  The effect of slip transfer on the deformation mechanisms of Al bicrystals
was explored using a rate-dependent dislocation-based crystal plasticity model.
Three different types of grain boundaries (GBs) were included in the model by
modifying the rate of dislocation accumulation near the GB in the Kocks-Mecking
law, leading to fully-opaque (dislocation blocking), fully-transparent and
partially-transparent GBs. In the latter, slip transmission is only allowed in
pairs of SS in neighbour grains that are suitably oriented for slip transfer
according to the Luster-Morris parameter. Modifications of the GB character led
to important changes in the deformation mechanisms at the GB. In general,
bicrystals with fully-opaque boundaries showed an increase in the dislocation
density near the GB, which was associated with an increase in the Von Mises
stress. In contrast, the dislocation pile-ups and the stress concentration were
less pronounced in the case of partially-transparent boundaries as the slip in
one grain can progress into the next grain with some degree of continuity. No
stress concentrations were found at these boundaries for fully-transparent
boundaries, and there was continuity of strain across the boundary, which is
not typical of most experimentally observed GBs. Simulations of ideal
bicrystals oriented for favorable slip transfer on the most highly favored slip
system in grains with high Schmid factors for slip transfer depends on the
number of active SS in operation in the neighborhood and that most boundaries
will lead to nearly opaque conditions while some boundaries will be
transparent. Finally, the model was applied to a particular experimentally
observed GB in which slip transfer was clearly operating indicating that the
model predicted a nearly transparent GB.
