Layout Optimization Of Aircraft Wing Structure And Analysis Of Multistable Configurations Of Composite Laminates

The design of aerospace structures is required to meet the lightweight, high performance requirements. Conventional design methods rely mainly on the experience of engineers and design specifications. The lack of rational factor in structural design and the limitation on innovation make it difficult to deal with complex problems. Recently, due to the development of structural optimization theory and methods, the structural design is much more rational and reasonable. The reduction of structural weight and improvement of structural performance are achieved simultaneously. Therefore, structural optimization in engineering has wide application in many fields such as aerospace.In the design of modern aircraft wing structures, engineers need to find the optimum layout of structures and the optimum sizes and shapes of the components based on the engineering experience combined with structural optimization theory and methods. The traditional size optimization method can reduce the wing structural weight to a certain extent, while the structural layout optimization is to find the optimal load transfer path and radically reduce the structural weight. Therefore, it is of great significance to propose a reasonable and efficient method for layout optimization of wing structure. On the other hand, morphing research projects have received lots of attentions in the developed countries. Multi-stable structure is considered as one of the effective ways to achieve morphing structure. A multi-stable structure has two or several stable equilibrium configurations when unloaded. This kind of structure is much more efficient since it can remain stable under multiple configurations without additional energy to maintain the new configuration. The research on this kind of structure will bring more inspiration to the morphing aircraft design.On the above background, the layout optimization method for wing structural design considering the stability of composite skin is studied in this paper; Multi-stable configurations of composite laminate is analyzed and discussed from both analytical and numerical point of view. The main work in this paper is as follows:(1) The optimization design of wing structure considering the stability of composite skin. It is important to consider the stability of composite skin in the design of aircraft wing structures. Theoretically, it is very difficult to solve the stability of wing structures. Therefore, the simple and reliable empirical formula, which is a simplified method by analogizing with the theoretical analysis, is adopted in the engineering design.This paper focuses on multi-spar structure. The layout of the wing spars and the thickness of the skin have great effects on the stability of the composite skin, so a mathematical model on the layout optimization of wing structures is developed with the constraint of stability of composite skin in this paper. To solve this optimization problem, the stability of composite skin is solved based on the empirical formula, and the sensitivity formula is also established in this paper. Finally, a wing box structure is taken as an example, and the optimal results prove that the method presented in this paper is very effective in aircraft wing design.(2) Multi-stable configuration analysis of asymmetrically laminate under residual thermal stress. Residual stress on composite laminate will lead to thermal deformation. For some special layout, multi-stable configurations may be generated by residual stress. This paper focuses on this phenomenon and the theoretical methods are studied. In the terms of Energy Variational Principle, two different displacement functions are discussed in the analysis of orthotropic laminates, and multi-stable configurations of the structure is verified.(3) Numerical simulation on multi-stable configuration of asymmetrically laminates under residual thermal stress. Nonlinear finite element methods are employed to solve the structural large deformation problem by using ABAQUS software in this paper. In the terms of numerical analysis, the mechanical behaviors of different geometry and different ply of asymmetrical laminate under thermal stress are analyzed. Finally, the results are compared with that of Rayleigh-Ritz method. Multi-stable configurations of laminated composite structures are discussed in another point of view, which is basic research for the new configuration design in the future.