Quantitative study of the rheology of frictional suspensions: Influence of friction coefficient in a large range of viscous numbers

The rheology of dense suspensions is studied by discrete-element method simulation, focusing on the interplay of the solid fraction, confining pressure, shear rate, and viscosity. Using a minimal model based on lubrication and contact forces, we are able to recover experimental results available in the literature, in a very large range of solid fractions. We show that bulk friction is only weakly dependent on contact friction when a normalized shear rate, the so-called viscous number I-v is kept constant. In contrast, contact friction has a strong influence on the jamming solid fraction (empty set)(m). We provide empirical proof that all the rheology could be accounted for using I-v and phi/phi(m). By separating the contributions of lubrication and contact forces on the total shear stress, it is shown that contacts dominate at a solid fraction above 0.77 of jamming solid fraction. Universal expressions of macroscopic friction and solid fraction as functions of the viscous number are finally offered.