Deformation characteristics of zinc foam
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a p r e v i o u s study 1 of the d e f o r m a t i o n r e s p o n s e of a l u m i n u m alloy foams, two c o l l a p s e m e c h a n i s m s were o b s e r v e d which involved p r i m a r i l y e i t h e r b u c k l i n g or f r a c t u r e of the cell walls. These m e c h a n i s m s w e r e o b s e r v e d in a l u m i n u m and 7075 alloy foams r e s p e c tively and w e r e m a r k e d by different c o m p r e s s i o n s t r e s s - s t r a i n r e s p o n s e s . F o r the a l u m i n u m foam, the s t r e s s - s t r a i n c u r v e s w e r e snaooth and c o n t i n u ous, w h e r e a s for the 7075 alloy, the c u r v e s showed l a r g e i r r e g u l a r i t i e s and s e r r a t i o n s . A second o b s e r vation m a d e in this work was that for a given d e n s i t y r a t i o , the flow s t r e s s of an A1-7 pct Mg foam was g r e a t e r than that of the 7075 foam, although the bulk A1-7 pct Mg alloy has a much lower flow s t r e s s than that of the 7075 alloy. These r e s u l t s for the flow s t r e s s of a l u m i n u m alloy foams did not a g r e e with the p r e d i c t e d v a l u e s given by m o d e l s which have been s u c c e s s f u l for p o l y m e r f o a m s . ~'-6 An e l a s t i c b u c k l i n g c r i t e r i o n is used in these m o d e l s which, when applied to the m e t a l foams, gives v a l u e s for the flow s t r e s s s e v e r a l o r d e r s of m a g n i t u d e too high and f u r t h e r m o r e does not p r e d i c t the low flow s t r e s s of the a l u m i n u m foam in c o m p a r ison to that of the two alloy f o a m s . The e l a s t i c m o d ulus is e s s e n t i a l l y unchanged for t h e s e t h r e e m a t e r i als and t h e r e f o r e f r o m these m o d e l s , the f o a m s would be expected to have e s s e n t i a l l y the s a m e flow s t r e s s . In c o n s i d e r i n g these r e s u l t s ~ it was a p p a r e n t that the p r o p e r t i e s of the foam a r e not s i m p l y r e l a t e d to the bulk m a t e r i a l p a r a m e t e r s alone, but a r e the r e s u l t a n t of an i n t e r d e p e n d e n t r e a c t i o n between them, the c o l l a p s e m e c h a n i s m and the g e o m e t r y or s t r u c t u r e of the foam. T h e r e f o r e to e x a m i n e f u r t h e r the r e l a t i o n s h i p between t h e s e v a r i o u s f a c t o r s , a study was made of the t e m p e r a t u r e d e p e n d e n c e of the flow s t r e s s and e n e r g y a b s o r b i n g c h a r a c t e r i s t i c s of zinc foam. Zinc, a hexagonal c l o s e packed m e t a l , at r o o m t e m p e r a t u r e d e f o r m s p r i m a r y by b a s a l slip, m e c h a n i c a l twinning and kinking. Although the i n c i d e n c e of l a r g e s c a l e n o n b a s a l slip, e . g . {1122} (1123> or {1010}
P. H. THORNTONand C. L, MAGEEare with Scientific Research Staff, Ford Motor Co., Dearborn, MI 48121. Manuscript submitted October 23, t 974. METALLURGICALTRANSACTIONSA
(21[0> slip is p r o b a b l y r a r e at r o o m t e m p e r a t u r e , the i n c
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