Date of Award

Winter 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Johrendt, Jennifer L.

Second Advisor

Frise, Peter R.

Keywords

Applied sciences, Fiber-reinforced polymers, Buckling, Laminated composites, Pultrusion, Stringers, Torsion

Rights

CC BY-NC-ND 4.0

Abstract

Fibre reinforced polymer (FRP) materials offer many advantages over conventional metallic structural materials due to their high specific strength and stiffness, long fatigue life, and resistance to environmental corrosion. However, these materials present some unique engineering challenges due to their anisotropy and heterogeneity. The connection of these composite parts to adjacent components often results in complex and counter-intuitive states of stress that can be quite difficult to model. Furthermore, since these materials are, in a sense, synthesized during the fabrication of the final part, the mechanical properties that can be expected from FRP structures are largely dependent upon highly skilled workmanship. Pultrusion is a manufacturing technique that is intended for the mass-production of long FRP parts having continuous cross-sectional geometry. Although it has not yet been optimized for the aerospace industry, with some qualification research, pultrusion may prove to offer many benefits over conventional methods of manufacturing composite aircraft parts. The present dissertation investigates the possibility of co-pultruding FRP parts with embedded non-FRP materials (such as metallic materials), which could serve as integral hard points to facilitate serviceable mechanical connections to adjacent parts. It is shown that these hybrid co-pultruded members offer substantial light-weighting benefits over conventional metallic components, while retaining the ability to employ serviceable mechanical fasteners. Simple unidimensional beam models are of great value when validating the results of complex finite element analyses of aircraft wing-stringers, or other similar structural members. It is demonstrated in the present dissertation that classical unidimensional beam-type analytical models often yield unconservative predictions (over-predictions) of stiffness and elastic stability when used for the analyses of FRP beams and columns. In fact, specific examples are included in which classical methods are shown to over-predict torsional stiffness by 111.3%, over-predict warping stiffness by 40.3%, and over-predict critical column buckling loads by 103.63%. As such, this dissertation presents additional analytical procedures that enhance the fidelity of these classical analytical methods such that they can be utilized to accurately assess the stiffness and elastic stability of FRP beams and columns, including the hybrid composite co-pultruded members that are proposed in this dissertation.

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