Self-induced marginality in plastically deformed crystals

Quasibrittle plastic yielding is a salient feature of well-annealed glassy materials. We show that a similar mechanical response is characteristic of perfect crystals after they experience mechanically-induced massive nucleation of dislocations. We argue that such ‘preparation’ effectively converts a mechanically crystalline sample into a mechanically pseudoamorphous one. To understand the nature of the associated transformation we study a model 2D crystal subjected to AQS driving. We show that pristine crystals ‘primed’ in this way exhibit both pre- and postyield dislocation avalanches with power-law statistics. The value of the computed exponents is indicative of self-induced marginal stability. Our main tool is the novel mesoscopic tensorial model (MTM) of crystal plasticity representing a conceptual trade-off between continuum and atomic descriptions. It captures the specificity of crystals with different lattice symmetry at relatively low computational cost while relying minimally on phenomenology. Rather strikingly, MTM allows one to deal with a statistically meaningful number of dislocations while accounting in a geometrically exact way for finite deformations. The obtained results challenge the prevailing opinion that crystal and amorphous plasticity are fundamentally different phenomena. As MTM does not deal with dislocations directly, our work reinforces the idea that in both cases it is the elastic incompatibility which evolves through intermittent avalanches.