  In particular types of layer- or lamellar-like microstructures such as
pearlite and lath martensite, plastic slip occurs favorably in directions
parallel to inter-lamellar boundaries. This may be due to the interplay between
morphology and crystallographic orientation or, more generally, due to
constraints imposed on the plastic slip due to the lamellar microstructural
geometry. This paper proposes a micromechanics based, computationally
efficient, scale independent model for particular type of lamellar
microstructures containing softer lamellae, which are sufficiently thin to be
considered as discrete slip planes embedded in a matrix representing the harder
lamellae. Accordingly, the model is constructed as an isotropic visco-plastic
model which is enriched with an additional orientation-dependent planar plastic
deformation mechanism. This additional mode is activated when the applied load,
projected on the direction of the soft films, induces a significant amount of
shear stress. Otherwise, the plastic deformation is governed solely by the
isotropic part of the model. The response of the proposed model is assessed via
a comparison to direct numerical simulations (DNS) of an infinite periodic
two-phase laminate. It is shown that the yielding behavior of the model follows
the same behavior as the reference model. It is observed that the proposed
model is highly anisotropic, and the degree of anisotropy depends on the
contrast between the slip resistance (or yield stress) of the planar mode
versus that of the isotropic part. The formulation is then applied to model the
substructure of lath martensite with inter-layer thin austenite films. It is
exploited in a mesoscale simulation of a dual-phase (DP) steel
microstructure.The results are compared with those of a standard isotropic
model and a full crystal plasticity model.
