Gradient plasticity constitutive model reflecting the ultrafine micro-structure scale: the case of severely deformed copper

A further development of the mechanism-based strain gradient plasticity model well established in literature is reported. The major new element is the inclusion of the cell size effect in dislocation cell forming materials. It is based on a 'phase mixture' approach in which the dislocation cell interiors and dislocation cell walls are treated as separate 'phases'. The model was applied to indentation testing of copper severely pre-strained by equal channel angular pressing. The deformation behaviour and the intrinsic length scale parameter of the gradient plasticity model were related to the micro-structural characteristics, notably the dislocation cell size, resulting from the deformation history of the material.