Microstructure evolution was largely dominated by the internal stress fields that appeared upon the appearance of inhomogeneous structures in a material. The hardening behavior of metals physically originates from such a complex microstructure evolution. As deformation proceeds, statistically homogeneous distributions of dislocations in grains became unstable, which constitutes the driving force for the development of a pronounced dislocation sub-structure. The dislocation structure already appeared at early stages of deformation due to the statistical trapping of dislocations. Cell walls contained dislocation dipoles and multipoles with high dislocation densities and enclose cell-interior regions with a considerably smaller dislocation density. The presence and evolution of such a dislocation arrangement in the material influenced the mechanical response of the material and was commonly associated with the transient hardening after strain path changes. This contribution introduces a micro mechanical continuum model of the dislocation cell structure based upon the physics of the dislocation interactions. The approximation of the internal stress field in such a microstructure and the impact on the macroscopic mechanical response were the main items investigated here.

Microstructural Instabilities - Dislocation Substructures with Pronounced Mechanical Effects. M.G.D.Geers, E.M.Viatkina, W.A.M.Brekelmans: Philosophical Magazine, 2006, 86[21-22], 3161-73