Topological constraints suppress shear localization in granular chain ensembles

TL;DR

This study demonstrates that granular chain ensembles with chains longer than four beads exhibit shear hardening and suppress shear localization, revealing how topological constraints influence flow and rigidity in granular materials.

Contribution

It provides experimental and simulation evidence that topological constraints in granular chains significantly alter shear behavior and localization, a novel insight into geometrically cohesive granular systems.

Findings

Chains longer than four beads show shear hardening.

Shear localization is suppressed in long chain ensembles.

Tensile forces and diffuse deformation regions are observed.

Abstract

Entangled granular systems exhibit mechanical rigidity and resistance to deformation, reminiscent of cohesive materials, due to their reduced degrees of freedom and contact friction. A quantitative understanding of how classical granular phenomena, such as shear localization and plastic flow, appear in such geometrically cohesive systems remains unknown. Here, we investigate this using granular chain ensembles subjected to direct shear tests. Our experiments reveal that chains longer than four beads exhibit pronounced shear hardening, which is nearly independent of the applied normal stress and is accompanied by the complete suppression of shear localization. The volume dilation of the long chain ensembles also does not vanish in the steady state. We complement this phenomenology, which is distinct from that of typical frictional granular ensembles, with DEM simulations. The simulations reveal that tensile forces are generated due to particles being locally jammed, characterized by a high non-covalent coordination number. Consequently, this leads to a deformation that shows a very diffuse region of localization and enhanced shear hardening. Overall, our study highlights that granular chains provide a systematic route to map how connectivity constraints impact flow properties and mechanical rigidity.