The effect of high strain rate compression on closed-cell aluminum foams

摘要

The compressive deformation behavior of closed-cell aluminum foams was assessed in air under static and dynamic loading conditions. High strain rate experiments were conducted in our laboratory using a split Hopkinson pressure bar system at strain rates ranging from 400 s~(-1) to 2500 s~(-1). A servo-controlled hydraulic test machine was used for compression tests at strain rates ranging from 10~(-5) s~(-1) to 1 s~(-1). A strain rate effect was demonstrated for Alporas, a closed-cell aluminum foam, and was most significant for a higher density foam (i.e., 15% relative density). The effect is attributed to the presence and influence of gas within the closed cell structure. This was confirmed by testing samples with very small holes drilled through the cell walls to permit uninhibited intercellular gas flow. The buildup of gas pressure within the cell walls eventually causes some of them to rupture. Initial damage appears to be concentrated at the sample surface, progressing with time through the sample and destabilizing sequentially the internal cell walls. This results in the formation of isolated deformation bands. The experimental results are discussed in reference to recent findings by other investigators on the dynamic behavior of similar closed-cell aluminum foams.