Examination of the microscopic definition for granular fluidity

Recent work has used an introduced property, termed granular fluidity (defined as the shear rate divided by the stress ratio), to help quantify and model nonlocal behavior within granular flows. A so-called microscopic definition was subsequently proposed which links this granular fluidity to the packing fraction, particle diameter, and the granular temperature. This definition provides a physical basis on which the nature of granular fluidity can be understood. Here we have examined the microscopic definition, first replicating the previously demonstrated behavior using DEM simulations of shear cells and then demonstrating that the relationship's coefficients are dependent on the coefficient of friction, the presence of tangential damping, and the presence of rolling resistance. When the geometry is changed from a shear cell to a cylindrical hopper, the relationship shifts away from the expected response, thus demonstrating that there are geometry dependent effects that are not captured by the original formulation. This shows that granular fluidity is more complex than previously thought and that the current microscopic definition is insufficient.

Automated summary

Recent research has used granular fluidity to model nonlocal behavior within granular flows, proposing a microscopic definition linking it to packing fraction, particle diameter, and granular temperature. The study found that granular fluidity is more complex than previously thought, and the current microscopic definition is insufficient to capture its behavior.