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Date of Award
Campus Access Dissertation
Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)
Administrative Home Department
Department of Mechanical Engineering-Engineering Mechanics
Gregory M. Odegard
Committee Member 1
Julia A. King
Committee Member 2
Committee Member 3
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.
Pisani, Will, "Molecular Dynamics Modeling of PEEK, Cyanate Esters, and Carbon Nanotubes for Aerospace Applications", Campus Access Dissertation, Michigan Technological University, 2019.