Peter Dusan Ispanovity

Abstract:

It is a long-standing challenge to reproduce numerically the appearance and evolution of the rich variety of dislocation patterns. In conventional two-dimensional models, although specific spatial correlations between dislocations always develop, typical dislocation structures seen in experiments do not seem to emerge. In the talk we demonstrate how two specific extensions of the 2D model lead to pronounced patterning. Firstly, the case of a non-linear elastic medium is considered, that is, quadratic terms are also taken into account in the stress-strain relation of the continuum the dislocations are embedded in. This extension naturally leads to an energy difference between the vacancy and interstitial type dislocation dipoles. The systematic inclusion of this phenomenon in the continuum theory of dislocations predicts the instability of the homogeneous dislocation structure, which is demonstrated by discrete dislocation dynamics simulations. Indeed, a specific pattern develops with a well-defined characteristic length-scale, resembling a structure seen experimentally in low-amplitude fatigue experiments. Secondly, the effect of dislocation climb is investigated. Introduction of a small climb mobility already leads to cell formation, that is, dislocation free regions are bounded by dislocation walls consisting of pure GNDs. The formation and subsequent growth of these cells are analogous to subgrain dynamics observed experimentally during recovery.