Strength of tantalum shocked at ultrahigh pressures

Abstract

High purity polycrystalline tantalum (Ta) was shocked through 1 to 3.5 Mbar pressures creating Richtmyer-Meshkov unstable interfaces that were used to determine the dynamic material strength. The experiments were performed on the Omega laser at the University of Rochester Laboratory for Laser Energetics. Prior to shock, the driven surfaces of the tantalum targets where coined with a sinusoidal pattern. The targets were recovered post-shock, and the growth of the sinusoid amplitudes was used to characterize the relative extent of plastic deformation as a function of laser energy. Analogous data were extracted prior to the experiments from phenomenological Von Mises plasticity simulations that considered equation of state tables for Ta. The simulations showed the best agreement with the experiments (less than 5% difference between mean ripple growth measures) for shock pressures ranging from 1.2 to 2.7 Mbar. A fluid model studied as a function of viscosity was also used to qualitatively indicate the sensitivity of the experiments to strength. These results verify the ability to use a phenomenological, equation of state based model to simulate very high-strain rate, high-pressure deformation of tantalum.

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