It was recalled that, in deformed crystals, long-range internal stresses developed during deformation as a result of heterogeneity of the dislocation distribution; which frequently formed a cell structure. The composite model described these internal stresses in terms of the elastic/plastic strain mismatch between hard cell-walls and soft cell-interiors. This mismatch was closely related to a well-defined density of so-called interface dislocations at the hard/soft region interfaces. The interface dislocations were geometrically necessary. According to the composite model, their main role was to provide the internal stresses which were required for the simultaneous and compatible deformation of the hard and soft regions. The interface dislocations did not, in general, contribute to the flow stress and their density did not appear explicitly in the flow-stress equation. It was shown that this was strictly true for single-slip deformation. In the case of multiple slip, a different situation existed because some of the interface dislocations of one glide system could act as forest dislocations to glide dislocations of another slip system. This situation was analyzed for a simple model cell structure. It was found that interaction of the glide dislocations with interfacial forest dislocations made only a negligible contribution to the overall flow stress. This was true for both glide dislocations bowing into, and for glide dislocations bowing out of, the walls.

The Effect of Geometrically Necessary Dislocations on the Flow Stress of Deformed Crystals Containing a Heterogeneous Dislocation Distribution. H.Mughrabi: Materials Science and Engineering A, 2001, 319-321, 139-43