Date of Award

8-9-2014

Document Type

Open Access Thesis

Department

Mechanical Engineering

First Advisor

Sarah Baxter

Abstract

Polymer nanocomposites can enable the innovative design of multi-functional materials. Metallic fillers in polymer matrices can exhibit improved electronic properties at low volume fractions while maintaining the low density, transparency, and easy processing of polymers. Surprisingly, mechanical properties also show enhancement at these uncharacteristically low volume fractions. Two mechanisms have been suggested as contributing to this enhancement. The first is the formation of a percolated microstructure; the second is the significant influence of the interface region between the matrix and filler. The majority of mathematical models describing this novel mechanical behavior are based on percolation models, which only consider microstructural connectivity. Changes in mechanical properties are likely to be affected by complex microstructures, beyond the simply connected, as well as by micromechanical mechanisms associated with these microstructures. These more complex microstructures and mechanisms may be challenging to identify and describe. In this work the underlying mechanical mechanisms are investigated using a probabilistic and statistical characterization of local strain fields. These continuous fields are more amenable to statistical characterization than the spatial ternary (matrix, particle and interface) fields that describe the microstructure. An apparent percolation threshold is identified based on statistical characterization of the elastic moduli, distributions of local strains and spatial autocorrelation of local strain fields. The statistics of strain fields associated with microstructures producing minimum and maximum moduli are also compared.

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