Institut Charles Sadron Event

horaire: 11 h 00 Abstract: Amorphous solids are yield stress materials that can fail and flow when a sufficient shear stressis applied. The yielding transition occuring between the arrested state and the flowing regime is commonly accepted to be a critical phenomenon however the related exponents are not well understood, their universality is still under debate. During the past five years, a theoretical framework has been developed to make a link between the critical scaling of avalanches and the specific pseudogap form of the distribution of weak residual stresses P(x)?x ? [1,2]. Predictions of this theory, in particular the predominant role of the pseudogap exponent ?, have been directly verified by mesoscopic elasto-plastic models [1-3] and indirectly inferred by atomistic simulations [4]. However very recent results obtained with mesoscopic models have raised questions about the validity of the pseudogap description of P(x) in the stationary regime [5,6]. By combining atomistic simulations with the frozen matrix approach [7], we reveal the evolution of the local residual stress distribution in an amorphous packing upon deformation in the athermal quasi-static limit [8]. We find a pseudogap form P(x)?x ? in the freshly quenched state and in the early stages of deformation. After a few percent strain, however, P(x) starts to develop a plateau p 0 in the small x limit, where p 0 ?L ?p with L the system size. A direct comparison with the system size scaling of the stress drops shows that the statistical properties of avalanches are controlled by ? in the transient regime and the plateau exponent p in the steady state flow.