Yielding and microstructure in a 2D jammed material under shear deformation

TL;DR

This study investigates how microstructural changes in a 2D jammed material under cyclic shear relate to its macroscopic yielding behavior, revealing a yield point characterized by structural conservation or rearrangement.

Contribution

It introduces a microstructural method to identify the yield point in a 2D jammed material without rheological measurements, linking microscopic rearrangements to macroscopic yield.

Findings

Below yield, the structure remains conserved over time.

Above yield, the structure continually rearranges.

The yield strain matches rheological measurements.

Abstract

The question of how a disordered material's microstructure translates into macroscopic mechanical response is central to understanding and designing materials like pastes, foams and metallic glasses. Here, we examine a 2D soft jammed material under cyclic shear, imaging the structure of ~50,000 particles. Below a certain strain amplitude, the structure becomes conserved at long times, while above, it continually rearranges. We identify the boundary between these regimes as a yield strain, defined without rheological measurement. Its value is consistent with a simultaneous but independent measurement of yielding by stress-controlled bulk rheometry. While there are virtually no irreversible rearrangements in the steady state below yielding, we find a largely stable population of plastic rearrangements that are reversed with each cycle. These results point to a microscopic view of mechanical properties under cyclic deformation.