  We discuss the plastic behavior of an amorphous matrix reinforced by hard
particles. A mesoscopic depinning-like model accounting for Eshelby elastic
interactions is implemented. Only the effect of a plastic disorder is
considered. Numerical results show a complex size-dependence of the effective
flow stress of the amorphous composite. In particular the departure from the
mixing law shows opposite trends associated to the competing effects of the
matrix and the reinforcing particles respectively. The reinforcing mechanisms
and their effects on localization are discussed. Plastic strain is shown to
gradually concentrate on the weakest band of the system. This correlation of
the plastic behavior with the material structure is used to design a simple
analytical model. The latter nicely captures reinforcement size effects in
$-(\log N/N)^{1/2}$ observed numerically. Predictions of the effective flow
stress accounting for further logarithmic corrections show a very good
agreement with numerical results.
