Inter-particle cementation, particle porosity, and moisture effects on wave propagation in granular materials
An experimental investigation was conducted to study the effects of inter-particle cementation, particle porosity, and pore fluid on dynamic wave propagation in particulate materials. The experimental work was augmented with theoretical and computational models as necessary to explain the observed behaviors and aid in data analysis. Further, fiber optic sensors were investigated for their application to contact mechanics problems.^ The work has shown that inter-particle cementation dramatically affects the nature of the stress field in simulated granular media. Cements which are stiff when compared to the disk material produce the highest stresses in the region adjacent to the edge of the cement, while soft cements produce the highest stresses adjacent to the center of the cement region. The relative cement stiffness also affects the group wave velocity in particle chains. Extremely stiff cements produce high group wave velocities and very soft cements almost block wave propagation altogether.^ Micro-structural particle porosity results showed that the velocity decreases with increasing porosity for all specimen geometries. However, characteristic group wavelength behavior differed widely between the three specimen geometries. In general, the experiments showed that the degree of porosity alone is not the dominant factor in determining the effects on dynamic waves.^ The effect of inter-particle moisture was investigated with fully and partially saturated assemblies of model particles. Results indicate that there is no change in the stress field within the particles due to the presence of the fluid. Analysis showed that for fully saturated assemblies, like the dry contact, there was no significant dispersion. However, there was a dramatic difference in attenuation behavior between the fully and partially saturated assemblies when compared to their dry counterpart.^ The experimental work with fiber optic sensors shows that they may be used for contact mechanics problems with an acceptable degree of accuracy. The experiments and the desired data should govern the specific sensor to be chosen. A sensor developed in the laboratory shows great promise for use in large displacement applications as well as low amplitude oscillations. ^
Frank Joseph Sienkiewicz,
"Inter-particle cementation, particle porosity, and moisture effects on wave propagation in granular materials"
Dissertations and Master's Theses (Campus Access).