A crystal plasticity model of a formation of a deformation band structure

Abstract

The formation of deformation bands with the typically alternating sign of the misorientation across their boundaries is interpreted as spontaneous deformation instability caused by anisotropy of hardening. To analyse the nature of the fragmentation, a model of a rigid-plastic crystal domain deformed by symmetric double slip in a plane-strain compression is considered. The basic reason for the deformation band existence is that a local decrease in number of active slip systems in the bands is energetically less costly than a homogeneous deformation by multislip. However, such model of the bands predicts their extreme orientation and their width tends to zero. This trend is modified by hardening caused by a build up of the band boundaries and by a dislocation bowing (Orowan) stress. The model provides an explanation of observed orientation of the bands, their width and the significant change in the structural morphology seen as the band reorientation occurs at large strains. The predictions are in a favourable agreement with the available observations.