Date of Award

8-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Ahmad D. Vakil

Committee Members

Zhogren Yue, Basil N. Antar

Abstract

UTSI has developed a new low-cost jet-dry-spin method for the production of mesophase pitch-based carbon fibers. The objective of this preliminary study is to optimize the production of the UTSI carbon fiber composites and to better understand the surface texture between the fiber and matrix material. Several fabrication techniques were studied with varied preparation conditions to determine the effects on apparent density, electrical resistivity, tensile and flexural properties. Various polymeric resins and hardeners were used to demonstrate the versatility of the application of UTSI carbon fibers. During these investigations various analysis techniques including Scanning Electron Microscopy (SEM), x-ray diffraction, and optical microscope aided in the determination of the structural characteristics of the fiber and its composite.

It was found that vacuum bagging resin infusion is the optimal fabrication process due to its ability to minimize porosity and increase fiber volume/content. The use of extra slow hardener allowed excellent control over the wetting, degassing, and cure time. Increasing applied pressure during the fabrication of the composites increases the fiber content/volume leading to improvements in mechanical properties, apparent density and electrical conductivity. However, excessive pressure causes difficult diffusion of the resin and the crash of carbon fibers which decrease the above properties. A preliminary work also shows that low cost phenolic resin composites and converted C/C composites can be easily prepared using UTSI CF.

Fiber surface oxidative treatments with ozone and HNO3 solution were performed for comparison and optimization. Single-fiber fragmentation tests including single-fiber tensile/diameter testing revealed improvements in interfacial shear strength between oxidized carbon fiber (CF) and epoxy resin. Ozone treatment proved to be optimal, increasing flexure strength two-fold with respect to composites fabricated using as received CF.

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