Avalanches in crystal plasticity: from jamming to pinning

Recent microcrystal compression experiments, as well as acoustic emission studies of larger specimens, show that plastic, irreversible deformation is a highly fluctuating and intermittent process exhibiting e.g. power-law distributed strain bursts. The dominating mechanism of plastic deformation of crystalline solids is the stress-driven motion of dislocations, linear defects of the crystal lattice. The dislocations interact via long-range anisotropic stress fields and are constrained to move along a discrete set of glide planes dictated by the crystal structure, leading e.g. to the formation of complex, metastable dislocation structures, with deformation avalanches occurring as the system jumps from one metastable configuration to another: dislocations tend to jam, or stop their motion due to self-induced constraints. Additional complications may arise due to other defects in the material, acting as quenched pinning centers for the dislocations. Thus, in general one may expect the nature of the deformation process to be governed by the competition between "jamming" and "pinning" [1].

Here I will present an overview of our recent numerical studies of such phenomena using discrete dislocation dynamics (DDD) models of various kinds. A simple two-dimensional DDD model without additional defects gives rise to "glassy" avalanche dynamics with anomalous scaling properties, which we argue should originate from dislocation jamming [2]. Adding a sufficiently strong quenched pinning field interacting with the dislocations leads to fundamentally different avalanche dynamics, resembling that known in the context of depinning transitions of elastic manifolds in random media [3]. Finally, I'll also discuss our very recent results on three-dimensional DDD models.

[1] M. J. Alava, L. Laurson, and S. Zapperi, Crackling noise in plasticity,
Eur. Phys. J. Special Topics 223, 2353 (2014).

[2] P. D. Ispanovity, L. Laurson, M. Zaiser, I. Groma, S. Zapperi, and M. J. Alava,
Avalanches in 2D Dislocation Systems: Plastic Yielding Is Not Depinning,
Phys. Rev. Lett. 112, 235501 (2014).

[3] M. Ovaska, L. Laurson, and M. J. Alava, Quenched pinning and collective Dislocation Dynamics, Scientific Reports 5, 10580 (2015).