Crystal Plasticity for Dynamic Loading at High Pressures and Strains

Abstract: A crystal plasticity theory was developed for use in simulations of dynamic loading at high pressures and strain rates. At pressures of the order of the bulk modulus, compressions o(100%) may be induced. At strain rates o(10^9)/s or higher, elastic strains may reach o(10%), which may change the orientation of the slip systems significantly with respect to the stress field. Elastic strain rather than stress was used in defining the local state, providing a more direct connection with electronic structure predictions and consistency with the treatment of compression in initial value problems in continuum dynamics. Plastic flow was treated through explicit slip systems, with flow on each system taken to occur by thermally-activated random jumps biased by the resolved stress. Compared with simple Arrhenius rates, the biased random jumps caused significant differences in plastic strain rate as a function of temperature and pressure, and provided a seamless transition to the ultimate theoretical strength of the material. The behavior of the theory was investigated for matter with approximate properties for Ta, demonstrating the importance of the high pressure, high strain rate contributions.