Creep control in soft particle packings

TL;DR

This study investigates creep behavior in soft sphere packings, revealing power-law creep with diffusive dynamics and exponential dependence on stress and hydrogel concentration, offering insights for controlling creep in soft solids.

Contribution

It provides the first detailed characterization of creep in soft granular packings, highlighting the exponential dependence on stress and confinement, and establishing scaling laws for creep behavior.

Findings

Creep persists up to large strains with power-law form.

Creep amplitude depends exponentially on applied stress.

Creep dynamics are influenced by hydrogel concentration.

Abstract

Granular packings display a wealth of mechanical features which are of widespread significance. One of these features is creep: the slow deformation under applied stress. Creep is common for many other amorphous materials such as many metals and polymers. The slow motion of creep is challenging to understand, probe and control. We probe the creep properties of packings of soft spheres with a sinking ball viscometer. We find that in our granular packings, creep persists up to large strains and has a power law form, with diffusive dynamics. The creep amplitude is exponentially dependent on both applied stress and the concentration of hydrogel, suggesting that a competition between driving and confinement determines the dynamics. Our results provide insights into the mechanical properties of soft solids and the scaling laws provide a clear benchmark for new theory that explains creep, and provide the tantalizing prospect that creep can be controlled by a boundary stress.