Application of a substructure-based hardening model to copper under loading path changes

In addition to texture, plastic anisotropy of a polycrystalline fcc metal stems from the directional nature of the dislocation substructure within individual grains. This produces the marked work hardening or softening observed immediately following load path changes. Following the framework of Peeters et al.,([1.2]) in bcc steel, we develop a dislocation substructure evolution-based stage III hardening model for copper, capable of capturing the constitutive response under load path changes. The present model accounts for the more complicated substructure geometry in fcc metals than in bee. Using an optimization algorithm, the parameters governing substructure evolution in the model are fit to experimental stress-strain curves obtained during compression along the three orthogonal directions in samples previously rolled to various reductions. These experiments approximate monotonic, reverse, and cross-load paths. With parameters suitably chosen, the substructure model, embedded into a self-consistent polycrystal plasticity model, is able to reproduce the measured flow stress response of copper during load path change experiments. The sensitivity of the parameters to the assumed substructure geometry and their uniqueness are also discussed.