Geometrically necessary dislocations and strain gradient plasticity––a dislocation dynamics point of view

The relations between mesoscopic plastic strain gradients, ‘geometrically necessary’ dislocations (GND), and dislocation dynamics are discussed. It is argued that the connection between GND and size effects in crystal plasticity should be established on the basis of dislocation dynamics, taking into account the specific deformation conditions. It is demonstrated that dislocation dynamics based models for size effects lead to different phenomenological forms of gradient plasticity ‘laws’ proposed in the literature.