- The effect of plasticity on the growth of a crack originating in an elastic solid across an interface and into an elastic-viscoplastic solid is analyzed numerically. The analyses are carried out within a framework where the continuum is characterized by two constitutive relations; one relating the stress and strain in the bulk material and the other relating the traction and separation across a specified set of cohesive surfaces. Crack initiation, crack growth and crack arrest arise naturally as a consequence of the imposed loading, without a priori assumptions concerning criteria for crack growth and for crack path selection. Full transient analyses are carried out. Various values of initial flow strength and cohesive strength of the elastic-viscoplastic solid and of cohesive strength of the interface are considered. With the ratio of cohesive strength of the elastic-viscoplastic solid to cohesive strength of the interface fixed, increasing the ratio of cohesive strength to initial flow strength for the elastic-viscoplastic solid is found to promote crack deflection into the interface.