Using richtmyer–meshkov instabilities to estimate metal strength at very high rates

Abstract

Recently, Richtmyer–Meshkov instabilities (RMI) have been proposed for studying strength at strain rates up to 107/ s. RMI experiments involve shocking a metal interface that has geometrical perturbations that invert and grow subsequent to the shock. As these perturbations grow, their growth may arrest, or they may grow unstably and eventually fail. The experiments observe the growth and arrest to study the specimen’s yield (deviatoric) strength. Along these lines we first review some RMI experimental results on Cu. Next, the paper presents explicit Lagrangian simulations used to help interpret the Cu RMI results and infer the strength, i.e. flow stress, of the target metal. A Preston-Tonks-Wallace (PTW) constitutive model is modified to be more accurate at the strain rates accessed in the experiment. The advantages and disadvantages of RMI, as compared to the Rayleigh–Taylor (shockless) instabilities that are used more commonly to infer strength, are discussed. The advantages of using simple velocimetry measurements in place of radiography are also discussed.