Buckling Analysis and Optimization of Stiffened Composite Flat and Curved Panels

This work presents the buckling optimization of composite stiffened panels loaded in compression and shear. The procedure relies on the coupled use of a semi-analytical formulation for the structural analysis together with an optimization based on genetic algorithms. The semi-analytical formulation allows the assessment of the local buckling behavior of panels with blade, J, T, and hat-stiffener cross sections. The out-of-plane buckling deflections of the skin and of the stiffener are represented by trigonometric shape functions, and the governing equations are derived applying the principle of the minimum potential energy and the method of Ritz. The formulation is used to obtain optimal configurations in terms of skin and stiffener lay-ups, stiffener cross sections, and geometry. Constraints can be imposed on the structural response in terms of buckling load and prebuckling stiffness as well as on technological requirements. The optimal design is presented for the buckling load maximization of a flat hat-stiffened panel loaded in compression and shear and for the minimum weight under buckling constraints of a curved panel with open-section stringers loaded in compression. The results obtained from the semi-analytical formulation are then compared with finite element analyses.