Strain-rate effects on elastic and early cell-collapse responses of a polystyrene foam

The compressive behavior of a polystyrene foam was investigated at strain rates from 0.001 to 950/s. A hydraulically driven test machine was used for the quasi-static tests, and a modified split Hopkinson pressure bar (SHPB) was utilized for the dynamic tests. The shape of the incident pulse in the SHPB was carefully controlled so that the resulting stress–strain curves are valid starting from a small value of strain in the elastic region until past the initiation of cell-crushing. The collapse stress of the foam is found to increase nearly linearly with the logarithm of the strain rate, and the elastic modulus is seen to increase with strain rate. A rate-dependent phenomenological material model is employed to describe the experimental results.