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Local shear rearrangements in glassy systems : from micromechanics to structural relaxation in supercooled liquids

Abstract : In this thesis, the local yield stress method is applied and extended to study single, irreversible atomistic rearrangementsas well as structural relaxation in a model glass-forming liquid, a two dimensional binary Lennard-Jones mixture. Themethod gives access to the local mechanical response of an inherent configuration in a direct and non-perturbativemanner while controlling the length scales and loading directions. In the first part, the focus is on a small inclusion ofthe glass. Its micromechanical response is probed in the athermal quasi-static limit. The influence of the length scale,at which the mechanical response is probed, is discussed. The variation of the threshold statistics with the size of theprobing zone can be understood on the basis of a simple geometric argument and a weakest link assumption. Then, upondetermining the dependence of the local critical yield stress on the shear loading direction with a high angular resolution,it is observed that only a finite and discrete number of shear rearrangements is accessible, each of them having a distinctweak plane. Furthermore, the critical yield stress shows a high sensitivity towards the pressure in the simulation box. It isfound that for the length scale studied, a Mohr-Coulomb yield criterion describes piecewise accurately the critical shearstress. In the second part, a connection between structure and dynamics of model supercooled liquids is established. Thenovelty in the present work is the characterization of the structure through local slip thresholds. A strong correlation isfound between the stress barriers in the softest direction calculated in the as-quenched state and observables associatedto the relaxation of the liquid structure at parent temperature. As expected, a higher correlation coefficient is detected forliquids equilibrated at lower temperatures, as the potential energy landscape increasingly influences the dynamics.
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Submitted on : Friday, March 19, 2021 - 3:24:47 PM
Last modification on : Friday, August 5, 2022 - 11:54:23 AM


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Matthias Lerbinger. Local shear rearrangements in glassy systems : from micromechanics to structural relaxation in supercooled liquids. Physics [physics]. Université Paris sciences et lettres, 2020. English. ⟨NNT : 2020UPSLS006⟩. ⟨tel-03151944⟩



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