Age-dependent transient shear banding in soft glasses

TL;DR

This paper investigates how transient shear bands form in soft glasses during startup shear, revealing that banding duration depends on shear rate and sample age, with implications for understanding flow behavior in these materials.

Contribution

It introduces numerical analysis of transient shear banding in soft glasses using two models, highlighting the role of stress overshoot and sample age in band formation and longevity.

Findings

Transient shear bands depend on shear rate and sample age.

Steady flow remains homogeneous despite transient banding.

Long-lived bands are associated with stress overshoot.

Abstract

We study numerically the formation of long-lived transient shear bands during shear startup within two models of soft glasses (a simple fluidity model and an adapted `soft glassy rheology' model). The degree and duration of banding depends strongly on the applied shear rate, and on sample age before shearing. In both models the ultimate steady flow state is homogeneous at all shear rates, consistent with the underlying constitutive curve being monotonic. However, particularly in the SGR case, the transient bands can be extremely long lived. The banding instability is neither `purely viscous' nor `purely elastic' in origin, but is closely associated with stress overshoot in startup flow.