Signatures of shear thinning-thickening transition in dense athermal shear flows

TL;DR

This study uses molecular dynamics simulations to identify clear signatures of the transition from shear thinning to shear thickening in dense athermal shear flows, highlighting changes in granular temperature, anisotropy, and particle dynamics.

Contribution

The paper introduces a novel set of signatures, including anisotropy and scaling behaviors, to detect the shear thinning-thickening transition in dense athermal systems.

Findings

Shear thickening occurs when the derivative of ln(T_g) with respect to ln(γ̇) exceeds 2.

At the transition, the pair distribution function shows maximum anisotropy.

Distinct scaling behaviors of MSD and relaxation time characterize the transition.

Abstract

In non-equilibrium molecular dynamics simulations of dense athermal shear flows, we observe the transition from shear thinning to shear thickening at a crossover shear rate $\dot\gamma_c$. Shear thickening occurs when $\frac{{\rm d (ln} T_g)}{{\rm d (ln}\dot\gamma)}>2$ with $T_g$ the granular temperature. At the transition, the pair distribution function shows the strongest anisotropy. Meanwhile, the dynamics undergo apparent changes, signified by distinct scaling behaviors of the mean squared displacement and relaxation time on both sides of $\dot\gamma_c$. These features serve as robust signatures of the shear thinning-thickening transition.