Strain Bursts and Dislocation Avalanches in Obstacle-Hardened Materials*

We develop a hybrid continuum-discrete model for the collective dynamics of dislocations in dense obstacle fields. The density of obstacles is described by continuum conservation equations, and solved numerically. With this hybrid model, we unravel the mystery of how and why irradiation-induced defects enhance or inhibit strain bursts in submicron single crystals. It is shown that smaller strain burst amplitudes in irradiated nano- and micro-pillars are obtained under stress control conditions. However, under strain control conditions, bursts are found not to be sensitive to irradiation, despite the arresting effect of radiation defects. This feature is a result of rapid stress relaxation truncating the strain burst, compared with the influence of irradiation-induced defects. The influence of dislocation-defect interaction mechanisms, cross slip, irradiation dose, as well as loading mode on strain bursts is systematically investigated, and the results compared with experimental observations. We also present results showing the relationship to spatial localization of plastic flow.