Computational Modeling of Stress-Wave-Induced Martensitic Phase Transformations in NiTi

Abstract

Computational simulations based on time-dependent Ginzburg—Landau equations are used to model martensitic phase transformations induced in pressure-shear plate impact experiments. Symmetric impact experiments on polycrystalline NiTi plates, and so-called “sandwich impact” experiments on thin polycrystalline NiTi foils sandwiched between two hard plates, are simulated by characterizing each grain as a three-dimensional finite element that can transform to twinned martensite involving twenty-four habit plane variants. The threshold stress at which the transformation occurs is obtained from the amplitude of the leading shear wave in the symmetric impact experiments. The kinetic coefficient in the Ginzburg—Landau equation is obtained by matching the risetime of the transverse particle velocity in the sandwich impact experiments. These simulations highlight the importance of including the effects of self-accommodation in which clusters of several habit plane variants nucleate and grow simultaneously to reduce the constraining effect of the surrounding material.