Nanomechanics of slip avalanches in amorphous plasticity

Cao, Penghui; Dahmen, Karin A.; Kushima, Akihiro; Wright, Wendelin J.; Park, Harold S.; Short, Michael P.; Yip, Sidney

doi:10.1016/j.jmps.2018.02.012

Cited by 47 publications

(23 citation statements)

References 52 publications

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“…6, somewhat resembling the serrations in compression experiments. Such fluctuations have also been observed in previous simulations of Cu-Zr system 29 and Lennard-Jones systems 44 . By checking the relative displacement of two reference atoms on either side of the shear band, we found the sliding speed of the shear band also fluctuates.…”

Section: Monotonic Deformation Processsupporting

confidence: 84%

Atomistic origin of stress overshoots and serrations in a CuZr metallic glass

2018

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In this work we use molecular dynamics simulations to study the stress overshoots of metallic glass Cu50Zr50 in three scenarios (unloading-reloading, slide-stop-slide, and stress serrations) that are associated with shear band relaxation. We found that, after the elastic recovery effect is factored out, atomic volume in the shear band barely changes during compressive relaxation but decreases during tensile relaxation, while local fivefold symmetry increases consistently for both cases. We propose that the atomistic mechanism for the related stress overshoots is due to the relaxation of structural symmetry, instead of free volume, in the shear band. Upon unloading, a propagating shear band continues for some time before arrested, which results in a stress undershoot and could contribute to material fatigue under cyclic elastic loads. We did not directly observe stress serrations via molecular dynamics simulations due to the very high simulated strain rates. While athermal quasistatic simulations produce serrated flow stress, we note that such serrations result from global avalanches of shear events rather than the relaxation of the shear band.

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Section: Monotonic Deformation Processsupporting

confidence: 84%

Atomistic origin of stress overshoots and serrations in a CuZr metallic glass

2018

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“…4(a) indicates that incident avalanches with larger magnitudes will, in general, result in a broader noise distribution. We noted similar trends in a model metallic glass where the cross-over behavior was associated with the interplay between small and large events [19]. The data collapse in Fig.…”

Section: Particle Displacement Statisticssupporting

confidence: 71%

Self-diffusion in plastic flow of amorphous solids

Karimi

2019

Phys. Rev. E

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We report on a particle-based numerical study of sheared amorphous solids in the dense slow flow regime. In this framework, deformation and flow are accompanied by critical fluctuation patterns associated with the macroscopic plastic response and single particle kinematics. The former is commonly attributed to the collective slip patterns that relax internal stresses within the bulk material and give rise to an effective mechanical noise governing the latter particle-level process. In this work, the avalanche-type dynamics between plastic events is shown to have a strong relevance on the self-diffusion of tracer particles in the Fickian regime. As a consequence, strong size effects emerge in the effective diffusion coefficient that is rationalized in terms of avalanche size distributions and the relevant temporal occurrence.

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“…On the modeling side, much of this can be traced back to differences in which the stress redistribution after a local plastic event is treated, i.e., to different treatments of the mesoscale dynamics [11]. When a relaxing volume element increases the stress on all neighboring elements, as happens in the presence of shear bands in, e.g., bulk metallic glasses and granular materials on larger scales, a mean field exponent τ = 3/2 is found [12,13]. When, instead, stress redistribution takes the form of a quadrupolar kernel derived from Eshelby's work for localized plastic zones in elastic media [14], the exponent reduces to approximately τ = 1.3 in three-dimensional systems in the absence of slip localization [15,16].…”

Section: Introductionmentioning

confidence: 99%

Transforming Mesoscale Granular Plasticity Through Particle Shape

2019

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When an amorphous material is strained beyond the point of yielding it enters a state of continual reconfiguration via dissipative, avalanche-like slip events that relieve built-up local stress. However, how the statistics of such events depend on local interactions among the constituent units remains debated. To address this we perform experiments on granular material in which we use particle shape to vary the interactions systematically. Granular material, confined under constant pressure boundary conditions, is uniaxially compressed while stress is measured and internal rearrangements are imaged with x-rays. We introduce volatility, a quantity from economic theory, as a powerful new tool to quantify the magnitude of stress fluctuations, finding systematic, shape-dependent trends. In particular, packings of flatter, more oblate shapes exhibit more catastrophic plastic deformation events and thus higher volatility, while rounder and also prolate shapes produce lower volatility. For all 22 investigated shapes the magnitude s of relaxation events is well-fit by a truncated power law distribution P (s) ∼ s −τ exp(−s/s * ), as has been proposed within the context of plasticity models. The power law exponent τ for all shapes tested clusters around τ = 1.5, within experimental uncertainty covering the range 1.3 -1.7. The shape independence of τ and its compatibility with mean field models indicate that the granularity of the system, but not particle shape, modifies the stress redistribution after a slip event away from that of continuum elasticity. Meanwhile, the characteristic maximum event size s * changes by two orders of magnitude and tracks the shape dependence of volatility. Particle shape in granular materials is therefore a powerful new factor influencing the distance at which an amorphous system operates from scale-free criticality. These experimental results are not captured by current models and suggest a need to reexamine the mechanisms driving mesoscale plastic deformation in amorphous systems. arXiv:1808.06271v3 [cond-mat.soft]

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Nanomechanics of slip avalanches in amorphous plasticity

Cited by 47 publications

References 52 publications

Atomistic origin of stress overshoots and serrations in a CuZr metallic glass

Atomistic origin of stress overshoots and serrations in a CuZr metallic glass

Self-diffusion in plastic flow of amorphous solids

Transforming Mesoscale Granular Plasticity Through Particle Shape

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