When do 2-D dislocations form cellular structures?

Simulations of pattern formation by edge dislocations in two dimensions are presented, with the aim of idenfying rha simplest type of model which spon taneously evolves dislocation cells and walls. The simulation program adds the forces on each dislocation due to all others, including the force due t o external stresses, applying periodic boundary conditions. In lieu of usin g a general force-velocity relationship, only the dislocation with the stro ngest force acting on it is moved during each step. Dislocation reactions a re given special treatment. Two runs are compared: one allowing two-dimensi onal mobility, i.e. climb as well as glide, and a second allowing only glid e but evolving through several cycles of external stress. A quantitative an alysis reveals dislocation walls in both cases, but shows that the latter r un, where each dislocation is limited to glide along a line? does nor exhib it well-defined dislocation cells. Future goals include introducing disloca tion sources, and developing continuum-type models capable of mimicking the dynamics observed. (C) 2001 Elsevier Science B.V. All rights reserved.