Full three dimensional numerical cell model analyses are carried out for a metal reinforced by short fibers, to study the development of ductile matrix failure. A porous ductile material model is used to describe the effect of the nucleation and growth of voids to coalescence. In each case studied the computations are continued through the mechanically unstable regime, where an open crack forms near the ends of the fibers by the coalescence of voids in the matrix. Comparison of predictions for an isotropic hardening model and a kinematic hardening model are used to evaluate the effect of a metal that forms a rounded vertex on the yield surface. The full three dimensional model is used to study effects of deviations from equal transverse tension in directions perpendicular to the fibers. (C) 1998 Acta Metallurgica Inc.