Microscopic origins of shear stress in dense fluid-grain mixtures

Donia Marzougui (1, 2) , Bruno Chareyre (1, 2) , Julien Chauchat (3)

1 3SR - Laboratoire sols, solides, structures - risques [Grenoble]
2 GéoMécanique
3 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]

A numerical model is used to simulate rheome-ter experiments at constant normal stress on dense sus-pensions of spheres. The complete model includes sphere-sphere contacts using a soft contact approach, short range hydrodynamic interactions defined by frame-invariant expressions of forces and torques in the lubrication approximation , and drag forces resulting from the porome-chanical coupling computed with the DEM-PFV technique. Series of simulations in which some of the coupling terms are neglected highlight the role of the porome-chanical coupling in the transient regimes. They also reveal that the shear component of the lubrication forces, though frequently neglected in the literature, has a dominant effect in the volume changes. On the other hand, the effects of lubrication torques are much less significant. The bulk shear stress is decomposed into contact stress and hydrodynamic stress terms whose dependency on a dimensionless shear rate-the so called vis-cous number I v-are examined. Both contributions are increasing functions of I v , contacts contribution dominates at low viscous number (I v <0.15) whereas lubrication contributions are dominant for I v > 0.15, consistently with a phenomenological law infered by other authors. Statistics of microstructural variables highlight a complex interplay between solid contacts and hydro-dynamic interactions. In contrast with a popular idea, the results suggest that lubrication may not necessarily reduce the contribution of contact forces to the bulk shear stress. The proposed model is general and applies directly to sheared immersed granular media in which pore pressure feedback plays a key role (triggering of avalanches, liquefaction). Keywords granular suspension · rheology · lubrication · shear flow · discrete element method · hydromechanical coupling 2 Donia Marzougui et al.

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des solides [physics.class-ph]

Donia Marzougui, Bruno Chareyre, Julien Chauchat. Microscopic origins of shear stress in dense fluid-grain mixtures. Granular Matter, 2015, 17, pp.297 - 309. ⟨10.1007/s10035-015-0560-6⟩. ⟨hal-01399568⟩