Date of Award:

2015

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Mechanical and Aerospace Engineering

Advisor/Chair:

Thomas Fronk

Abstract

Kenaf fibers have mechanical properties making them a good candidate to replace glass fibers in composites. This research investigates kenaf fiber-reinforced composites, examining the effect of cure time, density, matrix hardener ratio, surface treatment, and fiber length on the mechanical properties of the composite material such as natural frequency, damping loss factor, and tensile modulus. These are essential characteristics for many manufacturing parts and products, but are not well known for natural fiber-reinforced composite materials since interest in utilizing natural fibers for composites is in the infancy phase and determining properties is difficult. Natural fibers display properties similar to glass fibers, and present a more environmentally friendly option for manufacturing composite materials. By studying published research on the topic and experimenting with different methods, a consistent procedure for manufacturing composites was developed and several samples were created for testing these parameters. These samples were subjected to a vibrational test using an impact hammer and accelerometer. Through the half-power bandwidth method and other relationships, mechanical properties were extracted from the test to study the effect of each manufacturing process. Samples were found to exhibit repeatable mechanical properties after approximately 150 hours following removal from the oven. Increasing the pressure applied during the cure cycle results in higher densities, which increases loss factors and tensile moduli, and lowers natural frequencies. The matrix hardener ratio also affects these properties in a similar way. High hardener ratios result in a more brittle material that dampens less but generally has a higher stiffness. Models predict that a chemical surface treatment should decrease the loss factor due to a better fiber-matrix bond, resulting in less sliding and friction. However, testing showed the opposite result with treated fibers exhibiting higher amounts of damping. Fiber length was also tested, though the results showed a less prominent effect.

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