Effective friction of granular flows made of non-spherical particles

Abstract

Abstract. Understanding the rheology of dense granular matter is a long standing problem and is important both from the fundamental and the applied point of view. As the basic building blocks of granular materials are macroscopic particles, the nature of both the response to deformations and the dissipation is very different from that of molecular materials. In the absence of large gradients, the best approach formulates the constitutive equation as an effective friction: for sheared granular matter the ratio of the off-diagonal and the diagonal elements of the stress tensor depends only on dynamical parameters, in particular the inertial number. In this work we employ numerical simulations to extend this formalism to granular packings made of frictionless elongated particles. We measured how the shape of the particles affects the effective friction, volume fraction and first normal stress difference, and compared it to the spherical particle case. We had to introduce polydispersity in particle size in order to keep the systems of the more elongated particles disordered.

Shear-driven flow of athermal, frictionless, spherocylinder suspensions in two dimensions: Spatial structure and correlations

“…7(c) and 7(d) for a bidisperse system, we see that in the monodisperse system the peaks in both the x and y directions are more sharply defined and persist out to considerably longer length scales. Similar results have been suggested in simulations comparing monodisperse and polydisperse spherocylinders in three dimensions, for a model in which energy dissipation is by inelastic particle collisions rather than the viscous drag we use here [23].…”

Flow and rheology of frictional elongated grains

“…The length, time and mass units of the simulation were set implicitly by setting the mean particle diameter 2R, density ρ and contact stiffness k (equal for the normal and tangential force) to unity. To prevent crystallization for frictionless particles [36], especially at larger values of α, we used size polydispersity of 10% (standard deviation to mean ratio in a uniform distribution). While crystallization was less critical for frictional particles, we kept the polydispersity fixed for consistency.…”

Rheological response of nonspherical granular flows down an incline

“…Recent numerical studies on two-and three-dimensional (2D and 3D) systems of frictional dumbbells yielded increasing effective friction with increasing particle elongation in chute flows, as well as in a Couette shear cell [46,47]. Another numerical study with frictionless spherocylinders in 3D resulted in a nonmonotonic but predominantly decreasing effective friction as a function of the particle aspect ratio in Couette shear [50,51].…”