An experimental study of granular packing structure changes under load

A novel experimental method has been developed to characterize the packing structures of granular materials. This method can be used to identify microstructural parameters for granular materials required in micromechanical modeling. Important parameters include volume fractions, particle arrangements, and contact geometries, as well as packing structure changes under applied loads. In this effort, these microstructural parameters have been quantified directly from actual material samples, not from hypothetical or numerically generated structures. The developed method utilizes a high resolution X-ray computerized tomography (CT) machine to non-intrusively acquire cross sectional images of material samples. A special loading device is designed to fit on the CT machine’s sample stage to apply loads during CT scanning. Numerical algorithms have been developed to analyze these CT images and obtain three-dimensional (3D) packing structures of granular materials. Microstructural parameters are then extracted from the reconstructed packing structures at each loading step. Correlations between the macroscopic behavior (stress-strain relations) and corresponding microscopic packing structure changes are studied.