The Army Research Office has awarded a three-year grant of up to $357,330 to a University of Texas at Arlington geophysicist using new technology to better define the energy needed to fracture rock at the surface and below ground.
W. Ashley Griffith, an assistant professor of earth and environmental sciences, said the new research could give the Army information on how to address hardened and deeply buried targets, but the results could also easily be applied to improving civil engineering methods. The new grant also relates to Griffith's ongoing research using the latest technology to explore the science of earthquakes and a phenomenon in rocks known as "rate-strengthening."
Rate strengthening is when rocks get stronger when they are loaded faster, such as during an impact.
"Scientists know that rate strengthening when rocks break is related to the energy associated with microscopic crack growth. What we don't know much about is how this is related to rock texture and composition, so it is difficult to transform our theoretical knowledge into predictive capability," said Griffith. "This project takes advantage of UT Arlington's unique facilities and expertise in both geology and engineering to answer these questions."
Griffith will examine the relationship between "dynamic loading" - a term for the rapid input of energy from a fault or outside factor - and the progression of damage from the surface of a rock to a full fragmentation. These loading parameters, referred to the "strain rate" and "peak stress," differ for different materials.
Griffith joined the UT Arlington College of Science in 2012. Together with members of his laboratory, he conducts dynamic compression tests on a variety of rock materials using an instrument called a Split Hopkinson Pressure Bar. The device consists of two symmetrical metal bars on each side of a test object. Measured bursts from an air pressure gun on one end propel the bars into each other, straining the rock sample in-between. Strain gauges on each bar measure the energy load being exerted on the object.
In the Army Research Office research, Griffith will team with the Advanced Materials and Structures Lab (AMSL) in the Department of Mechanical & Aerospace Engineering at UT Arlington. They will use X-ray computed microtomography, also known as MicroCT, to create a 3D model of the fracture networks that his tests produce in a sample. The aim is to create physics based models that predict rock fracturing based on the strain applied and rock make-up, specifically examining characteristics such as mineralogy, grain size and initial porosity.
Asish Basu, professor and chairman of the UT Arlington Department of Earth and Environmental Sciences, said the grants Griffith has received "recognize Ashley's unique abilities to integrate theory, experiment and observations in his research in rock mechanics."
"He brings together multiple disciplines into play and, as a result, students and colleagues across different schools at UT Arlington, as well as the general discipline of rock mechanics, benefit from Ashley's creativity and scholarship," Basu said.
Griffith has previously received funding from the National Science Foundation to study the behavior of fractures in the earth's crust - a subject with implication for earthquake preparedness, mining and civil engineering and the tracking of subsurface fluid flow.
Griffith also recently received grant funding from the Southern California Earthquake Center. Those funds will help him study dynamic friction of materials from the San Andreas Fault Observatory, a rock core facility in Parkfield, Calif. He will use materials recovered from kilometers below the surface to test how they behave under stress levels and how their behavior relates to seismic slip during earthquake events.
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