Date of Award

2022

Document Type

Open 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 Odegard

Advisor 2

Susanta Ghosh

Committee Member 1

Ibrahim Miskioglu

Committee Member 2

Gowtham S.

Abstract

High-performance polymers are extensively used in the aerospace and aeronautics industries due to their low density, high specific strength, and high specific stiffness. These properties along with better infiltration with reinforcements [carbon nanotubes (CNTs), glass, etc.] capability make them an excellent candidate to fabricate Polymer Matrix Composites (PMCs) tailored for specific applications. The applications range from products used daily to deep space exploration. These materials are subjected to varying temperatures and pressures during fabrication and in service. Therefore, the evolution of their intrinsic properties needs to be studied and their ability to sustain extreme environmental conditions in outer space needs to be investigated. Utilizing experimental techniques for this purpose is time-consuming and expensive. Predictive computational tools like molecular dynamics (MD) can be used for such studies as they are quick and inexpensive relative to experiments. Furthermore, it reduces the overall time in designing and deploying the next generation of composite materials.

In this work, MD is implemented to model self-assembled stacks of flattened CNTs (flCNTs) and polyimide composites to investigate the interfacial properties at the interface between flCNT and polyimides. Fluorinated and non-fluorinated polyimides are compared based on interaction energy, friction force, and transverse strength. The reactive interface force field (IFF-R) is validated to predict thermo-mechanical properties of epoxies for varying degrees of cure. These nanoscale properties provide a set of inputs for microscale analysis to predict the evolution of residual stresses for the process modeling of composites. In order to use nanoscale mechanical properties as inputs, they need to be corrected for the strain-rate discrepancy associated with several orders of magnitude difference between experimental and simulated strain rates. A phenomenological approach to account for this strain-rate difference is developed based on experimental characterization data. Once the MD properties are corrected, they can be used in microscale analysis to accurately predict residual stresses.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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