Dynamical heterogeneity in periodically deformed polymer glasses

2015

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The effect of a local shear transformation on plastic deformation of a three-dimensional amorphous solid is studied using molecular dynamics simulations. We consider a spherical inclusion, which is gradually transformed into an ellipsoid of the same volume and then converted back into the sphere. It is shown that at sufficiently large strain amplitudes, the deformation of the material involves localized plastic events that are identified based on the relative displacement of atoms before and after the shear transformation. We find that the density profiles of cage jumps decay away from the inclusion, which correlates well with the radial dependence of the local deformation of the material. At the same strain amplitude, the plastic deformation becomes more pronounced in the cases of weakly damped dynamics or large time scales of the shear transformation. We show that the density profiles can be characterized by the universal function of the radial distance multiplied by a dimensionless factor that depends on the friction coefficient and the time scale of the shear event.

Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Plastic deformation of a model glass induced by a local shear transformation

2015

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“…Interestingly, reversible avalanches of large particle displacements were observed at strain amplitudes below the critical value [17]. At finite temperatures, it was shown that the mean square displacement of particles exhibits a broad subdiffusive plateau during ten thousand cycles even at small strain amplitudes, and the relaxation process involves intermittent clusters of particles undergoing cage jumps [18,19].…”

Section: Introductionmentioning

confidence: 99%

Nonaffine rearrangements of atoms in deformed and quiescent binary glasses

2016

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The influence of periodic shear deformation on nonaffine atomic displacements in an amorphous solid is examined via molecular dynamics simulations. We study the three-dimensional Kob-Andersen binary mixture model at a finite temperature. It is found that when the material is periodically strained, most of the atoms undergo repetitive nonaffine displacements with amplitudes that are broadly distributed. We show that particles with large amplitudes of nonaffine displacements are organized into compact clusters. With increasing strain amplitude, spatial correlations of nonaffine displacements become increasingly long-ranged, although they remain present even in a quiescent system due to thermal fluctuations.

“…It was further shown that over many deformation cycles, the structural relaxation dynamics is spatially and temporally heterogeneous; namely, mobile particles, or cage jumps, tend to aggregate into transient clusters [10,14]. Furthermore, during cyclic shear near the yield strain, a cluster of atoms with large reversible nonaffine displacements induces a long-range, time-dependent elastic field that in turn might trigger secondary structural rearrangements.…”

Section: Introductionmentioning

confidence: 99%

Collective nonaffine displacements in amorphous materials during large-amplitude oscillatory shear

2017

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Using molecular dynamics simulations, we study the transient response of a binary LennardJones glass subjected to periodic shear deformation. The amorphous solid is modelled as the three-dimensional Kob-Andersen binary mixture at a low temperature. The cyclic loading is applied to slowly annealed, quiescent samples, which induces irreversible particle rearrangements at large strain amplitudes, leading to stress-strain hysteresis and a drift of the potential energy towards higher values. We find that the initial response to cyclic shear near the critical strain amplitude involves disconnected clusters of atoms with large nonaffine displacements. In contrast, the amplitude of shear stress oscillations decreases after a certain number of cycles, which is accompanied by the initiation and subsequent growth of a shear band.