Probing relevant ingredients in mean-field approaches for the athermal rheology of yield stress materials

TL;DR

This paper investigates the role of mechanical noise in the non-linear rheology of athermal yield stress materials, showing that local stress exhibits normal diffusion proportional to plastic activity, which can inform mean-field models.

Contribution

It demonstrates that mechanical noise induces normal diffusion in local stress, with a density-independent proportionality to plastic activity, linking microscopic dynamics to rheological flow curves.

Findings

Local stress exhibits normal diffusion under mechanical noise.

Diffusion constant is proportional to mean plastic activity.

Proportionality constant is density independent.

Abstract

Although the notion of mechanical noise is expected to play a key role in the non-linear rheology of athermally sheared amorphous systems, its characterization has so far remained elusive. Here, we show using molecular dynamic simulations that in spite of the presence of strong spatio-temporal correlations in the system, the local stress exhibits normal diffusion under the effect of the mechanical noise in the finite driving regime. The diffusion constant appears to be proportional to the mean plastic activity. Our data suggests that the corresponding proportionality constant is density independent, and can be directly related to the specific form of the rheological flow curve, pointing the way to a generic way of modeling mechanical noise in mean-field equations.