The effect of coupled friction and adhesion on the rheology of non-Brownian dense suspensions

The role of adhesion between particles on the rheology of non-Brownian frictional suspensions undergoing simple shear flow is investigated numerically. To this purpose, we use two different numerical methods, namely, the force-coupling method and the fictitious domain method. The intensity of adhesion, volume fraction, and friction coefficient are separately varied. The parameter space to be explored is first constrained by analyzing particle depletion and shear-banding phenomena near the bounding walls under conditions of low volume fraction and applied stress. It is then shown that the relative viscosity of the suspension is a function of both volume fraction ϕ and shear stress Σ12. The variation of the viscosity with these two parameters may be understood in the usual frame of suspension jamming, provided that the friction-dependent maximum volume fraction ϕmμ, now depends on the dimensionless suspension stress σ∗=6πΣ12a12/Fadh that involves the adhesive force between particles Fadh and the particle radius a1. The variation of the maximum volume fraction with stress may be interpreted as the variation of the yield stress with volume fraction. This curve separates the plane (ϕ,σ∗) into two regions: one in which the suspension flows and the other in which it does not. The contribution of contact forces to normal stresses is also investigated. Its behavior differs markedly from that of nonadhesive particle suspensions, especially at moderate volume fractions.