Principal Investigator: William Griffith
Understanding of the behavior of geomaterials under different environmental and dynamic loading conditions is a critical need for mobility prediction and as input for projectile penetration prediction to destroy hardened and deeply buried targets. At the earth’s surface, the process of brittle fracture passes through a critical transition in rocks at high strain rates (101-103s-1). Within this strain-rate transition, the predominant mechanism for brittle fracture evolves rapidly from well-developed discrete, through-going fracture to fragmentation of the rock by distributed networks of short fractures. This transition is accompanied by increases in rock strength and energy required to induce rock failure. The increase in fracture surface area associated with the transition to fragmentation has been documented qualitatively using optical and scanning electron microscopy, however no effort has been made to quantitatively measure fracture surface area created during deformation experiments. I propose to conduct dynamic compression tests using a Split Hopkinson Pressure Bar (SHPB) on rocks across a range of strain rates, peak stress levels, and loading pulse durations to characterize the fracture networks in 3D using X-ray computed microtomography (CT). The results will yield estimates of the portion of the energy budget consumed in producing fracture surface area as well as physics-based models, constrained by experiments, to predict fracture surface area based on loading parameters such as strain rate and peak stress as well as lithology-specific characteristics such as mineralogy, grain size, and initial porosity.