Nonlinear elastic properties of granular media: The effects of stress, relative humidity, and grain shape

Abstract

The long-term goal of this work is to elucidate the microphysical mechanisms responsible for the nonlinear elastic properties of rocks and granular media. Nonlinear elasticity in such media arises from the weak junctions between grains, however the precise microphysical mechanisms at play remain to be determined. In our previous work, we found that (1) in rocks, the nonlinear elastic parameters cluster in two groups, suggesting that there are two main physical mechanisms, (2) despite their differences in grain shape, the elastic nonlinearity of spherical glass beads and angular fine sand is of the same magnitude, however (3) the elastic nonlinearity increases with relative humidity (RH) for glass beads, while it remains quite constant for fine sand. To further refine these observations and reduce scatter, here, we present preliminary results using a new setup that allows us to quickly vary the relative humidity of a single sample, rather than comparing different samples at different RH. We monitor the nonlinear elastic response of our samples using Dynamic Acousto-Elastic Testing and systematically vary the stress and RH. Interpretation of these new results in light of our previous work are discussed.