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.