A Laboratory for Naturalistic Granular Flows
Abstract
Understanding granular flows has direct implications for civil engineering, transport and landscape evolution. 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. Integrating an understanding of the effects of different material properties and grain shape into the transition between nearly static, slow moving shear flow regimes and dilatational, fast moving shear flow regimes will allow for both an energy balance to be drawn up for granular shear flow and effective predictions of rheological behavior. We have developed and successfully used new methods and experiments to reveal fundamental differences in how grains of differing shape and composition both create and respond to acoustic perturbation during shear in dry and saturated settings, with and without wide-scale grain breakage. Armed with these new methods, we require new instrumentation to best answer the remaining question of how grain strength and shape affects granular material shear flows. (1) A new TA Instruments Discovery Hybrid Rheometer HR-2 will allow for top of the line rheological assessment. The Discovery series of rheometers employs a new magnetic bearing that reduces in-instrument friction by 70%. This is the only such bearing on the marker. Our new methods were developed using a used TA Instruments AR2000ex rheometer acquired in 2009. Our custom geometries will transfer easily to the updated Discovery model, allowing us to measure rotor torque and thus frictional strength of granular materials with much higher degree of accuracy. Furthermore, the Discovery series offers a new Tribo-Rheometry system that can be used to measure the frictional properties of solids and unconfined granular materials. (2) In order to parse the effect of grain shape and strength on bulk granular flows, it is important to characterize these properties accurately. To do this we require an in-lab mechanical tester that can evaluate the hardness, elastic modulus, acoustic properties and fracture toughness of the specific granular material we are testing. A Nanovea PB1000 mechanical tester with Micro and Nano modules allows for such characterization through indentation and scratch tests on the same scale as indentation and scratch occurs within the granular shear flow. (3) A Retsch Technology Camsizer P4 will allow for detailed grain size and shape characterization while conserving the sample, so that we can evaluate grain size and shape before and after experimentation. This is required both to draw conclusions on the effect of grain shape on bulk rheology as well as to evaluate energy loss from grain breakage and fracture. Together, these three instruments will provide a complete system for building portable, predictive constitutive relationships between grain material properties, saturation, vibrational sensitivity, acoustic output, and bulk shear flow rheology. To the best of our knowledge, no laboratory has ever combined these techniques and thus the system presents a fundamentally new capability for study naturalistic granular flows.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010203
Entities
People
- Emily E. Brodsky
Organizations
- Army Contracting Command
- United States Army
- University of California, Santa Cruz