(Dr. Steven Johnson, advisor)

"Characterization of the Debonding of Graphite/Epoxy-Nomex Honeycomb Sandwich Structure"

Abstract

A method for measuring and analyzing fracture toughness and fatigue debond growth behavior of a composite sandwich structure was proposed. The structure studied was composed of a Nomex honeycomb core with thin graphite/epoxy facesheets. This and similar structures are highly utilized on commercial aircraft. It is the eventual goal to incorporate fracture properties of the materials into maintenance regulations. Critical strain energy release rates, a measure of fracture toughness, and da/dN vs. DG fatigue curves were developed at cold (-65^oF), hot (170^oF), and room (72^oF) temperatures. Specimens were subjected to three environments of aging in addition to the as-received condition. Underwater soaked, thermally cycled, and isothermally conditioned specimens were tested. The test geometry was adapted from the popular Double Cantilever Beam configuration, with several necessary modifications due to the uniqueness of the tests performed. Data was reduced using a compliance calibration technique, as damage propagation proved difficult to accurately measure by visual observations. The effects of the test parameters as well as the experimental and analytical techniques were studied.