  We use a continuous mesoscopic model to address the yielding properties of
plastic composites, formed by a host material and inclusions with different
elastic and/or plastic properties. We investigate the flow properties of the
composed material under a uniform externally applied deviatoric stress. We show
that due to the heterogeneities induced by the inclusions, a scalar modeling in
terms of a single deviatoric strain of the same symmetry than the externally
applied deformation gives inaccurate results. A realistic modeling must include
all possible shear deformations. Implementing this model in a two-dimensional
system we show that the effect of harder inclusions is very weak up to
relatively high concentrations. For softer inclusions instead, the effect is
much stronger, even a small concentration of inclusions affecting the form of
the flow curve and the critical stress. We also present the details of a full
three dimensional simulation scheme, and obtain the corresponding results, both
for harder and softer inclusions.
