Date of Award

2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Physics & Astronomy

First Advisor

Douglas J. Durian

Abstract

A microscopic understanding of how amorphous materials deform in response to an imposed disturbance is lacking. In this thesis, the connection between local structure and the observed dynamics is explored experimentally in a disordered granular pillar subjected to a quasi-static deformation. The pillar is composed of a single layer of grains, allowing for easy visualization of all particles throughout the deformation. The addition of a liquid into the system causes capillary bridges form between the grains, making the grains cohesive. The two-dimensionality of the system ensures that the liquid is distributed uniformly throughout the packing, making the cohesive forces between the grains known everywhere. We perform separate experiments to measure these capillarity-induced forces, and we find these measurements to be in excellent agreement with our theoretical model and numerical calculations. In the main experiments presented in this thesis, we explore the quasi-static deformation of granular pillar subjected to uniaxial compression. We find a statistical correlation between the local dynamics, characterized by the deviatoric strain rate, and the local structure, characterized by a new measure, introduced here, akin to a relative free area. This correlation is stronger in the presence of cohesion and indicates that regions that are more (less) well packed relative to their surroundings experience lower (higher) strain rates than their surroundings. The deviatoric strain rate also highlights shear bands within the deforming pillar. These shear bands are transient, moving around as the compression occurs. We have developed a way to identify these extended bands, and we compare the structure within these bands to the structure outside. Preliminary results suggest that these shear bands coincide with paths through the material that tend to have more underpacked regions than other parallel in the vicinity of the shear band.

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