Initial sizing optimisation of anisotropic composite panels with T-shaped stiffeners

This paper provides an approach to perform initial sizing optimisation of anisotropic composite panels with T-shaped stiffeners. The method divides the optimisation problem into two steps. At the first step, composite optimisation is performed using mathematical programming, where the skin and the stiffeners are modelled using lamination parameters accounting for their anisotropy. Skin and stiffener laminates are assumed to be symmetric, or mid-plane symmetric laminates with 0°, 90°, 45°, or −45° ply angles. The stiffened panel is subjected to a combined loading under strength, buckling and practical design constraints. Buckling constraints are computed using closed form solutions and an energy method (Rayleigh-Ritz). Conservatism is partially removed in the buckling analysis by considering the skin-stiffener flange interaction and decreasing the effective width of the skin. Furthermore, the manufacture of the stiffener is embedded within the design variables. At the second step, the actual skin and stiffener lay-ups are obtained using genetic algorithms, accounting for manufacturability and design practices. This two step approach permits the separation of the structural analysis (strength, buckling, etc.), which is performed at the first step, from the laminate stacking sequence combinatorial problem, which is dealt efficiently with genetic algorithms at the second step.