Flow-Arrest Transition in Granular Materials*

Flowing granular materials can abruptly arrest if the applied stresses are smaller than a friction-dependent critical value. Such a phenomenon is commonly observed in geophysical scenarios and industrial practice, often with deleterious consequences. However, the statistical and rheological properties of this non-equilibrium transition are not well-understood. In this talk, I will describe our stress-controlled granular simulations that indicate a highly stochastic nature of this transition with long-tailed distributions of flowing times before arrest, which diverge as a power law at a critical stress ratio. We construct a flow-arrest state diagram that clearly distinguishes between shear flow and shear arrest in granular systems in terms of microstructural and rheological properties, with inter-particle friction being an important ingredient. Furthermore, granular flows in the vicinity of this transition exhibit rheological features that are not captured by the traditional μ(I) model, such as the presence of normal stress differences. I will describe our recently developed 3D constitutive model that captures these features and is fully compatible with more complex flow scenarios beyond simple shear, such as extensional and so-called triaxial flows.