Dislocation avalanches

[1] In metallic glass, it can be observed via shear banding with stress localization;[2] and single crystal plasticity, it shows up as slip burst.

[9][1] Although evidence of intermittent flow behavior is long known and studied, it is not until past two decades that a quantitative understanding of the phenomenon is developed with help of novel experimental techniques.

[10][11] The amplitudes of the acoustic signals can be related to the area swept by the fast-moving dislocations and hence to the energy dissipated during deformation events.

To resolve this issue, Sparks et al. has designed an experiment to measure first fracture of Si beam and compare with theoretical prediction to determine the respond speed of the system.

During these in-situ tests, a constant voltage was applied during the deformation experiment to record current evolution during intermittent plastic flow.

Result shows that indentation tip remains contact with the sample throughout experiments, which proves the respond speed is fast enough.

A possible explanation this discrepancy is based on different moving speed of edge and screw dislocations in two type of crystals.

Based on this explanation, we will also expect a direction dependence of avalanche events in HCP crystals, which currently lack in experimental data.