The relations between mesoscopic plastic strain gradients, `geometrically necessary' dislocations, and dislocation dynamics were discussed. It was argued that the connection between geometrically necessary dislocations and size effects in crystal plasticity should be established on the basis of dislocation dynamics, taking into account the specific deformation conditions. It was demonstrated that dislocation dynamics based models for size effects led to different phenomenological forms of gradient plasticity `laws' proposed in the literature.

Geometrically Necessary Dislocations and Strain Gradient Plasticity - a Dislocation Dynamics Point of View. M.Zaiser, E.C.Aifantis: Scripta Materialia, 2003, 48[2], 133-9