Structural Analysis of Carbon Fiber-Epoxy Composite Surfaces with Polar Stacking Sequences

Abstract

In this study, a new method of constructing graphite-epoxy carbon fiber structures is examined. The method studied consists of placing small strips of carbon fiber pre-preg into the desired mold such that fibers emanate outward from one or more poles. The goals of this study were to (1) construct a flat panel and predict the behavior of a simple structure with a polar stacking sequence, (2) determine if a hemispherical dome with polar lay-up will buckle during cooling using ANSYS ACP, (3) predict the strains and displacements within the dome due to pressurization using ANSYS ACP, (4) measure strains on the surface of the pressurized dome with polar lay-up using resistance strain gauges, fiber optic strain gauges, and digital image correlation, and (5) compare the measured and predicted strains. During this study, a methodology for constructing panels with polar stacking sequences was developed and a method for modeling the panels with polar stacking sequences was created using ANSYS ACP. Additionally, this method was applied to hemispherical domes using ANSYS ACP. By using an eigenvalue analysis to analyze the panels and dome, it was determined whether or not they structure would buckle. It was determined that both one and two pole panels would buckle due to cooling from the elevated cure temperature and the dome would not buckle. The strains measured by the resistance strain gauges and fiber optic gauge were compared to a standard classic lamination theory calculation and to the predictions made by the analyses performed in ANSYS ACP. The predicted and measured strains followed the same trends at all latitudes examined and were well captured by the ANSYS model. Additionally, the strain field captured by digital image correlation techniques agreed enveloped the predicted strain field from the ANSYS model. The digital image correlation techniques are subject to a significant amount of noise which made direct comparison of the scales difficult, however the gradients in the measured strain field were reflected in the ANSYS model.