Optimization Design Of The Thin-walled Components And Frame Structures With Crashworthiness Criterion

Vehicle passive safety is one of the key problems for the automobile industry. How to improve the crashworthiness of vehicles has been the key issue of the automotive safety. The thin-walled metallic components---the most conventional and effective energy-absorbed device,have been widely used in the automotive design and manufacture. The energy-absorbed characteristics of the components not only have close relation with their characteristics but also are significantly affected by other parameters such as the cross-sectional shape and geometric size of the components, and the type of trigger as well as the way of loading. Therefore, the crashworthiness research on the relationship between thin-walled metallic components and the above parameters that affect its energy-absorbed characteristics have an important guidance on the design of the automotive crash safety. And there are notable engineering significance and academic value to seek one optimal design method. Based on the existing research achievements and by use of the explicit finite element technique, response surface method and evolutionary structure optimization method, the thin-walled components and frame structures under impact load have been investigated and optimized in this thesis.Base on the existing research achievements on the crashworthiness optimization, the recent developments of theories and simulations for thin-walled structures and frame structures are briefly summarized. In order to overcome difficulties in numerical optimization analysis such as instability, uncertainty and high nonlinearity, based on the surrogate model theory and the related optimization method as well as the crash software the optimization method and process for automotive crash safety are presented. Based on the above process, crashworthiness optimization for a thin-walled tube with uniform square section is taken as an example to test the optimization process, and the results show the feasibility and validity of this method.In terms of the crash energy absorption and weight efficiency, a multi-cell cross-section tube and an adhesive flange cross-section tube are designed and optimized respectively. The optimization process with the target of maximizing the Specific Energy Absorption (SEA) has been successfully carried out, and the new structures show dramatic improvements over the conventional square tube. Then, the tapered thin-walled square tube is optimized. The geometric parameters of the tapered tube are chosen as design variables. The maximization of the energy absorbed by the structure, the maximization of the Specific Energy Absorption (SEA), and the minimization of the initial force peak are considered as the multi-objective functions. The objective functions are constructed based on the response surface method. The multi-objective optimization for the tapered thin-walled square tube is presented by using the ideal point method and introducing weighted coefficients characterizing the priority of each objective function in the design.According to the theories of frame structure topological optimization under static loading, the evolutionary structure optimization method is firstly introduced into the frame structure topological optimization under impact loading. In this method, the ratio of elemental strain energy to the highest strain energy is adopted as a factor to determine the relative efficiency of material usage, and the ratio of total stain energy to total structural weight is established in order to decide whether an optimum has been reached. The feasibility and efficiency of the evolutionary structure optimization have been tested by an example of 2D-frame structure crash optimization.The results of this thesis indicate: the optimization method and the process based on surrogate model are quite effective in the automotive crash safety. If choosing the appropriate surrogate model and optimization methodology according to the above method and process, the puzzle of the automotive passive safety optimization can be solved quickly, economically and exactly, which has a significant use in the reference to the automotive crash safety design optimization.