Application of the taylor polycrystal plasticity model to complex deformation experiments

The extended Taylor assumption of uniform deformation gradient among grains was applied in 3-D polycrystal plasticity simulations for complex loading paths at finite strain for OFHC Cu using the Los Alamos polycrystal plasticity (LApp) code (Kocks et al, 1994). Comparisons of both stress-strain behavior and texture evolution, with and without the inclusion of latent hardening effects, show that the theory overpredicts the rate of development of texture in both torsion and compression. Compression stress-strain behavior was accurately predicted, but the effect of the prestrain, either compressive or torsional, on subsequent nonproportional deformation response was inadequately modeled. Some possible sources of the discrepancies are discussed, including the low order nature of the extended Taylor model for intergranular interactions as compared to self-consistent models, low order formulation of slip system hardening, lack of accounting for formation of dislocation substructure within grains, and the possible role of anisotropic elasticity. Deformation-induced anisotropy and accommodation of intergranular constraint afforded by geometrically necessary dislocation substructure formation is viewed as the key neglected element of the formulation.