Masters Theses

Date of Award

12-1984

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

John F. Fellers

Committee Members

Walter Jones, J. S. Lin

Abstract

The characterization of voids in fiber reinforcements commonly used in high performance composites was studied using small x-ray scattering (SAXS) at the National Center for Small Angle Scattering Research. The void dimensions and void volume fraction was determined from the SAXS data for Kevlar® 49, for a pitch-based graphite fiber, and for two PAN-based graphite fibers. The accessibility of the voids in the fibers to a diffusing liquid was studied using SAXS with glycerin as the diffusing liquid.

Scanning electron microscope (SEM) micrographs were used to determine the ability of plasma etching to remove the skin from the core of Kevlar® 49 fibers. SAXS analysis was performed on the etched fibers to determine the effect of etching on the scattering pattern at the long and short geometry of the SAXS equipment. This led to the conclusion that the smallest voids are located in the core and the largest voids in the skin of the fiber.

Mechanical properties of epoxy resins cured with varying amine concentrations and Kevlar® 49 reinforced composites were determined using an Instron Mechanical Tester. The SAXS patterns of the epoxies and composites were obtained before and after fracture to determine if there was an increase in the scattering pattern due to the creation of voids in the material during the failure process. SEM micrographs of the fracture surface of the composites show fibers pulled out from the epoxy matrix, fiber splits along with skin damage and fiber skin-core separation.

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