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F i g . 1 - - A n e x a m p l e o f e x c e p t i o n a l s u p e r p l a s t i c i t y in t h e P b - 6 2 p e t Sn e u t e c t i c a l l o y . S p e c i m e n A i s u n d e f o r m e d . S p e c i m e n B , h a v i n g a g r a i n s i z e of 6.9/~rn, w a s p u l l e d in t e n s i o n a t 413 K w i t h a n i n i t i a l s t r a i n r a t e o f 1.33 • 10 -4 s-l; the t e s t w a s d i s c o n t i n u e d p r i o r to f a i l u r e a t a n e l o n g a t i o n o f 4850 p c t .

In s u m m a r y : 1) F o u r s p e c i m e n s of the Pb-62 pct Sn eutectic a l loy, having a g r a i n s i z e of 6.9 pro, exhibited e x c e p tional ductility when pulled in tension at 413 K with an initial s t r a i n r a t e of 1.33 • 10 "4 s -1. The elongations at f a i l u r e w e r e ->3400 pct; for one specimen, the t e s t was discontinued p r i o r to f a i l u r e at an elongation of 4850 pct, r e p r e s e n t i n g the highest s t r a i n so f a r r e p o r t e d in a s u p e r p l a s t i c m a t e r i a l . 2) The p e r c e n t a g e elongations at f a i l u r e a r e about an o r d e r of magnitude higher than the value p r e d i c t e d by the theory of p l a s t i c i n s t a b i l i t i e s in tension c r e e p developed by Burke and Nix, ~ but they a r e in r e a s o n able a g r e e m mt with the e m p i r i c a l r e l a t i o n s h i p d e r i v e d by Morrisoff ) for round b a r s p e c i m e n s of the P b - S n eutectic.

This work was supported by the National Science Foundation under Grant No. DMR76-16596.

Communication: A Note on the Determination of Accurate Flow Properties from Simple Compression Tests

s e v e r a l d i a m e t e r to height r a t i o s and e x t r a p o l a t i n g the data obtained to z e r o d i a m e t e r to height r a t i o . In this note a method is d e s c r i b e d which allows a c o n s i d e r a b l e reduction in the work involved in obtaining t r u e s t r e s s s t r a i n data f r o m s i m p l e c o m p r e s s i o n tests; only two compression tests are required. F r o m a s i m p l e uniform c o m p r e s s i o n test the s t r a i n is calculated from the i n i t i a l and progressive s a m p l e d i m e n s i o n s and the applied s t r e s s is obtained from the load divided by the c u r r e n t s p e c i m e n c r o s s s e c tional a r e a . It is then n e c e s s a r y to r e m o v e the f r i c tional work contribution so that the t r u e m a t e r i a l flow s t r e s s can be obtained from the applied s t r e s s . Avitz u r s developed an upper bound solution to the p r o b l e m of uniform c o m p r e s s i o n of a solid c y l i n d e r between fiat dies; h e r e the applied s t r e s s (io) is r e l a t e d to the m a t e r i a l flow s t r e s s (%) by

R. L. WOODWARD The s i m p l e c o m p r e s s i o n test is ideal f o r the d e t e r mination of s t r e s s - s t r a i n data at high s t r a i n s and high s t r a i n r a t e s as is r e q u i r e d for p r e d i c t i o n s of t