The microplastic behavior of several MMC is investigated by means of t
ension and compression tests. This behavior is assymetric : the propor
tional limit is higher in tension than in compression but the work har
dening rate is higher In compression. These differences ate analysed i
n terms of maxium of the Tresca's shear stress at the interface (propo
rtional limit) and of the emission of dislocation loops during the coo
ling (work hardening rate). On another hand, a model is proposed to ca
lculate the value of the yield stress, describing the composite as a m
aterial composed of three phases : inclusion, unaffected matrix and ma
trix surrounding the inclusion having a gradient in the density of the
thermally induced dilocations.