Stress localization, stiffening and yielding in a model colloidal gel

TL;DR

This study uses simulations to explore how a model colloidal gel stiffens and yields under shear, revealing stress localization, network breaking, and structural reorganization during deformation.

Contribution

It provides a detailed analysis of stress localization and network failure mechanisms in colloidal gels under shear, combining numerical simulations with space-resolved stress analysis.

Findings

Stress localization leads to network node breaking at ~30% strain.

Stiffening results from chain stretching and alignment.

Large-scale structural reorganization occurs at yielding.

Abstract

We use numerical simulations and an athermal quasi-static shear protocol to investigate the yielding of a model colloidal gel. Under increasing deformation, the elastic regime is followed by a significant stiffening before yielding takes place. A space-resolved analysis of deformations and stresses unravel how the complex load curve observed is the result of stress localization and that the yielding can take place by breaking a very small fraction of the network connections. The stiffening corresponds to the stretching of the network chains, unbent and aligned along the direction of maximum extension. It is characterized by a strong localization of tensile stresses, that triggers the breaking of a few network nodes at around 30% of strain. Increasing deformation favors further breaking but also shear-induced bonding, eventually leading to a large-scale reorganization of the gel structure at the yielding. At low enough shear rates, density and velocity profiles display significant spatial inhomogeneity during yielding in agreement with experimental observations.