Nonaffine deformation under compression and decompression of a flow-stabilized solid

TL;DR

This study investigates how micron-scale particles in flow-stabilized solids deform under compression and decompression, revealing the roles of non-affine motion, jamming proximity, and the asymmetry in response times.

Contribution

The paper introduces experimental insights into particle-scale deformation, highlighting the decay of non-affine responses and the asymmetry between compression and decompression effects in flow-stabilized solids.

Findings

Non-affine deformation decays with distance from the free surface.

Compression induces more particle rearrangements than decompression.

Deformation response time is shorter under compression than decompression.

Abstract

Understanding the particle-scale transition from elastic deformation to plastic flow is central to making predictions about the bulk material properties and response of disordered materials. To address this issue, we perform experiments on flow-stabilized solids composed of micron-scale spheres within a microfluidic channel, in a regime where particle inertia is negligible. Each solid heap exists within a stress gradient imposed by the flow, and we track the positions of particles in response to single impulses of fluid-driven compression or decompression. We find that the resulting deformation field is well-decomposed into an affine field, with a constant strain profile throughout the solid, and a non-affine field. The magnitude of this non-affine response decays with the distance from the free surface in the long-time limit, suggesting that the distance from jamming plays a significant role in controlling the length scale of plastic flow. Finally, we observe that compressive pulses create more rearrangements than decompressive pulses, an effect that we quantify using the $D^2_\mathrm{min}$ statistic for non-affine motion. Unexpectedly, the time scale for the compression response is shorter than for decompression at the same strain (but unequal pressure), providing insight into the coupling between deformation and cage-breaking.