Civil Infrastructure Seminar: Nonlinear Elastic Properties of Rocks and Granular Media

Description

Abstract
Ultrasonic techniques can be used at the laboratory scale to characterize the elastic properties of rocks and granular media, which in turn helps us understand field observations made in various geophysical contexts (oil & gas, geothermal energy, earthquake physics). In particular, a subset of ultrasonic methods, referred to as nonlinear ultrasonic/acoustic techniques, is sensitive to the presence of micro-cracks and grain junctions. One of these nonlinear methods, called Dynamic Acousto-Elastic Testing (DAET) provides unprecedented details on the nonlinear elastic response of materials. The most striking feature is the appearance of a transient elastic softening, as soon as the medium is subjected to dynamic strains as low as 10−7. It is then followed by a log(t) relaxation back to the original elastic properties as soon as the dynamic loading is turned off. In this talk, I will first review some of the DAET results obtained in a wide range of materials from cracked metals to rocks and unconsolidated granular media. Next, I will present some of our most recent results where we investigate the effects of relative humidity and grain shape. Finally, we will discuss the microphysical origins of such phenomena and their geophysical implications.

Bio
Jacques Rivière is an assistant professor in the department of Engineering Science and Mechanics at Penn State. He earned a Ph.D. from the University of Pierre and Marie Curie in Paris, France (2012) and an M.S. in acoustics from the University of Le Mans, France (2008). He worked as a postdoctoral scholar at the Los Alamos National Laboratory (LANL) from 2012 to 2015 and in the Department of Geosciences at Penn State in 2015-2016. From 2016 to 2018, he was a Marie-Curie postdoctoral fellow at the Grenoble Alpes University in Grenoble, France. His research interests are in the areas of ultrasonics and geophysics, with applications to the nondestructive evaluation of materials, structural health monitoring, geothermal energy, CO2 sequestration, unconventional oil & gas and earthquake physics.

Hosted by Greg McLaskey, Associate Professor