An analytical model for interactive design of cylindrical composite ducts with upright bolted flanges

A novel closed-form analytical model is described and applied to predict the stiffness and stress distributions around the circumference of cylindrical composite ducts with upright bolted flanges. Each ply in the laminated flange or shell section of such a duct is laid-up of circular segments, or “gores”, which are stamped out of a prepreg unidirectional tape or woven fabric, through a “cookie-cutter” type operation. The gores are then butted in the circumferential direction, constrained by tooling in the radial direction, to complete the circular contour of each ply. The individual plies are stacked over each other in an interleaved sequence, so that every transition region from one gore to another is fully covered by the continuous gores of the adjacent plies. Typical results generated by this model are illustrated here for a Carbon T-300/Bismaleimide material system. The results indicate that the size of the gore pieces can be increased in order to reduce manufacturing costs, without significant stiffness or weight penalties, if the interleaving pattern is properly tailored to specific loading scenarios.