An innovative technique for measuring the high strain rate response of sandwich composites

Foam core sandwich composites have been tested under high strain rate (HSR) loading in the thickness direction. An innovative experimental configurati on has been designed for this purpose. Conventional split Hopkinson pressur e bar (SHPB) technique 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 insignificant especiall y when testing soft materials. New sets of mathematical formulations have b een derived to account for the impedance mismatch between the incidence and transmitter bars. The modified equations are first verified with a known m aterial and thm used for sandwich composites. Three types of cores with var ious densities have been tested under compression at strain rates ranging f rom quasi-static to 1000 S-1. The compressive failure stress has been obser ved to be directly proportional to the core density, as well as to the stra in rate. The strain rate sensitivity was moderate, and the sandwich composi tes mostly failed by the collapse of the foam-cell. Delamination did not pl ay a major role in the failure process. Details of the mathematical derivat ions and the analysis of the HSR behavior are presented in this paper. (C) 2000 Elsevier Science Ltd. All rights reserved.