Structural aging of a cohesive and amorphous granular solid under cyclic loading

TL;DR

This study explores how cyclic loading causes aging in a cohesive granular raft at an air-oil interface, leading to increased strength and stiffness but reduced ductility, with structural evolution driven by particle dynamics around voids.

Contribution

It reveals the aging process of a cohesive granular raft under cyclic loading and its effects on mechanical properties and structure, which was previously not well understood.

Findings

Cyclic loading increases packing fraction logarithmically.

Aged rafts exhibit higher strength and stiffness.

Structural heterogeneity decreases with cyclic aging.

Abstract

We investigate how cyclic loading evolves the structure and deformation behaviors of a granular raft composed of particles floating at an air-oil interface. The raft has a disordered particle packing structure, and is cohesive due to capillary interactions between particles. Under uniaxial cyclic loading with a small strain amplitude, the raft's packing structure experiences an aging process characterized by logarithmically increasing packing fraction and decreasing structural heterogeneity. The observed structural change is due to particle dynamics that are organized around morphologically evolving voids in the raft. The raft is then subjected to quasi-static tension or compression tests until failure. In comparison with non-aged rafts, the rafts that experienced cyclic loading show a higher strength, higher stiffness, and lower ductility, along with qualitatively different features, such as a stress overshoot in the loading curve.