# Unsteady flow, clusters and bands in a model shear-thickening fluid

## TL;DR

This paper investigates the complex unsteady flow behaviors, including clusters and bands, in a 2D model of shear-thickening granular fluids near jamming, revealing large-scale patterns and their dynamics.

## Contribution

It uncovers the formation and dynamics of large-scale flow patterns like bands and clusters in shear-thickening granular fluids, highlighting their dependence on strain rate.

## Key findings

- Large-scale patterns depend on strain rate.
- Force chains form giant bands at lower stress.
- Clusters extend along dilational direction at higher stress.

## Abstract

We analyse the flow curves of a two-dimensional assembly of granular particles which are interacting via frictional contact forces. For packing fractions slightly below jamming, the fluid undergoes a large scale instability, implying a range of stress and strainrates where no stationary flow can exist. Whereas small systems were shown previously to exhibit hysteretic jumps between the low and high stress branches, large systems exhibit continuous shear thickening arising from averaging unsteady, spatially heterogeneous flows. The observed large scale patterns as well as their dynamics are found to depend on strainrate: At the lower end of the unstable region, force chains merge to form giant bands that span the system in compressional direction and propagate in dilational direction. At the upper end, we observe large scale clusters which extend along the dilational direction and propagate along the compressional direction. Both patterns, bands and clusters, come in with infinite correlation length similar to the sudden onset of system-spanning plugs in impact experiments.