Optimization of anisotropic laminated composite plates incorporating non-conventional ply orientations

In laminated composite design, ply orientations are generally restricted to 0, 90, ± 45 degrees. This is often due to manufacturing limitations. However, studies have shown that an expanded set of ply orientations may lead to more efficient structures. Using a larger set of ply orientations, including non-standard fibre orientations, imparts greater elastic tailoring capabilities which may bring associated gains in efficiency or indeed functionality. In particular it has been shown that 60 degree plies are optimum for shear in buckling for long anisotropic composite laminated plates. In this paper a two-level optimization approach, using an expanded design envelope of 0, 90, ± 45, ± 30 ± 60 degree plies, is presented. At the first level, gradient based methods are used to minimize the mass of a simply supported composite plate under different loading conditions. At the second level, a particle swarm optimization algorithm is used to determine laminate stacking sequences. Using an expanded design envelope of ply orientations, it is shown that mass savings of up to 7.4% can be achieved for an unbalanced symmetric laminate. Specifically, mass savings are made for geometries where the plate has a large aspect radio and is predominantly shear loaded. Additionally, it is shown that the particle swarm optimization performs well and achieves feasible designs which satisfy the design constraints.