Polycrystal aggregates subjected to plastic deformation exhibit changes in the yield stress and extended transients in the flow stress when they are reloaded along a different strain path. These effects (a well known one is the Bauschinger effect) are related to the rearrangement of the dislocation structure induced during previous loading. Here we present a dislocation-based hardening model that accounts for dislocation recombination and back-stresses, implement it in the polycrystal code VPSC, and simulate strain path changes in low carbon steel and in Mg AZ31. The path changes consist of tension followed by shear, and forward and reverse simple shear for the steel. In the case of Mg AZ31 we preload in tension along the rolling direction (RD) and reload in tension at different angles with respect to the RD. The results are compared to experimental data and highlight the role that directional dislocation structures induced during preload play during the reload stage.
We also discuss the use of this model for the interpretation of cruciform test results. The test allows us to impose arbitrary plane stress conditions and path changes, but the results are difficult to interpret in terms of constitutive response. Here we show that, when combined with Finite Element simulations, the crystal plasticity model provides a valuable tool for interpreting cruciform test results.