# Long-term memory and delayed shear localisation in soft glassy materials

## TL;DR

This paper investigates how soft glassy materials exhibit long-term memory effects leading to sudden shear localization and stress drops, even long after initial deformation, through theoretical modeling and simulations.

## Contribution

It introduces a theoretical framework showing that long-term memory in soft glassy materials causes delayed shear localization and catastrophic instability.

## Key findings

- Shear localization can occur long after initial strain application.
- Stress drops are associated with heterogeneous strain fields.
- Long-term memory effects are crucial for understanding material failure.

## Abstract

We study theoretically the dynamics of soft glassy materials during the process of stress relaxation following the rapid imposition of a shear strain. By detailed numerical simulations of a mesoscopic soft glassy rheology model and three different simplified continuum fluidity models, we show that a dramatic shear localisation instability arises, in which the strain field suddenly becomes heterogeneous within the sample, accompanied by a precipitous drop in the stress. Remarkably, this instability can arise at extremely long delay times after the strain was applied, due to the long-term memory inherent to glassy systems. The finding that a catastrophic mechanical instability can arise long after any deformation could have far reaching consequences for material processing and performance, and potentially also for delayed geophysical phenomena.