Effect of irreversible phase change on shock-wave propagation

New release adiabat data for vitreous GeO2 are reported up to similar to 25 GPa using the VISAR technique. Numerical modeling of isentropic release wa ve induced dynamic states achieved from one dimensional strain-stress waves is consistent with a phase change that induce an increase in zero-pressure density from 3.7-6.3 Mg/m(3) starting at similar to 8 GPa. The first relea se adiabat data for SiO2 (fused quartz) are presented (obtained with immers ed foil technique). Above 10 GPa, the SiO2 release isentropes, in analogy w ith GeO2, are steeper than the Hugoniot in the volume-pressure space, indic ating the presence of an irreversible phase transition (to a stishovite-lik e phase). We simulate propagation of shock-waves in GeO2, in spherical and planar symmetries, and predict enhanced attenuation for shock pressures (p) above the phase change initiation pressure (8 GPa). The pressure from a sp herical source decays with propagation radius r, p similar to r(x), where x is the decay coefficient. Modeling hysteresis of the phase change gives x = -2.71, whereas without the phase change, x = -1.15, An analytical model i s also given. (C) 1999 Elsevier Science Ltd. All rights reserved.