Abstract

Composite conical and cylindrical shells are gaining more application in aerospace industry (e.g., helicopter tailboom, airplane fuselage) due to their high specific strength and stiffness properties coming from material (composite) and geometry advantages. Stability is always a concern for these types of structures under different loading conditions. One of the major loading scenarios is the bending load in which composite conical shells can buckle under bending. Although there have been extensive studies on the buckling of conical and cylindrical shells under axial load, buckling under bending receives less attention in the literature from theoretical and experimental points of view. In this study, the bucking behavior of composite conical shells has been studied experimentally and theoretically.
In the theoretical approach, a first order shear deformation shell theory has been proposed to study buckling and bending behavior of composite conical shells. A semi-analytical approach (Ritz method) has been applied to study buckling under axial load and buckling under bending of composite conical shells. An analytical solution (Levy type solution) has been applied to study the bending response of cross-ply conical shells under sinusoidal bending load. Also, a new formulation has been proposed to study bending, buckling and vibration of cross-ply cylindrical shells using an analytical solution (Levy type solution). A different displacement field from what was assumed in the literature has been proposed and consequently a new formulation has been obtained for the problem.
In the experimental approach, a composite tube-bending setup has been designed and developed to study bending, and buckling under bending load, behavior of composite shells. The setup has been designed to apply equal bending moments at the both ends of the structure, simulating pure bending test conditions. Experimental result has been obtained for buckling under pure bending of composite conical shells.
Regarding the manufacturing technique, Automated Fiber Placement (AFP) has attracted the aerospace industry due to its fast production rate, repeatability, and minimum material waste. Advanced thermoplastic composites obtain special attention in the aerospace industry as well, considering their superior properties (e.g., fracture toughness) and their capability to make aero-structures without requiring autoclave treatment with respect to thermoset ones. Considerable challenges remained unresolved regarding optimum process parameters for manufacturing of thermoplastic composites made by AFP and their quality. This thesis also addresses the effect of autoclave treatment on the stiffness quality of the thermoplastic composite cones made by AFP. The determination of optimum process parameters for AFP in the manufacturing of thermoplastic composite (AS4/PEEK) has been performed from both stiffness and strength point of view.