Atomic scale.    First I used a numerical simulation approach at the atomistic scale on a model polydisperse and bidisperse Lennard-Jones glass. The choice of this simple type of model was justified by the ambition to describe the generic features of all glassy materials, foams, colloids, metallic glasses, granulars...Therefore the model system must reproduce the complexity of these materials without introducing each of their specificities.
The numerical simulations of the shear of the glassy material quenched well below its glass transition temperature are realised either by a quasistatic, athermal simulation with an opti- mized method of potential energy minimization (PEM) or by non-equilibrium molecular dynamics (NEMD) at low temperature. One of the success of my work was to clarify the controversial issue of the physical validity of the PEM method by showing that both methods yield similar results in the limit of low temperature and shear rate of NEMD [3].
Figure 4: The individual atoms/grains in a typical binary system and the digitized floe boundaries in the summer sea ice pack.
The configurations so obtained have ex- hibited a macroscopical stress-strain me- chanical response in accordance with what is observed experimentally in glassy mate- rials in the quasistatic deformation regime, where one can distinguish a linear part as- sociated to a few sparse localized quadrupo- lar plastic rearrangements (also called shear transformation zones) followed above a criti- cal strain by the so-called plastic part where a large number of irreversible events occurs and forms through a cascade mechanism mi- croscopic shear bands that relax the stress macroscopically. Consequently through this elasto-plastic mechanisms the glass reaches a steady state in which the elastic energy intro- duced in the system by the external load is dissipated internally by these localized plas-
tic catastrophes. A fine study of the local rearrangements showed that under very slow shear rate the mechanical response of the glass is strongly heterogeneous, with strong spatiotemporal fluctuations in the velocity profile, in agreement with recent experimental observations in giant micellar surfractant as well as in granular systems or foams. I also analysed the evolution of the local stress components and showed that the local shear component could be described by a Levy flight process originating from the uncorrelated sum of quadrupolar events [5].