Dislocation Jamming and Andrade Creep

Abstract

We simulate the glide motion of an assembly of interacting dislocations under the action of an external shear stress and show that the associated plastic creep relaxation follows Andrade's law. Our results indicate that Andrade creep in plastically deforming crystals involves the correlated motion of dislocation structures near a dynamic transition separating a flowing from a jammed phase. Simulations in presence of dislocation multiplication and noise confirm the robustness of this finding and highlight the importance of metastable structure formation for the relaxation process.

Deblocking of interacting particle assemblies: from pinning to jamming

“…Dislocation multiplication favors the rearrangements of the system and induces a linear creep regime (flowing phase) at lower stress values, but it does not affect the initial powerlaw creep. The introduction of a finite effective temperature T had a similar effect [91]. The detailed analysis of the model data unveiled the dislocation microscopic dynamics in the Andrade, and in the stationary regimes: Most dislocations are arranged into metastable structures so that the stress field they generate in the material is screened out on large length-scales.…”

“…Shear yielding is thus another feature they have in common. As we will see in the following subsections, under stress conditions both soft materials [7] and crystalline solids [91] are susceptible to display jamming and shear yielding, due to the interactions and spatial arrangement of their constituent particles in the case of soft-matter systems, or to the interactions and spatial arrangement of their topological defects-such as dislocations-in plastically deforming crystals. Jamming and yielding could in turn be responsible for the remarkably similar creep and stationary flow rheology observed experimentally in these systems, in spite of the big differences among the materials involved.…”

“…[91], the temporal relaxation of a relatively simple dislocation dynamics model was studied through numerical simulation. In particular, a collection of parallel straight edge dislocations with Burgers vectors b i = bx moving in a single slip system under the action of constant stress was shown to give rise to Andrade-like creep at short and intermediate times for a wide range of applied stresses, without invoking thermally activated processes, i.e.…”

Micron-Scale Deformation: A Coupled In Situ Study of Strain Bursts and Acoustic Emission

“…In macroscopic samples, due to the large number of dislocations, the stress-strain response arXiv:1604.01815v1 [cond-mat.mtrl-sci] 6 Apr 2016 2 of the material is smooth allowing to predict the properties of the material with a high accuracy. In contrast, at the micrometer scale the inhomogeneity of the dislocation microstructure is in the order of the sample size resulting non-deterministic response due to the stochastic motion of dislocations [8][9][10][11][12] . So, in order to design new microscopic devices the mechanical properties of materials have to be described by a statistical approach at this scale.…”

“…The new fast micro-pillar fabrication procedure developed gives us the chance to perform a statistical analysis of the deformation processes. This is essential because during an individual compression experiment the stress varies intermittently (see below), 3 meaning that the dislocation system gives stochastic response to the acting force 11,14,16,27,28 . As a result of this defining material parameters from a unique measurement is impossible.…”