Internal motion of soft granular particles under circular shearing: Rate-dependent quaking and its spatial structure

TL;DR

This study investigates how soft granular particles under circular shear exhibit rate-dependent quaking phenomena, revealing different spatial structures and dynamics at various shear rates through 3D particle tracking.

Contribution

It introduces a circular shear cell setup and demonstrates the role of shear rate in the emergence and structure of quaking in soft granular particles, confirming previous findings and proposing a unifying shear rate parameter.

Findings

Quaking occurs at intermediate shear rates with large particle displacements.

At low shear rates, system-spanning clusters with substructures form.

High shear rates produce smooth particle motions.

Abstract

Tightly packed granular particles under shear often exhibit intriguing intermittencies, specifically, sudden stress drops that we refer to as quaking. To probe the nature of this phenomenon, we prototype a circular shear cell that is capable of imposing a uniform and unlimited shear strain under quasi-static cyclic driving. Spherical PDMS(polydimethylsiloxane) particles, immersed in fluid, are driven in a fixed total volume at a wide range of shear rates, with particle trajectories captured in 3D space via refraction-index-matched fluorescent tomography. Statistics on the magnitude of fluctuating displacements of individual particles shows distinct dependence on the shear rate. Particle motions are smooth at high shear rates. At intermediate shear rates, quaking emerges with clusters of particles exhibiting relatively large displacements. At low shear rates, a cluster can span the entire system. and the cluster exhibits substructures in view of localized particle movements. Overall, we have confirmed that the quaking phenomena in the current setup are consistent with our previous work [Phys. Rev. Lett.,126, 128001 (2021)], and that the dimensionless shear rate that we have proposed [Phys. Rev. Research 6, 023065 (2024)] is indeed a good parameter for unifying the transitions observed in different experimental geometries.