Influence of undercooling upon relative nucleation kinetics of proeutectoid ferrite at austenite grain faces and grain e
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Influence of Undercooling Upon Relative Nucleation Kinetics of Proeutectoid Ferrite at Austenite Grain Faces and Grain Edges
500
% ~'400
W. F. LANGE
//unioxial
Ref
r
2
10
1.89
3
3
1.95
300 /
200
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I _ _
t
0.2
0.4
0.6
E:e
Fig. 3-Examples of uniaxial and biaxial stress-strain curves of A1 killed sheet steels having nearly equivalent r values (redrawn from experimental data referred to).
The r e s u l t s of Ghosh and Backofen 7 show a s t r o n g s t r a i n r a t i o dependence of the n value of sheet s t e e l . However, if the flow s t r e s s is d e t e r m i n e d f r o m p r e s t r a i n e d s a m p l e s by u n i a x i a l t e n s i l e t e s t s , the a c t u a l b i a x i a l flow s t r e s s cannot be obtained. In addition, it has b e e n shown that the effective u n i f o r m s t r a i n d e c r e a s e s d r a s t i c a l l y due to the p r e d e f o r m a t i o n in u n i a x i a l t e n s i l e t e s t s c a r r i e d out in two s t a g e s in diff e r e n t d i r e c t i o n s .15 It is t h e r e f o r e e v i d e n t that c o r r e c t effective s t r a i n v a l u e s cannot be c a l c u l a t e d by the H i l l ' s model, if the loading path is changed d u r i n g forming. C o n c l u s i o n s . The Hollomon equation was found to d e s c r i b e the u n i a x i a l and b i a x i a l s t r e s s - s t r a i n c u r v e s well, the u n i a x i a l and b i a x i a l n v a l u e s being n e a r l y e q u a l . H i l l ' s model of a n i s o t r o p y was used in the c o m p a r i s o n of the c u r v e s . The effective u n i a x i a l and b i a x i a l c u r v e s were c o i n c i d e n t , justifying the use of the u n i a x i a l m a t e r i a l p a r a m e t e r s , n and r, in the f o r m ability analysis. The author w i s h e s to thank D r . H. K l e e m o l a for most i n v a l u a b l e d i s c u s s i o n s d u r i n g the c o u r s e of this work.
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