On The Comprehensive Optimization Design Of Aerospace Composite Thin-Walled Structures For Load-Carrying Efficiency

Due to high specific strength and stiffness,the composite thin-walled structures,including composite plates and shells and stiffened plates and shells,have been widely used as main bearing structures of aerospace equipment such as launch vehicles,missiles,and hyper-speed vehicles.In recent years,under the traction of space missions such as deep space exploration,there is a development trend of large-scale and heavy-duty for launch vehicles.The loading conditions of aerospace structures have become more and more severe and extreme.Moreover,with the development of the aerospace industry,design requirements of low cost and lightweight are further put forward for aerospace structure.In order to solve the contradiction between lightweight and large-scale aerospace structures,it is urgent to improve the loadbearing efficiency of aerospace equipment structures in China.In response to the above requirements,the aerospace composite thin-walled structures are taken as the research object in this paper.The paper focuses on the research of low-cost design,variable stiffness innovative configuration design,and the lightweight design for shells with high imperfection sensitivity.First,to reduce the material cost and the design cost of structures,a multi-scale variable concurrent optimization method and a discrete material diverse design method are proposed to realize the low-cost design of composite thin-walled structures.Then,based on different optimization strategies,optimization frameworks for innovation variable stiffness are proposed respectively for fiber-reinforced and stiffened plate and shell structures.Subsequently,the research on imperfection sensitivity analysis is carried out for aerospace thin-walled cylinders,and different imperfection sensitivity analysis methods are comprehensively compared.Furthermore,the incomplete reduced stiffness method is proposed to realize the accelerated imperfection sensitivity analysis for imperfect cylindrical shells.Finally,for the variable stiffness composite cylinders and the stiffened cylinders,the optimization design of aerospace cylindrical shell oriented to imperfection tolerance is performed,which improves the bearing capacity on the premise of ensuring the lightweight of the cylindrical shell structures.Besides,a fast optimization design framework for axially compressed stiffened cylindrical shells oriented to imperfection tolerance based on the incomplete reduced stiffness method is established,which improves the optimization efficiency of the cylindrical shells considering the imperfection sensitivity.The main works of this dissertation are given as follows:(1)Aiming at the low-cost design problem of the aerospace plate and shell structures,taking the reduction of the material cost and design cost of plates and shells,a multi-scale variable concurrent optimization method and a discrete material diverse design method are proposed.First,a candidate material set considering design variables on different levels is established.The multi-scale variable concurrent optimization of hybrid fiber composite panels and shells under low material cost constraints is realized through the Discrete Material Optimization.Moreover,diverse designs for low material cost hybrid fiber composite plate and shell structures are developed.Multiple design solutions with different potential properties are provided to reduce the probability of design changes and engineering rework and improve the design efficiency of the product,realize the purpose of shortening the design cycle and reducing the design cost.(2)In order to obtain an innovative plate and shell structure design with lightweight and high load-bearing characteristics,research on the variable stiffness design methods for the aerospace plate and shell components with different configurations are carried out,respectively.The discrete material topology optimization method and curve-path-based shape optimization method are used to perform the variable stiffness designs for fiber-reinforced composite plate and she]]structure,respectively.A variable stiffness optimization method that integrates topology,shape and size optimization is developed for the stiffened plate and shell.All of the above methods can effectively improve the force transmission path of the plate and shell structure and obtain the innovative variable stiffness structural design of the aerospace plate and shell,whose mechanical properties are greatly improved.(3)For the problem of the imperfection sensitivity of thin-walled cylindrical shell structures in aerospace,the main imperfection sensitivity analysis methods in recent years have been reviewed.The axial compression buckling test data of cylindrical shells in the public literature are collected.Moreover,the KDF design guideline formula of the axial-compressed cylindrical shell is updated based on the experiment data in recent years.Subsequently,based on the test data,a comprehensive comparison of different imperfection sensitivity analysis methods is carried out.Furthermore,aiming at the low efficiency of imperfection sensitivity methods based on the nonlinear post-buckling analysis,such as the worst multiple perturbation load approach(WMPLA),an accelerated analysis method for the bearing capacity of imperfect cylindrical shell structures with imperfection—incomplete reduced stiffness method(iRSM)is developed.While satisfying the requirements of analysis accuracy,the computational cost of bearing capacity analysis for imperfect cylindrical shell structure is significantly reduced.(4)In order to improve the load-bearing capacity of the thin-walled aerospace cylindrical shell structures while ensuring the level of lightweight,thereby increasing its safety margin and obtaining a high design load and high-robustness aerospace cylindrical shell structure design,the optimization design of the aerospace cylindrical shell structure oriented to imperfection tolerance is performed.The coupling relationship between structural buckling load and imperfection sensitivity is fully considered in the optimization process of the variable stiffness composite cylindrical shell and the stiffened cylindrical shell structure.So that,the improvement of design load and robustness is realized by simultaneously improving the buckling load and anti-imperfection ability of the cylindrical shell structure.Furthermore,aiming at the problem of low efficiency in the optimization design of imperfect cylindrical shell structure,based on the incomplete reduction stiffness method,an imperfection toleranceoriented axial compression stiffened cylindrical shell rapid optimization design framework is established.The optimization efficiency of the cylindrical shell that considers the imperfection sensitivity is improved.