Dynamic Contact Mechanics of Geologic Materials: Experiments, Modeling and Applications

Abstract

Although stress wave propagation in granular geologic materials is generally recognized to depend critically on the physical characteristics of the medium, there is a lack of understanding of the physical basis of this process. This knowledge gap inhibits the development of mechanistic models of wave propagation in granular materials and of soil-sensor interaction. To address this important issue, we are currently engaged in an effort to quantify and model the dynamic contact mechanics of granular materials using a combination of micro-scale experimentation, numerical modeling and field validation.

We have developed a dynamic contact experimental system that operates at sub-kHz frequencies. This laboratory based system employs piezoelectric crystals to monitor the force transmitted though contacts in a linear array of grains of geologic materials. The deformation over single or multiple contacts is measured, allowing the constitutive behavior of the contacts to be quantified. The paper describes this system in a configuration for normal loading, and presents initial results for a large-grained quartz sand. Our approach to developing detailed contact laws (that account for both elastic and inelastic deformation) is described.

The implementation of material-specific contact laws in a discrete element model is also described with a focus on small normal displacements. The DEM simulates wave propagation as a function of measurable grain-scale properties and includes the simulation of polyellipsoidal and polyhedral particle shapes and Hertzian and non-Hertzian laws for contact stiffness and frictional loss. In addition, the paper describes a number of research interests that are supported by this work.