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

Abstract

Wet granular materials in a quasistatic steadystate 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 identified as the constitutive parameters that influence the macroscopic rheology (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 microparameters 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 with the same dependence on the microparameters. 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. B Sudeshna Roy

Effect of cohesion on local compaction and granulation of sheared soft granular materials

“…Split-Bottom Ring Shear Cell: We use MercuryDPM [4,5], an open-source implementation of the Discrete Particle Method, to simulate a shear cell with annular geometry and a split bottom plate, as explained in [6]. Earlier studies used similar rotating set-ups, including [7,8].…”

“…Thus, the shear band remains far away from the inner wall. The inter-particle friction coefficient is μ p = 0.01 and other parameters are detailed in [6].…”

“…We use a linear visco-elastic frictional contact model in combination with Willet's capillary bridge model [3,6,10]. In order to see the effect of varying cohesive strength on the macroscopic rheology of wet materials, we vary the intensity of the maximum capillary force f max cap = πdσ cos θ, by varying the surface tension of the liquid σ, while keeping the volume of liquid bridges constant, (V b = 75 nl), corresponding to a liquid saturation of 8% of the voidage.…”

“…The macroscopic quantities are obtained by spatial coarse graining with temporal averaging of the system in steady state as detailed in [6,10]. We study the effect of the above mentioned dimensionless numbers on the local volume fraction φ in the critical state [10].…”

From Particles in Steady State Shear Bands via Micro-Macro to Macroscopic Rheology Laws

“…[1][2][3]5,6]. With attractive forces involved, like van-der Waals forces or liquid-bridges, this leads to cohesion added on top of the already non-trivial dynamics of granular matter [2,[6][7][8]. Dependent on the energy input (e.g.…”