(398t) Rheology of Cohesive Granular Materials Across Multiple Dense Flow Regimes

Understanding flows of granular matter is essential for the design of particulate and gas-solid flow processes, and much research attention has been devoted to studying granular flows of non-cohesive particles.  However, cohesive particles are ubiquitous in nature and industrial processes and exhibit behaviors unseen in non-cohesive materials, including jamming at low packing fractions and agglomerate formation.  In this work, we study the rheology of cohesive granular material by performing discrete element simulations of homogeneous simple shear flow of assemblies of uniform, cohesive, spherical particles.  Cohesion is modeled as a van der Waals force between particles, and frictional and inelastic interactions are also considered.  To access multiple flow regimes, a wide array of cohesive strengths, particle volume fractions, and shear rates are simulated.  Dense shear flows of non-cohesive materials exhibit three regimes: (i) quasistatic regime, where the stress is independent of shear rate, (ii) inertial regime where the stress varies quadratically with shear rate and (iii) an intermediate regime where the stress manifests power-law dependence with n~1/2 [1]. Cohesion results in bifurcation of the inertial regime into two regimes whose boundaries are determined by a modified Bond number, which is a ratio of the van der Waals force to a characteristic contact force: (a) a new rate-independent regime and (b) an inertial regime. We present a rheological model for cohesive systems that captures all the simulation results.

[1]  S. Chialvo, J. Sun, and S. Sundaresan.  Phys. Rev. E 85, 021305 (2012).