  We investigate the rheology of granular materials via molecular dynamics
simulations of homogeneous, simple shear flows of soft, frictional, noncohesive
spheres. In agreement with previous results for frictionless particles, we
observe three flow regimes existing in different domains of particle volume
fraction and shear rate, with all stress data collapsing upon scaling by powers
of the distance to the jamming point. Though this jamming point is a function
of the interparticle friction coefficient, the relation between pressure and
strain rate at this point is found to be independent of friction. We also
propose a rheological model that blends the asymptotic relations in each regime
to obtain a general description for these flows. Finally, we show that
departure from inertial number scalings is a direct result of particle
softness, with a dimensionless shear rate characterizing the transition.
