Effect of collisional elasticity on the Bagnold rheology of sheared frictionless two-dimensional disks.

We carry out constant volume simulations of steady-state, shear-driven flow in a simple model of athermal, bidisperse, soft-core, frictionless disks in two dimensions, using a dissipation law that gives rise to Bagnoldian rheology. Focusing on the small strain rate limit, we map out the rheological behavior as a function of particle packing fraction ϕ and a parameter Q that measures the elasticity of binary particle collisions. We find a Q^{*}(ϕ) that marks the clear crossover from a region characteristic of strongly inelastic collisions, Q<Q^{*}, to a region characteristic of weakly inelastic collisions, Q>Q^{*}, and give evidence that Q^{*}(ϕ) diverges as ϕ→ϕ_{J}, the shear-driven jamming transition. We thus conclude that the jamming transition at any value of Q behaves the same as the strongly inelastic case, provided one is sufficiently close to ϕ_{J}. We further characterize the differing nature of collisions in the strongly inelastic vs weakly inelastic regions, and recast our results into the constitutive equation form commonly used in discussions of hard granular matter.