Unilateral interactions in granular packings: A model for the anisotropy modulus

TL;DR

This paper introduces a simplified model for granular materials that captures how unilateral interparticle interactions influence elastic responses, including anisotropy, during quasi-static shear deformations.

Contribution

It presents a new model deriving constitutive relations with three elastic moduli, highlighting the role of anisotropy modulus related to shear and volumetric strains.

Findings

Anisotropy modulus scales with shear and volumetric strain ratio.

Bulk and shear moduli are independent of deformation when scaled by contact density.

Model predictions agree qualitatively with simulations away from jamming transition.

Abstract

Unilateral interparticle interactions have an effect on the elastic response of granular materials due to the opening and closing of contacts during quasi-static shear deformations. A simplified model is presented, for which constitutive relations can be derived. For biaxial deformations the elastic behavior in this model involves three independent elastic moduli: bulk, shear, and anisotropy modulus. The bulk and the shear modulus, when scaled by the contact density, are independent of the deformation. However, the magnitude of the anisotropy modulus is proportional to the ratio between shear and volumetric strain. Sufficiently far from the jamming transition, when corrections due to non-affine motion become weak, the theoretical predictions are qualitatively in agreement with simulation results.