## Dissertations - ALL

June 2017

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Physics

Mary E. Manning

Claudia Miller

#### Keywords

disorder, jammed, vibration

#### Subject Categories

Physical Sciences and Mathematics

#### Abstract

In this thesis, I will investigate the properties of disordered materials under strain. Disordered materials encompass a large variety of materials, including glasses, polymers, granular matter, dense colloids, and gels. There is currently no constitutive equation based on microscopic observables that describes these materials. Given the prevalence and usefulness of these materials, we derive tools to aid our understanding of them.

We develop a new method to isolate localized defects from extended vibrational modes in disordered solids. This method augments particle interactions with an artificial potential that acts as a high-pass filter: it preserves small-scale structures while pushing extended vibrational modes to higher frequencies. The low-frequency modes that remain are bare" defects; they are exponentially localized without the quadrupolar tails associated with elastic interactions. We demonstrate that these localized excitations are excellent predictors of plastic rearrangements in the solid. We characterize several of the properties of these defects that appear in mesoscopic theories of plasticity, including their distribution of energy barriers, number density, and size, which is a first step in testing and revising continuum models for plasticity in disordered solids.

We additionally study the properties of rearrangement types in 2D disordered packings of particles with a harmonic potential at a range of packing fractions above jamming. We develop a generalizable procedure that classifies events by stress drop, energy drop, and reversibility under two protocols. Somewhat surprisingly, we find a large population of contact change events that have no associated stress drop. Reversible events become more common at high pressures above a packing fraction of $\phi=0.865$, at which point line reversible events are more common than loop reversible events. At low pressures, irreversible events are associated with spatially extended events, while at high pressures reversible events are much more spatially localized.

Open Access

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