Structurally efficient composite super ellipsoidal shells

Shells are thin-walled curved structures that react efficiently under applied load. They carry transverse loads by generating membrane stresses. However, inefficient bending stresses can also be generated. Bending stress suppression can result in more efficient use of ma terial and improvement of load carrying capacity of shells that is accompanied by significant weight reduction. These benefits mani fest themselves as a result of uniform load distribution through the thickness. Suppressing the bending moment and curvature changes simultaneously results in a bend-free design. This thesis considers a family of structures, i.e. super ellipsoids of revolution which are designed to have bend-free states under uniform internal pressure. Super ellipsoids of revolution have several advantages compared to conventional geometries. They have excellent packing efficiency as they can asymptotically approach a cubic shape. Moreover, they have small stress gradients because of their smooth variation of geometrical curvature. Super ellipsoids of revolution are inherently integrated which minimises the use of joints and assembly costs. Generalised set of governing equations for bend-free states in composite super ellip soids of revolution are developed and solved analytically. Bend-free designs are obtained by tailoring the stiffness using tow steering tech nology. Potential benefits of bend-free pressure vessels enabled by variable stiffness composite designs, make them possible candidates for the future pressure vessels. Failure performance of pressure ves sels is an important aspect for safety reasons. Therefore, the first-ply failure pressure is determined for bend-free variable angle tow ellip soidal pressure vessels and compared against conventional constant stiffness composite vessels using both Tsai-Wu and three-dimensional invariant-based failure criteria. Parametric studies evaluate the ef fect of various material properties on the difference in failure load predicted by these criteria that provides physical insight.