The Deformation of aluminum foams
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T H E p r e s e n c e of a few p e r c e n t of v o i d s in a s o l i d m a t e r i a l is a w e l l - k n o w n r e s u l t of s o l i d i f i c a t i o n and powder metallurgy processing techniques. Investigations of the ( a l m o s t always) d e l e t e r i o u s effects of t h e s e voids have p r o c e e d e d on t h e o r e t i c a l and e x p e r i m e n t a l b a s e s and much work has n a t u r a l l y b e e n f o c u s s e d on f i n d i n g m e a n s for e l i m i n a t i n g the p o r o s i t y . 1 This p a p e r is c o n c e r n e d with s o l i d s where a d i f f e r e n t e x t r e m e in p o r o s i t y is p u r p o s e f u l l y p r e s e n t . A l u m i n u m b a s e f o a m s have been known for s o m e time 2 and a r e b e s t c h a r a c t e r i z e d as solid a l u m i n u m alloys c o n t a i n i n g g r e a t e r than about 50 v o l u m e pct voids. The a i m of the v a r i o u s p r o c e s s i n g t e c h n i q u e s is to o b t a i n a u n i f o r m high p o r o s i t y in a solid s t r u c t u r e . By a n a l o g y with the r e l a t e d c e l l u l a r f o r m s of r i g i d p o l y m e r i c m a t e r i a l s , 3 the m a j o r p o t e n t i a l a p p l i c a tions a r e in the s t i f f e n i n g of low weight s t r u c t u r e s , e . g . sandwich p a n e l s , and in e n e r g y a b s o r b i n g or c u s h i o n i n g applications. The" p u r p o s e of the p r e s e n t work was to i n v e s t i g a t e the influence of s e v e r a l m e t a l l u r g i c a l p a r a m e t e r s on the 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 A1 b a s e f o a m s . The p a r a m e t e r s include a l l o y c o m p o s i t i o n , heat t r e a t m e n t and f o a m d e n s i t y . Many of the p o l y m e r i c foam s y s t e m s have b e e n well c h a r a c t e r i z e d a'S but t h e r e a r e no p r e v i o u s s y s t e m a t i c s t u d i e s of m e t a l l i c f o a m s . T h e o r e t i c a l m o d e l s which have been e m p l o y e d for i n t e r p r e t ing the load d e f o r m a t i o n r e s p o n s e of f o a m s g e n e r a l l y a r e l i m i t e d to a b u c k l i n g a n a l y s i s of a s p e c i f i c g e o m e t r i c a l s t r u c t u r e 6 - u and do not c o n s i d e r o t h e r d e f o r m a tion p h e n o m e n a or the r e a s o n s for the v a r i o u s s h a p e s of the s t r e s s - s t r a i n c u r v e s for d i f f e r e n t foam m a t e r i a l s . S e v e r a l a d v a n t a g e s in s t u d y i n g a l u m i n u m r a t h e r than p o l y m e r i c f o a m s should also be noted. F o r e x a m ple, c h a n g e s i n the bulk m a t e r i a l p r o p e r t i e s c a n be m a d e by heat t r e a t m e n t without c o n c o m m i t a n t c h a n g e s in the e l a s t i c m o d u l u s o In addition, the c o l l a p s e mode c a n be d e t e r m i n e d d i r e c t l y by a m e t a l l o g r a p h i c t e c h n i q u e . F o r the p u r p o s e s of the work r e p o r t e d h e r e , it is i m p o r t a n t to r e c o g n i z e that s e v
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