  Plastic yield of amorphous solids occurs by power law distributed slip
avalanches whose universality is still debated. Determination of the power law
exponents from experiments and molecular dynamics simulations is hampered by
limited statistical sampling. On the other hand, while existing elasto-plastic
depinning models give precise exponent values, these models to date have been
limited to a scalar approximation of plasticity which is difficult to reconcile
with the statistical isotropy of amorphous materials. Here we introduce for the
first time a fully tensorial mesoscale model for the elasto-plasticity of
disordered media that can not only reproduce a wide variety of shear band
patterns observed experimentally for different deformation modes, but also
captures the avalanche dynamics of plastic flow in disordered materials. Slip
avalanches are characterized by universal distributions which are
quantitatively different from mean field predictions, both regarding the
exponents and regarding the form of the scaling functions, and which are
independent of system dimensionality (2D vs 3D), boundary and loading
conditions, and uni-or biaxiality of the stress state. We also measure average
avalanche shapes, which are equally universal and inconsistent with mean field
predictions. Our results provide strong evidence that the universality class of
plastic yield in amorphous materials is distinct from that of mean field
depinning.
