  We use 2D numerical simulations to study dense suspensions of non-Brownian
hard particles using the Critical Load Model (CLM) under constant confining
pressures. This simple model shows discontinuous shear thickening (DST) as the
tangential forces get activated upon increased shear stresses. By
parameterizing a simple binary system of frictional and non-frictional
particles of different proportions we show that the jamming packing fraction,
at which the viscosity diverges, is controlled by the fraction of frictional
contacts. The viscosity of dense suspensions can thereby be expressed as a
function of the fraction of frictional contacts as well as the packing fraction
of solid particles. In addition, we show that there exists a simple
relationship between the fraction of frictional contacts and the two control
parameters (under confining pressure): the viscous number J and the ratio
between the repulsive barrier force and confining pressure. Under confining
pressures the viscosity curves are found to depend on the shear protocol, with
the possibility of yielding negative dynamic compressibility.
