Date of Award

6-15-2024

Document Type

Dissertation

Degree Name

Ph.D.

Organizational Unit

Daniel Felix Ritchie School of Engineering and Computer Science, Mechanical and Materials Engineering

First Advisor

Maciej Kumosa

Second Advisor

Joseph Hoffman

Third Advisor

Paul Predecki

Fourth Advisor

Yun Bo Yi

Fifth Advisor

Sandra Eaton

Keywords

Epoxy, Fracture toughness, Graphene oxide, Molecular dynamics, Nanocomposite, Polymer composites

Abstract

Thermosetting resins are used extensively worldwide in applications ranging from adhesives to structural components. However, these resins generally fail in a brittle fracture mode which is undesirable in most situations. Graphene (G) and its derivatives have been considered as additives to epoxy for material property enhancement and varied results have been reported in the literature. In this work, the effects of the oxidation of G to graphene oxide (GO) on polymer interactions and plate agglomeration were studied by classical molecular dynamics (MD). Results from those simulations concluded that agglomerates were likely present in all G-based nanocomposites. The effect of these agglomerates on epoxy was investigated by manufacturing G or GO-doped epoxy nanocomposites with no pre-exfoliation method and conducting mechanical property testing in tension, bending, and compression.

The response of GO/epoxy was different from that of neat and G-doped resin in all 3 tests, and under compression was dramatically different than under tension and bending. Under compression, the failure mode of the epoxy changed from brittle to slow tearing by adding 0.1 weight percent or greater of GO nanoplates. Computed tomography revealed the presence of previously unreported fissures in the GO samples, which were not seen in the neat or G-doped epoxy samples. These fissures appeared to inhibit crack propagation resulting in the slow, tearing failure mode in compression. Further MD simulations qualitatively supported agglomerations of GO in epoxy could nucleate void formation. Finally, the fracture toughness of these nanocomposites was estimated, showing that doping by agglomerated GO could increase the compressive fracture toughness of epoxy by approximately 1 to 2 orders of magnitude.

Although other means of altering the failure mechanism in epoxy exist, doping with GO resulted in a PMPC that showed no reduction in stiffness or coefficient of thermal expansion and should not suffer from thermal degradation as elastomer-doped resins are prone to. The compilation of studies presented in this dissertation lays the foundation for understanding a new energy-absorbing failure mechanism in thermosetting resins.

Copyright Date

6-2024

Copyright Statement / License for Reuse

All Rights Reserved
All Rights Reserved.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Matthew A. Reil

Provenance

Received from ProQuest

File Format

application/pdf

Language

English (eng)

Extent

201 pgs

File Size

117 MB

Download

Available for download on Thursday, February 13, 2025



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