Date of Award

May 2014

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Rani F. Elhajjar

Committee Members

Konstantin Sobolev, Craig M. Clemons

Keywords

Dma Viscoelastic Properties, Mechanical Properties, Nanocellulose, Natural Fibers, Polymer Matrix Composites, Triaxially Braided

Abstract

Fiber-reinforced composite materials are increasingly used for structural and engineering purposes. In particular, composites reinforced with natural fiber systems are becoming more and more popular due to their biodegradability and abundance; added to that other properties such as transparency, dimensional stability and good mechanical behavior. However, major issues remain to properly understand their behavior and enable their widespread use.

In this thesis, the mechanical behavior of cellulose fiber/epoxy composites is investigated. The natural fiber systems studied fall into three categories: unidirectional regenerated cellulose fibers, triaxially braided quasi-isotropic regenerated cellulose fibers and micro-fibrillated cellulose in the form of nanocellulose scaffolds. Different methods of fabrication including wet layup, resin infusion, hot pressing and combinations of the three processes were investigated. Mechanical testing of tension coupons or three-point bending was performed to assess the mechanical behavior. When permitted, mechanical testing was accompanied by other validation techniques to help understand the mechanical behavior including digital image correlation (DIC) and acoustic emission. The effect of temperature and loading frequency on the mechanical behavior was also investigated by performing short beam testing using Dynamic Mechanical Analysis (DMA). Environmental effects, mainly the effect of moisture on the behavior of the fibers and the composites was also investigated. Additionally, the effect of the level of cure of the resin was found to have a detrimental effect on the mechanical behavior of the composites and was studied using DMA and Digital Scanning Calorimetry (DSC). Finally, the experimental results were extended and validated using numerical solutions and finite element simulations. Results show that thermal and mechanical properties are highly sensitive to the different factors being investigated; mainly humidity, temperature, manufacturing procedure and parameters, fiber content, as well as the level of curing of the epoxy.

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