Optimum stacking sequence design of symmetric hybrid laminates undergoing free vibrations

The design of hybrid symmetric laminated plates consisting of high-stiffness surface and lowstiffness core layers is presented. The maximisation of the fundamental frequency and frequency separation is performed over a discrete set of available ply angles. Minimum cost design using a hybrid construction is determined subject to a constraint on the fundamental frequencies or frequency separation. Boolean variables are introduced to specify stacking sequences and to obtain an expression for the frequency which is linear in terms of the design variables. Solution of the linear optimisation problem yields an optimal stacking sequence for the specified objective function. The effect of hybridisation is investigated for various parameters of the laminate such as the aspect ratio and the number of plies. Results are given for hybrid graphite-epoxy/glass-epoxy laminates