Composite material is increasingly used in aerospace structures because of its improved specific properties and ability to be optimized for particular applications. This paper presents a technique for global layup optimization of symmetrically laminated composite plates with initial buckling constraints based on lamination parameters [1]. The method is computationally more efficient than previous solutions. The optimization problem is divided into two stages with continuous optimization followed by discrete optimization, in order to achieve the final optimum layup effectively using 0°, 90°, 45°and -45° plies. During the first stage, the optimal plate thickness and lamination parameters are obtained by using VICONOPT [2], a buckling program based on the exact strip method and Wittrick-Williams algorithm [3]. In the second stage, a Matlab program based on the branch and bound method is used to find the optimal stacking sequences to achieve the required lamination parameters obtained from stage 1. This program uses a layerwise approach [4] to enhance the optimization process. Three loops successively alter the ply orientations working inwards from the outer plies, which make a more important contribution to the flexural lamination parameters. This layerwise approach helps to obtain the optimum layup efficiently whilst achieving a reduction in computational cost. The software is used to design a number of symmetrically laminated composite plates under various loading conditions and subject to initial buckling constraints.

 References

 [1] Miki, M. and Sugiyama, Y. 1993. Optimum design of laminated composite plates using lamination parameters. AIAA Journal, 31 (4), pp. 921-922.

 [2] Kennedy, D. Fischer, M. and Featherston, C. A. 2007. Recent developments in exact strip analysis and optimum design of aerospace structures. Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science 211 (4), pp. 399-413.

 [3] Wittrick, W. H. and Williams, F. W. 1973. An algorithm for computing critical buckling loads of elastic structures. Journal of Mechanical Sciences 1 (4), pp. 497-518.

 [4] Kennedy, D. Park, B. and Unsworth, M. D. 2010. Towards global layup optimization of composite panels with initial buckling constraints. Proceedings of 8th ASMO UK/ISSMO Conference, London, pp. 221-231.