Yielding and Strain Stiffening in Entangled Assemblies of Frictional Granular Chains

TL;DR

This study explores how interparticle friction influences the nonlinear rheology of granular chain packings, revealing nonmonotonic stress responses and enhanced strain stiffening due to entanglements and interlocking effects.

Contribution

It demonstrates the significant impact of friction and chain structure on yielding and strain stiffening in granular chains, contrasting with molecular polymer behavior.

Findings

Maximum stress varies nonmonotonically with friction coefficient.

Interlocking events increase strain stiffening.

Gaps between grains promote entanglements and shear zone broadening.

Abstract

Packings of macroscopic granular chains capture some of the essential aspects of molecular polymer systems and have been suggested as a paradigm to understand the physics on a molecular scale. However, here we demonstrate that the interparticle friction $\mu$ in granular chain packings, which has no counterpart in polymer systems, leads to a nontrivial yielding and rheological response. Based on discrete element simulations we study the nonlinear rheology of random packings of granular chains under large amplitude oscillatory shear. We find that the maximum stress and the penetration depth of the shear deformation into the material bulk are nonmonotonic functions of friction with extrema at intermediate values of $\mu$. We also show that the regularly repeated gaps between the adjacent grains, which are special to commercial granular chains, broaden the shear zone and enhance the entanglements in the system by promoting the interlocking events between chains. These topological constraints can significantly increase the degree of strain stiffening. Our findings highlight the differences between the physics of granular chain packings and molecular polymer systems.