Origin of two distinct stress relaxation regimes in shear jammed dense suspensions

TL;DR

This study investigates the particle-scale dynamics of shear jammed dense suspensions, revealing two distinct stress relaxation regimes linked to localized plastic events and dilation, with implications for understanding shear jamming.

Contribution

It uncovers the underlying particle-scale mechanisms of stress relaxation in shear jammed suspensions, highlighting the role of localized plastic events and dilation in the process.

Findings

Discovered a non-exponential stress relaxation with a sharp discontinuous drop at high stresses.

Confirmed that localized plastic events cause the stress discontinuity.

Linked transient relaxation behavior to the steady state shear jamming phase diagram.

Abstract

Many dense particulate suspensions show a stress induced transformation from a liquid-like state to a solid-like shear jammed (SJ) state. However, the underlying particle-scale dynamics leading to such striking, reversible transition of the bulk remains unknown. Here, we study transient stress relaxation behaviour of SJ states formed by a well-characterized dense suspension under a step strain perturbation. We observe a strongly non-exponential relaxation that develops a sharp discontinuous stress drop at short time for high enough peak-stress values. High resolution boundary imaging and normal stress measurements confirm that such stress discontinuity originates from the localized plastic events, whereas, system spanning dilation controls the slower relaxation process. We also find an intriguing correlation between the nature of transient relaxation and the steady state shear jamming phase diagram obtained from the Wyart-Cates Model.