Date of Award
Summer 2018
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
First Advisor
Borg, John P.
Second Advisor
Rice, James A.
Third Advisor
Fleischmann, Jonathan A.
Abstract
The dynamic response of granular earth materials such as sand has been of interest for many years. Multiple previous works have explored the shock response of sand in various grain shapes, sizes, and moisture contents, but the response during rapid combined loading has been relatively unexplored. The current study contributes to that lack of data by performing pressure-shear experiments on Oklahoma #1 silica sand, with quasi-smooth grains of 63 - 120 micron diameter and 99.8 wt.% Si02 composition. In these experiments, an oblique flyer plate impacts an equally inclined target, imparting a longitudinal (pressure) and transverse (shear) wave into a material of interest. The final loading states within the sand were inferred by measuring the normal and transverse components of particle velocity from the rear surface of the target using Photon Doppler Velocimetry (PDV). Tests were performed over a range of impact velocities to vary the magnitude of combined loading on the sand. Uncertainty in the calculated transverse particle velocity was explored for a variety of normal and angled PDV collimator setups to minimize the measurement uncertainty in shear stress. Combined loading in the experiments reached 0.25 - 1.00 GPa and 0.02 - 0.10 GPa of normal and shear stress, respectively. Yield surface models originally derived for lower strain rate loading of granular materials were shown to fit the experimental data in normal-shear stress space. The failure surface had a slope, or shearing resistance, of 0.130 and potential failure caps were presented. Scanning electron microscope images were taken of the recovered samples for 9 of 12 shots. Three-dimensional mesoscale simulations using an Eulerian hydrocode, CTH, were performed to better understand the experimental results and explore the boundaries of mesoscale formulations in Eulerian frameworks. Two different grain surface treatments were utilized, stiction and slide, to determine the influence of mixed cell treatments within CTH. Simulated normal stress - shear stress responses resulted in a shearing resistance of 0.172 and 0.176, for the sliding and stiction case, respectively, but failure caps were not observed for either mixed cell treatment.