Generalized Constitutive Modeling of Granular Materials near the Flow-Arrest Transition

Flowing granular materials often abruptly arrest if not driven by sufficient applied stresses. Such abrupt cessation of motion can be economically expensive in industrial materials handling and processing, and is significantly consequential in intermittent geophysical phenomena such as landslides and earthquakes. However, the statistical and rheological properties of this nonequilibrium transition are not well-understood. We recently developed a fully stress-controlled granular simulation framework to elucidate such phenomena at the macroscopic bulk scale. Through extensive simulations, we construct a flow-arrest state diagram that clearly distinguishes between states of shear flow and arrest in granular materials in terms of their microstructural and rheological properties, and where interparticle friction is an important ingredient. Furthermore, granular flows in the vicinity of such a transition exhibit features that are not captured by the traditional rheological models, such as the presence of normal stress differences. I will describe our general tensorial constitutive model that suitably captures these features. The generality of the model will be demonstrated through its applicability in complex flow fields such as extensional and so-called triaxial flows, along with extensions to granular materials with enhanced compositional complexities such as large particle size dispersity.