A micro mechanical finite element model to compute the overall instantaneous stiffness of fiber-reinforced composites in elastic-plastic response is presented. The model is applicable to a periodic diamond array of elastic circular fibers embedded in an elastoplastic matrix subjected to a plane stress loading. This model enforces symmetry and anti-symmetry conditions isolating the smallest unit cell and should greatly increase the speed of doing "built-inn micromechanics within a larger finite element program because of the small number of degrees of freedom (12 to 14 d.o.f.). The matrix plastic behavior is modeled using the endochronic theory without a yield surface. Various off-axis elastoplastic characteristics predicted by the mini grid for a boron/aluminum composite are presented. Comparison with experimental data and a fine grid finite element solution shows very good agreement and demonstrates the effectiveness of the mini model presented. / Master of Science