Statistical modelling of dislocation systems

The paper discusses fluctuation phenomena in plastic flow. It is demonstrated that dislocation motion in materials with high dislocation mobility is characterized by large velocity fluctuations that lead to an intrinsically intermittent dynamics on microscopic and mesoscopic scales even if macroscopic deformation is stable and homogeneous. The large fluctuations indicate that the dislocation system in a deforming crystal is close to a critical point (‘yielding transition’). For motion of isolated dislocations through weak obstacle fields, this critical point corresponds to the depinning transition of an elastic manifold. A phenomenological approach to modelling the influence of collective, intermittent dislocation motions on dislocation microstructure evolution is discussed. Applications include the development of misorientations in dislocation cell structures and the interplay of strain hardening and dislocation patterning under deformation conditions where fractal dislocation arrangements are formed.