This talk focuses on several aspects of plasticity of heterogeneous metallic materials. We first consider complications in processes of averaging statistical phenomena such as effects of heterogeneity and dislocation-barrier interactions to the macroscale. We briefly discuss the origins and interpretations of back stress in polycrystals and multiphase alloys, leading to the understanding that explanations based on “hard” and “soft” regions, whether local or nonlocal, are not fully adequate. We re-examine the form of the multiplicative decomposition of the deformation gradient for metallic polycrystals and suggest a way of describing the associated multi-scale incompatibility fields, with and without damage (Clayton and McDowell, 2003a, 2003b). Based on recent collaborative work (Clayton et al., 2004), finite strain kinematics are proposed for various types of crystalline defects (point, translational dislocations, rotational dislocations (disclinations) and general Somogliana dislocations). Finally, the scale dependence of net geometrically necessary dislocation and disclination density is explored; it is suggested that gradients of net dislocation density give rise to long range internal stress fields that affect slip.
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