Granular rheology near jamming and engineering models

We investigate the rheology of dry granular materials via molecular dynamics simulations of homogeneous, simple shear flows of soft, frictional, noncohesive spheres. In this presentation, we will show that three flow regimes exist 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. The particle-softness effect on the variation of shear stress ratio with respect to inertia number will be demonstrated. We also propose a rheological model that blends the asymptotic relations in each regime to obtain a general description for these flows. Finally, a constitutive model incorporating microstructure evolution will be shown to be able to predict the complex rheology of rate-independent flows.