Softening induced instability of a stretched cohesive granular layer

TL;DR

This paper investigates a surface instability in a stretched cohesive granular layer caused by strain softening, revealing a universal mechanism applicable to systems with negative stress sensitivity to strain.

Contribution

It introduces a simple model linking strain softening to surface instability in cohesive granular materials under tension.

Findings

Cellular pattern forms spontaneously on the granular surface.

Strain softening above a critical strain triggers the instability.

The mechanism is applicable to systems with negative stress sensitivity.

Abstract

We report on a cellular pattern which spontaneously forms at the surface of a thin layer of a cohesive granular material submitted to in-plane stretching. We present a simple model in which the mechanism responsible of the instability is the ``strain softening'' exhibited by humid granular materials above a typical strain. Our analysis indicates that such type of instability should be observed in any system presenting a negative stress sensitivity to strain perturbations.