Energetic approach to subgrain formation

A variational formulation of the incrementally linear rigid-plastic approximation to crystal plasticity is set up. It is shown that the subgrain formation is a consequence of a tendency to minimize the sum of the incremental dissipated energy and the incremental energy that is related to the increase of flow stress. A physically motivated nonlocal formulation of the variational problem leads to a finite size of the subgrains formed. A crystal deformed by symmetric double slip is considered as an example.