Simulation of High-Strain-Rate Comminution through a Breakage Model with Adaptive Rate Dependence

While laboratory evidence suggests that particle crushing generates nonnegligible rate-dependence in granular materials, few constitutive laws reproduce such effects in light of grain-scale fracture mechanisms. This paper presents a continuum breakage model with adaptive fluidity aimed at simulating seamlessly the compression of crushable sands across loading regimes spanning both quasi-static and dynamic conditions. For this purpose, the macroscopic fluidity of the material is modeled through concepts inspired by dynamic fracture mechanics and granular solid hydrodynamics. Specifically, the relationship between dynamic grain-scale processes and bulk dissipation relies on the evolution of a state variable linked to microscale entropy fluctuations, here referred to as breakage temperature. The model performance is assessed by reproducing the results of Split-Hopkinson bar compression tests conducted at different strain rates. It is shown that, compared to a correspondent viscous-breakage model characterized by stationary fluidity, the incorporation of adaptive rate-dependence leads to an improved model performance, in that it enables the compression/breakage response to be captured accurately without ad hoc adjustments of the viscous properties.