Gulliver seminar, Giulio Biroli (ENS)

Lundi 21 juin 11:30-12:30 - Bibliothèque PCT - F3.04

How amorphous materials yield under stress : a new kind of out of equilibrium phase transition

I will show that a new kind of out of equilibrium phase transition is at the core of how amorphous solids yield in response to external deformations—a phenomenon that is crucial both for practical applications and for theoretical reasons. Such phase transition has strong connections with phenomena studied in the theory of disordered systems such as the zero-temperature spinodal of the Random Field Ising Model, the Depinning transition, and rare events.

Our results unveil that despite large differences in the materials' microscopic interactions and typical scales (from colloids to molecular glasses) a large degree of universality emerges as there are only two ways in which amorphous solids respond to a deformation : One, typical of well-annealed materials, is characterized by an abrupt failure with a macroscopic stress drop and the sudden emergence of sharp shear bands ; the other, typical of poorly annealed materials, shows merely a smooth crossover. By varying the preparation protocol, one can change the response of a given material from one to the other, and this change is controlled by a random critical point, akin to the one of the zero temperature Random Field Ising Model. We will confirm our scenario by molecular dynamics simulations, and by analytical and numerical analysis of elastoplastic models.