Rheology of wet granular materials in shear flow: experiments and discrete simulations
Résumé
The behaviour of wet granular media in shear flow is characterized by the dependence of apparent friction μ* and solid fraction ΦS on the reduced pressure P* and the inertia number I. Reduced pressure, P*= σ22a2/F0, compares the applied normal stress σ22 on grains of diameter a to the tensile strength of contact F0 (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 σ22. 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*=σ12/σ22, 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.