Date of Award

2019

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Gregory M. Odegard

Committee Member 1

Julia A. King

Committee Member 2

Ibrahim Miskioglu

Committee Member 3

Gowtham Shankara

Abstract

For transportation of humanity to Mars and beyond, our space vehicles will require a pressurized cabin, and large stores of fuel, food, and water, all of which add tremendous weight. This dissertation is concerned with the molecular dynamics (MD) modeling of three polymers (PEEK, a fluorinated cyanate ester, and a non-fluorinated cyanate ester) which are candidates for the matrix material of next-generation, ultra-strong, lightweight structural materials suitable for deep-space missions.

The relationship between the multiscale, semi-crystalline nature of PEEK and its mechanical properties is not well-understood. Reactive MD modeling was used to predict the mechanical response of the amorphous and crystalline phases of PEEK. Employing the MD simulation results as input, the hierarchical microstructure of PEEK, which combines these two phases, was modeled using NASA's micromechanics MSGMC (Multi-Scale Generalized Method of Cells) code. The predicted bulk mechanical properties of semi-crystalline PEEK agree well with the scientific literature data, thus validating the multiscale modeling approach.

One avenue to creating ultra-strong, lightweight composites is combining aerospace-grade polymers with CNTs. Nanocomposites of polymer and CNTs at a variety of polymer mass fractions were modeled with MD using the Polymer Consistent Force Field - Interface Force Field (PCFF-IFF). The compatibility between each polymer and CNTs was assessed through three different metrics: adhesion, friction, and opening mode separation. The criteria within each metric are: for adhesion, interaction energy between polymer and CNT; for friction, friction force between polymer and CNT when one CNT is pulled at a constant velocity; and for opening mode separation, stiffness, strength, and toughness. Based on the results of these three metrics, the fluorinated cyanate ester is recommended as the matrix of a polymer/CNT composite.

Available for download on Thursday, October 01, 2020

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