Optimum Design Of Typical Laminated Composite Structures

How to reduce the aircraft structure weight is the goal that plane designers always pursuit. There are two main ways to reduce the weight of aircraft structures. One is to use large number of composite materials and advanced light alloys in aircraft structures, another is to use new technologies (for example, structure optimization design) to reduce the structure weight. Generally speaking, optimization design is to establish the model for a specific engineering problem, and adopt effective optimization method, through iterative approach to getting the strategy which both meets the constraint conditions and achieve the optimal objective function.The finite element model of a wing box structure was established in this paper, and the weight, the maximal displacement, the maximum strain and the first order of buckling modes of the initial design model are analyzed. On this basis, two optimization design models were established. The wing box structure weight was chose as the objective function, and the strength, stiffness and stability as well as relative manufacturing requirements were considered as constraints, and then the composite wing box structure was optimized using the OptiStruct software. The optimization process of the wing box structure includes three steps: free-size optimization, ply-bundle sizing optimization and ply stacking sequence optimization. The weight, the maximal displacement, the maximum strain and the first order of buckling modes were analyzed in each step. The optimization results show that the wing box structure weight is significantly reduced and the expected purpose is achieved with all constraints being met through three steps optimization.In this thesis, the optimization method on web of a C-section composite beam with a cutout and its edge reinforcement is presented. The whole beam web is divided into several areas, and then the thickness of each area was designed using size optimization to meet the allowable strain. In addition, the effects of the number of the areas that beam web was divided into on the optimized structure weight were analyzed. The results show that the more the number of the beam web is divided, the lighter the optimized beam web will be.