High Strain Rate Response of Resin Infusion Molded Sandwich Composites

Abstract

Foam core sandwich composites have been tested under high strain rate (HSR) loading in the thickness direction. The regular Split Hopkinson Pressure Bar (SHPB) has been modified by replacing the steel transmitter bar by a polycarbonate bar. This modification resulted in stronger signals from the transmitter bar, which would otherwise be very feeble especially when testing soft materials. New sets of mathematical formulations have been derived to account for the impedance mismatch between the incidence and transmitter bars. The modified equations are first verified with a known material and then used for sandwich composites. Three types of core with various densities have been tested under compression at strain rates ranging from quasi-static to 1000 S−1. The compressive failure stress has been observed to be directly proportional to the core density, as well as to the strain rate. The strain rate sensitivity was moderate, and the sandwich composites mostly failed by the collapse of the foam-cell. Delamination did not play a major role in the failure process. Details of the mathematical derivations and the analysis of the HSR behavior are presented in this paper.