Rheology of wet granular materials in shear flow: experiments and discrete simulations

The behaviour of wet granular media in shear flow is characterized by the dependence of apparent friction μ * and solid fraction Φ S on the reduced pressure P * and the inertia number I. Reduced pressure, P * = σ 22 a 2 /F 0 , compares the applied normal stress σ 22 on grains of diameter a to the tensile strength of contact F 0 (proportional to the surface tension Γ of the liquid and the beads diameter). A specifically modified rotational rheometer is used to characterize the response of model wet granular material (beads with diameter of submillimetric range) to applied shear rate γ under controlled normal stress σ 22 . Discrete Element Method (DEM) simulations in 3D are carried out in parallel and numerical results are compared with experimental ones. As P * is reduced, an increase of the apparent friction coefficient μ * = σ 12 / σ 22 , measured in the critical state and in slow flows with inertial effects is observed. While the agreement between experiments and simulations is good for dry materials as well as for wet materials in the quasistatic limit ( I →0), some differences appear at finite I , for which some possible origins are discussed.