r s o n l y at the grain boundaries. Inside the plastic zone, the d e n s i t y of ~ p l a t e l e t s i n c r e a s e s c o n t i n u o u s l y f r o m t h e elastoplastic boundary or the monotonic zone interface to t h e f r a c t u r e s u r f a c e , It i s n o t p o s s i b l e t o d e t e r m i n e t h e l i m i t of t h e r e v e r s e d z o n e b y t h i s e t c h i n g t e c h n i q u e . M o r e o v e r t h e a c c u r a c y of t h i s e t c h i n g t e c h n i q u e to d e l i n e a t e t h e p l a s t i c z o n e s i s t h o u g h t to b e of t h e o r d e r of t h e g r a i n s i z e , i . e . • 9 10 -8 m . T h e m o n o t o n i c p l a s t i c z o n e s i z e (Rp) w a s m e a s u r e d on various specimens and for various crack lengths in o r d e r t o s t u d y a l a r g e r a n g e of AK. T h e r e s u l t s f o r C T a n d SEN s p e c i m e n s a r e g i v e n i n F i g s . 3 a n d 4, r e s p e c t i v e l y . In b o t h c a s e s r e s u l t s f o r p l a n e s t r a i n a n d p l a n e stress measurements are included. The surface meas u r e m e n t s w e r e f o u n d to b e in g o o d a g r e e m e n t w i t h those observed from deformation zone, The plastic z o n e s i z e s a r e p l o t t e d v s (Kmax) 2, w h e r e K m a x i s t h e m a x i m u m of t h e s t r e s s - i n t e n s i t y factor. The monoMETALLURGICAL TRANSACTIONS A
tonic plastic zone is thought to be best correlated with Kma x r a t h e r t h a n AK. T h e r e s u l t s s h o w t h a t t h e I r w i n ' s r e l a t i o n s h i p , Rp = A • ( K / a y ) a f o r m o n o t o n i c p l a s t i c flow i s v e r i f i e d . The plane strain plastic zone is approximately half the plane stress plastic zone. This ratio is larger than that p r e d i c t e d b
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