  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.
