Abstract: In this paper, the 3-D composite constitutive model proposed in Reference1 is extended to analyze finite elasto-plastic deformation. Constitutive equations and explicit incremental stiffness tensors for the Updated Lagrangian solution and the Total Lagrangian solution are derived and used to predict the nonuniform and localized deformation of ductile single crystals subjected to tensile loading. The obtained results are in good agreement with the experimental data2 and predictions of previous crystal th...