Characteristic stepwise strain hardening behaviour induced by slip and twinning of large-deformed copper single crystals: crystal plasticity modelling and simulation

The micromechanism-based stepwise strain hardening behaviour of copper single crystals significantly depends on the competition and collaboration between dislocation slip and deformation twinning. A crystal plasticity-based model of the strain hardening characteristics associated with slip and twinning interactions is proposed that focuses on modelling the stepwise strain hardening behaviour. An accumulated twin volume fraction is incorporated into the evolution of slip resistance to model slip-twinning (S-T) interactions at small strains. Then, the following stress fluctuation stage caused by the crystal reorientation is related to the twinning-twinning (T-T) interactions. Upon deformation to a large strain, a saturated hardening law including the slip-slip (S-S) interactions in the twinned region and the accumulated slip are presented. The effects of the initial crystal orientation and twinning on distinguished hardening stages are investigated. The stepwise strain hardening model reveals the dominating hardening mechanism at the initial hardening stage, which has been identified for orientation-dependent copper single crystals by investigating the slip and twinning increments. The stress fluctuation of a copper single crystal with a particular grain orientation can be described by introducing the evolution of the twin volume fraction and its saturation value, which allows an in-depth understanding of the evolution of large plastic deformation.