UC Santa Cruz

Granular materials are central to a wide range of earth science processes. The majority of granular flow rheology experiments and theory describes flows composed of smooth spheres, but natural shear flows are composed of particles exhibiting a range of irregular shapes, sizes, and material properties. For natural hazards involving granular media, like landslides and earthquakes, it is important to understand how the complexity of natural grains affects the transition between nearly static slow moving shear flow regimes and dilatational fast moving shear flow regimes. The transition between these end member regimes can take many forms and occur over orders of magnitude of velocity and pressure conditions. Integrating an understanding of the effects of different material properties and grain shape into velocity phase regimes will allow for a complete energy balance to be drawn up for granular shear flow. Such an understanding will result in effective predictions of rheological behavior based on certain material characteristics and boundary conditions and will answer an enduring and fundamental physics question of how energy entering into a granular system is dissipated. I develop a new method for measuring fluctuation energy in granular shear flow experiments with acoustic energy, and I use this method to examine how internally induced vibrations affect the mechanics of transitional regime flows and the dependence of these mechanics on the material properties of the solid grains that make up the flow. I find that grain shape and material capacity for plastic damage can change how energy is dissipated in a shear flow, which in turn affects the overall rheology of the system.