  Simulations of the dynamic deformations of metal samples require
elastic-plastic constitutive updates of the material behavior to be performed
over a small time step between updates, as dictated by the Courant condition.
Depending on the deformation conditions, the converged time step becomes short
(~$10^{-9} s$ or less). If an implicit constitutive update is applied to this
class of simulation, the benefit of the implicit update is negated, and the
integration is prohibitively slow. The present work recasts an implicit update
algorithm into an explicit form, for which each update step is five to six
times faster, and the compute time required for a plastic update approaches
that needed for a fully-elastic update. For dynamic loading conditions, the
explicit model is found to perform an entire simulation up to 50 times faster
than the implicit model. The performance of the explicit model is enhanced by
adding a subcycling algorithm to the explicit model, by which the maximum time
step between constitutive updates is increased an order of magnitude. These
model improvements do not significantly change the predictions of the model
from the implicit form, and provide overall computation times significantly
faster than the implicit form over finite-element meshes. These modifications
are also applied to polycrystals via Taylor averaging, where we also see
improved model performance.
