Shock‐Wave Studies of PMMA, Fused Silica, and Sapphire

The shock‐wave propagation characteristics of polymethyl methacrylate (PMMA), fused silica, and sapphire were measured for both compressive and rarefaction waves using plate‐impact experiments and interferometer instrumentation techniques. The peak stress levels in the experiments were 22, 65, and 120 kbar, respectively. The high‐resolution measurements of the stress wave profiles showed the PMMA to be a complex material whose wave propagation is influenced by nonlinearity, strain‐rate dependence, and elastic‐plastic effects in which plastic working increases the zero‐pressure volume of the material. The fused silica is very well characterized as a nonlinear elastic material having the interesting property of propagating stable rarefaction shock waves. The sapphire was nearly linear elastic to 120 kbar. The use of these three transparent materials as ``windows'' in laser interferometer instrumented shock‐wave studies of other materials is discussed. The effect of the shock‐induced variation of the index o...