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

Abstract

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 of refraction on the interferometer data was also measured and is presented.