Shear Banding of Soft Glassy Materials in Large Amplitude Oscillatory Shear

TL;DR

This paper demonstrates through simulations that soft glassy materials exhibit shear banding during large amplitude oscillatory shear, even at very low frequencies where homogeneous flow was expected, due to aging and rejuvenation dynamics.

Contribution

It reveals that shear banding occurs in soft glassy materials under LAOS across a wide range of conditions, including zero frequency, challenging previous assumptions about steady state flow.

Findings

Shear banding persists at low frequencies in LAOS.

Banding occurs even in materials that do not shear band under steady shear.

Flow behavior is governed by aging and rejuvenation cycles.

Abstract

We study shear banding in soft glassy materials subject to a large amplitude oscillatory shear flow (LAOS). By numerical simulations of the widely used soft glassy rheology model, supplemented by more general physical arguments, we demonstrate strong banding over an extensive range of amplitudes and frequencies of the imposed shear rate $\dot{\gamma}(t)=\dot{\gamma}_0\cos(\omega t)$, even in materials that do not permit banding as their steady state response to a steady imposed shear flow $\dot{\gamma}=\dot{\gamma}_0=$const. Highly counterintuitively, banding persists in LAOS even in the limit of zero frequency $\omega\to 0$, where one might a priori have expected a homogeneous flow response (consistent with the requirement of homogeneous flow for a strictly zero frequency steady imposed shear flow). We explain this finding in terms of an alternating competition within each cycle between glassy aging and flow rejuvenation. Our predictions have far-reaching implications for the flow behavior of aging yield stress fluids, suggesting a generic expectation of shear banding in flows of even arbitrarily slow time variation.