Physical origin of shear-banding in jammed systems

TL;DR

This paper proposes a simple physical model explaining why some jammed systems develop shear bands while others do not, based on the ratio of relaxation to restructuring times.

Contribution

It introduces a minimal approach linking shear-banding to the ratio of relaxation and restructuring times in jammed systems.

Findings

Shear-banding occurs when relaxation time is shorter than restructuring time.

Homogeneous flow is observed when the relaxation time exceeds restructuring time.

The model explains the physical origin of shear-banding in jammed materials.

Abstract

Jammed systems all have a yield stress. Among these materials some have been shown to shear-band but it is as yet unclear why some materials develop shear-band and some others do not. In order to rationalize existing data concerning the flow characteristics of jammed systems and in particular understand the physical origin of such a difference we propose a simple approach for describing the steady flow behaviour of yield stress fluids, which retains only basic physical ingredients. Within this frame we show that in the liquid regime the behaviour of jammed systems turns from that of a simple yield stress fluid (exhibiting homogeneous flows) to a shear-banding material when the ratio of a characteristic relaxation time of the system to a restructuring time becomes smaller than 1, thus suggesting a possible physical origin of these trends.