Split Hopkinson pressure bar experiments on polymeric foams

Proper modifications are required when a split Hopkinson pressure bar (SHPB) is used to determine the dynamic compressive proper-ties of polymeric foams. Pulse shaping is necessary to ensure valid testing conditions: constant strain-rate deformation under dynamically equilibrated stresses, which need to be experimentally verified. A more sensitive method must be employed to examine the weak signal transmitted through the foam specimen. These necessary dynamic experimental techniques for polymeric foam testing are briefly reviewed. As an example, the dynamic compressive stress-strain behaviour of a rigid polyurethane foam with a density of 0.24 x 10(3) kg/m(3) has been determined at various strain rates using such a modified SHPB. Due to the low density and non-linear behaviour of the specimen, valid experimental results were obtained separately for small and large strains, respectively, since valid testing conditions could not be maintained over the entire duration of a dynamic experiment to large strains at high rate.