Oscillatory athermal quasistatic deformation of a model glass

Abstract

We report computer simulations of oscillatory athermal quasi-static shear deformation of dense amorphous samples of a three dimensional model glass former. A dynamical transition is observed as the amplitude of the deformation is varied: for large values of the amplitude the system exhibits diffusive behavior and loss of memory of the initial conditions, whereas localization is observed for small amplitudes. Our results suggest that the same kind of transition found in driven colloidal systems is present in the case of amorphous solids (e.g. metallic glasses). The onset of the transition is shown to be related to the onset of energy dissipation. Shear banding is observed for large system sizes, without, however, affecting qualitative aspects of the transition.Understanding the behavior of materials under mechanical deformation is of primary importance for many contexts. While the deformation behavior of crystals is theoretically well understood, no universally accepted framework exists to rationalize the behavior of mechanically driven amorphous systems, although significant progress has been made in recent years in developing a detailed understanding of how an amorphous solid responds to external stresses [1][2][3]. Considerable recent activity has been spurred by an interest in the mechanical behavior of metallic glasses, soft glassy materials, foams and granular packings, and has involved theoretical, computational and experimental investigations [2,[4][5][6][7][8]. Particular interest is understandably focused on the manner in which the response of an amorphous solid changes from nearly elastic response at small applied stress to a state of flow for large applied stress.Many computational investigations have employed the approach of studying the zero temperature behavior of amorphous solids under quasi static conditions (using an Athermal Quasi Static or AQS procedure [9]). In this procedure, systems are kept in local energy minimum configurations, or inherent structures [10,11] while varying the strain. In previous work on model systems of binary Lennard-Jones particles, it has been shown that upon monotonically increasing the applied shear strain, the inherent structures evolve towards energies corresponding to the limit of high temperatures [12]. This and related phenomena are referred to as rejuvenation, in contrast to the well studied process of ageing whereby (typically) a glassy material descends to deeper energy configurations as a function of the waiting time over which it relaxes at a given temperature. In contrast, when a cycle of strain is applied up to a maximum value which is then reversed [13], both ageing and rejuvenation are observed, with small amplitude strains found to reduce the energy of samples ("overage" them), while larger amplitude strains tend more often to increase the energy (thus "rejuvenating" the samples). Initial conditions of the samples in such cases matter: samples with lower initial potential energy are rejuvenated more easily than those with higher energy [13].In a very ...

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

“…We also comment that the transition from reversible dynamics at γ 0 = 0.07 to the plastic regime at γ 0 = 0.08 occurs at higher strain amplitudes than the critical value γ 0 = 0.06 reported in the previous MD study [10], where simulations were performed at the higher oscillation frequency ωτ = 0.02 and higher temperature T LJ = 0.1 ε/k B . At the same time, our results are in agreement with the critical strain amplitude γ 0 = 0.07, which marks the onset of energy dissipation and particle diffusion in a binary glass under oscillatory athermal quasistatic shear deformation [11,17].…”

Plasticity of a Colloidal Polycrystal under Cyclic Shear

“…Similarly to the case of continuous shear, the microscopic dynamics in cyclically deformed amorphous solids have been found to be diffusive (or even subdiffusive), in simulations [18,19] as well as in experiments on colloids [2,20] or granular matter [21,22]. Aging effects have been reported for macroscopic quantities, e.g.…”

A microscopic view of the yielding transition in concentrated emulsions

“…[25][26][27][28][29][30] A first point to keep in mind is that no fully reversible state is actually observed here, since even at the lowest applied strains some dynamics are observed. This is also true, at least on a finite time scale, for most of the work on systems of interacting particles where the existence of a reversible regime was advocated.…”