Granular packs (soils, sedimentary rocks, industrial powders, crowded bacteria, pills, foodstuffs) typically exhibit localized deformations during loading: severe relative displacements amongst grains occur within localization zones, whereas minimal deformations are suffered by the rest of the material. Localization varies with type of loading (e.g., shear vs. compaction), packing characteristics (e.g., porosity), and grain characteristics (e.g., sizes, shape, roughness, internal porosity). This project centers on localized compaction, i.e., porosity loss in the localization zone, and focuses specifically on elucidating a recently discovered phenomenon: the periodic propagation of localized compaction in granular packs composed of porous grains. Laboratory experiments that involve load-deformation and granular breakage measurements, acoustic emission and wave velocity monitoring, and video capture for digital image correlation analyses are implemented to understand why and how such phenomenon takes place. This understanding is attained by characterization of the propagation process (i.e., speed, spatial extent, periodicity) and identification of the range of conditions required for its manifestation, placing emphasis on the role that material properties (e.g., grain crushability), loading conditions (e.g., imposed deformation rate), and boundary conditions (e.g., near vs. far) play on the characteristics of the deformation response.
This work will lead to an increased understanding of localization mechanics and nonlocal effects in granular materials. In turn, this understanding shall serve in furthering the development of characterization and prediction tools for processes wherein localization takes place, including soil and rock engineering (e.g., fault gauging, slope instability, in-site soil testing), and geo-mechanics (e.g., hydrocarbon production and reservoir damage) processes, natural and industrial granular flows, snow avalanches, and deformation of non-granular porous solids, such as engineered cellular foams and composites. This project supports undergraduate and graduate research students, furthers collaboration between a Hispanic-serving institution (San Diego State University) and an international research university (University of Sydney), and contributes to the Nation?s commitment to entice middle- and high school students towards the study of science and engineering, through the development of research-related didactic tools coupled with teacher-training implemented within the nationwide program Project-Lead-the-Way.
