  A detailed theoretical and numerical investigation of the infinitesimal
single-crystal gradient plasticity and grain-boundary theory of Gurtin (2008)
"A theory of grain boundaries that accounts automatically for grain
misorientation and grain-boundary orientation". Journal of the Mechanics and
Physics of Solids 56 (2), 640-662, is performed. The governing equations and
flow laws are recast in variational form. The associated incremental problem is
formulated in minimization form and provides the basis for the subsequent
finite element formulation. Various choices of the kinematic measure used to
characterize the ability of the grain boundary to impede the flow of
dislocations are compared. An alternative measure is also suggested. A series
of three-dimensional numerical examples serve to elucidate the theory.
