Exact Modeling,Buckling Analysis And Collaborative Optimization Of Complex Composite Shells

Due to the complex service environment and demanding lightweight requirements of aerospace structures,designers have an urgent need for high-performance materials.Composite plate and shell structures have been widely used in aerospace engineering due to their high specific stiffness,specific strength,fatigue resistance,corrosion resistance and many other excellent material properties.In order to meet the requirements of aerodynamics and structural assembly,the complex geometry shells attract much more attention.Similarly,with the development of composite manufacturing technology,the manufacturing process of variable-stiffness composite structures is continuously improved and mass production is realized,and it has also been proved that the variable-stiffness structures achieve higher mechanical properties.Therefore,the variable-stiffness composite shells with complex geometry own a very broad application prospect.However,due to the dual complexity of fiber path and geometry,the traditional structural analysis and optimization design method is extremely time-consuming,which seriously slows down the research and development cycle of this kind of structure.Therefore,this paper focuses on the research of improving the mechanical properties of complex composite structures significantly and efficiently.In order to improve the analysis efficiency of the structure,Isogeometric anlaysis(IGA)as a burgeoning numerical calculation method is used to predict the critical buckling load considering that the main failure mode of this kind of structure is buckling.First of all,under the framework of IGA,using degenerated-solid shell element,the linear buckling theoretical formula of complex variable-stiffness structure is derived,and the linear buckling analysis based on IGA is realized using MATLAB.The research results show that the calculation efficiency of IGA is significantly higher than that of traditional finite element analysis,and the efficiency of IGA with third-order basis function is significantly higher than that with second-order basis function.And when the complexity of the structure increases,the efficient advantage of IGA is more obvious.Secondly,on the basis of the linear buckling analysis,the nonlinear buckling theoretical formula is further derived,and the adaptive load increment adjustment method is proposed to solve the nonlinear equilibrium equation quickly,which realizes the nonlinear buckling analysis based on IGA.The research results show that the analysis efficiency of IGA is greatly improved comparing the finite element analysis.The complexity of complex composite structures is mainly reflected in the geometry and the changeable fiber paths,and both are highly designable as well.In this paper,on the basis of linear buckling analysis based on IGA,in the aspect of fiber path optimization,a new fiber path characterization function is proposed,which expands the fiber path design space.And then,the analytical sensitivity of critical load to the fiber path control variables is derived to speed up the process of fiber path optimization.In the aspect of geometry shape optimization,two frameworks for shape optimization of complex shells are put forward and then compared,and it is found that the one based on LOFT function can provide representative control variables of shape and effectively reduces the number of design variables for complex shells.Finally,a novel collaborative optimization framework of fiber path and shell shape using IGA is established.By comparison of traditional methods,it is demonstrated that the proposed framework can greatly improve the efficiency of optimization and fully explore the buckling load of complex variable-stiffness shells.