Relationship between interparticle contact lifetimes and rheology in gravity-driven granular flows

The validity of the Bagnold constitutive relation in gravity-driven granular flow down an inclined plane is studied by discrete element (DEM) simulations. In the limit of infinitely hard particles, the Bagnold relation is known to hold exactly. We determine deviations from this relation as a function of all parameters governing interparticle interactions. These include elastic compliance, inelastic dissipation, friction coefficient, and interparticle cohesion. We find significant deviations from Bagnold rheology in some regions of this parameter space and propose a generalized Bagnold relation to account for this effect. Moreover, we note a significant correlation between the breakdown of Bagnold rheology in the bulk and the appearance of a long-time tail in the two-particle contact time distributions.