Micro-macro transition and simplified contact models for wet granular materials

TL;DR

This study uses discrete particle simulations to connect micro-scale liquid bridge parameters with macro-scale properties like cohesion and torque in wet granular materials, providing simplified models for better understanding.

Contribution

It introduces a correlation between micro-parameters and steady state cohesion, and demonstrates that a simplified linear model can effectively replicate complex liquid bridge behavior.

Findings

Micro parameters influence macroscopic cohesion and torque.

A correlation links liquid bridge rupture distance and maximum adhesive force to cohesion.

Simplified linear models can replicate nonlinear liquid bridge behavior.

Abstract

Wet granular materials in a quasi-static steady state shear flow have been studied with discrete particle simulations. Macroscopic quantities, consistent with the conservation laws of continuum theory, are obtained by time averaging and spatial coarse-graining. Initial studies involve understanding the effect of liquid content and liquid properties like the surface tension on the macroscopic quantities. Two parameters of the liquid bridge contact model have been studied as the constitutive parameters that define the structure of this model (i) the rupture distance of the liquid bridge model, which is proportional to the liquid content, and (ii) the maximum adhesive force, as controlled by the surface tension of the liquid. Subsequently a correlation is developed between these micro parameters and the steady state cohesion in the limit of zero confining pressure. Furthermore, as second result, the macroscopic torque measured at the walls, which is an experimentally accessible parameter, is predicted from our simulation results as a dependence on the micro-parameters. Finally, the steady state cohesion of a realistic non-linear liquid bridge contact model scales well with the steady state cohesion for a simpler linearized irreversible contact model with the same maximum adhesive force and equal energy dissipated per contact.