Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Lacy Jr., Thomas E.

Committee Member

Gwaltney, Steven R.

Committee Member

Pittman Jr., Charles U.

Committee Member

Sescu, Adrian

Committee Member

Cheng, Yang

Other Advisors or Committee Members

Janus, Mark

Date of Degree

11-25-2020

Document Type

Dissertation - Open Access

Major

Aerospace Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Aerospace Engineering

Abstract

The non-reactive Dreiding and the reactive ReaxFF atomic potentials were applied within a family of atom molecular dynamics (MD) simulations to investigate and understand interfacial adhesion in graphene/vinyl ester composites. First, a liquid vinyl ester (VE) resin was equilibrated in the presence of graphene surfaces and then cured, resulting in a gradient in the monomer distribution as a function of distance from the surfaces. Then the chemically realistic relative reactivity volume (RRV) curing algorithm was applied that mimics the known radical addition regiochemistry and monomer reactivity ratios of the VE monomers during three-dimensional chain-growth polymerization. Surface adhesion between the cured VE resin and the graphene reinforcement surfaces was obtained at a series of VE resin “crosslink densities.” Both pristine and oxidized graphite sheets were employed separately in these simulations using a Dreiding potential. The pristine sheets serve as a surrogate for pure carbon fibers while oxidizing the outer graphene sheets serve as a model for oxidized carbon fibers. Hence, the effects of local monomer distribution and temperature on the interphase region formation and surface adhesion can be investigated. Surface adhesion was studied at various curing conversions and as a function of temperature. Uniaxial loading simulations were performed at different curing conversions for both models to predict the composites’ modulus of elasticity, Poisson’s ratio, and yield strength. The same analysis was performed for the neat cured matrix. The glass transition temperature (Tg) for the homogenized composite and neat VE matrix was determined at different degrees of curing. Subsequent MD simulations were performed to predict structural damage evolution and fracture in the neat VE matrix. The ReaxFF potential was used to quantify irreversible damage due to bond breakage in the neat VE matrix for different degrees of cure, stress states, temperatures, and strain rates. The predicted damage mechanisms in the bulk VE thermosetting polymer were directly compared to those for an amorphous polyethylene (PE) thermoplastic polymer.

URI

https://hdl.handle.net/11668/20836

Sponsorship

James Worth Bagley College of Engineering (BCoE), Advanced Composites Institute (ACI),

Comments

Molecular Dynamics (MD)||Interfacial shear strength (ISS)||Damage evolution||Glass transition temperature (Tg)||Mechanical properties||Free volume

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