Elastic Granular Flows

Abstract:

The dry granular flowmap can be broken into two broad categories, the Elastic and the Inertial. Elastic flows are dominated by force chains and stresses are generated by the compression of the interparticle contacts within those chains, and thus are proportional to the stiffness of the contacts. The Elastic zone can be subdivided into two regimes, the Elastic-Quasistatic where forces are independent of the shear rate which at high shear rates transitions to Elastic-Inertial where the particle inertia is reflected in the forces and the stresses increase linearly with the shear rate. In the Inertial regime, the stresses vary with the square of the shear rate. It also is divided into two regimes, the Dense-Inertial where the flow is dominated by clusters of particles, and the Inertial-Collisional where the flow is dominated by binary collisions. Appropriately the elastic theory grew out of an old study of landslides.

But like most such studies, all of the above depend on idealized computer simulations of uniform sized spherical particles. Real particles are never round, never of uniform size, and the process of flowing changes surface properties and may even shatter the particles. But all indications are that real systems still fit into the pattern drawn out in the last paragraph. A grave problem facing the field is how to incorporate these effects without losing a fundamental understanding of the internal rheological processes.

This talk will begin with an overview of the Elastic flowmap and the behaviors associated with each flow regime. It will then discuss early work to include effects of particle shape and size mixtures and perhaps some effects of particle breakage.