Optimization Design Of The Thin-walled Components With Crashworthiness Criterion

Safety, environmental protection and energy conservation are the three principal problems of the 21st century. Meanwhile, how to improve the crashworthiness of vehicles has been an assignable issue during the analysis of passive safety of the automotive. Researches of automotive crashworthiness are mainly concentrated on the energy absorption performance of components of the car body during impact events. A good energy absorption device can transform as much kinetic energy as possible into the structural strain energy in an irreversible pattern during crashing. As the most conventional and effective buffer energy-absorbing devices, the metallic thin-walled components have been widely used in the automotive design and manufacture. Expect for the material characteristics of the components, the metallic thin-walled tubes also have close relations with some dimensional parameters such as cross-sectional shape, thickness and so on. Therefore, crashworthiness researches and optimization designs on metallic thin-walled tubes have been a very important aspect of the car body optimization with crashworthiness criterion. In the recent years, there have been many literatures on crashworthiness optimization of metallic thin-walled components. On the ground of others'researches and based on explicit finite element technique and response surface method, some thin-walled components with the special cross-sections have been optimized with the crashworthiness criterion in this dissertation.At the beginning of the dissertation, recent developments of crashworthiness optimization are briefly summarized, and multi-objective optimization, thin-walled components optimization and researches on high energy-absorption foam materials are also summarized. Then, the main theoretical backgrounds are introduced, such as explicit finite element technique, design of experiment, response surface method and analysis of variables. After that, these theories are used to analyze and optimize some straight thin-walled beams. In addition, the space profiles with S-shaped and V-shaped neutral axis and foam-filled thin-walled beams are also considered and optimized, which make the research conclusions more practical.Thin-walled components with square or circular cross-section are the most classical energy-absorbing structures. Redhe, Forsbers, Nilsson and Kim have ever paid much attention to the researches of these traditional profiles under the crashworthiness criterion. Based on others'fruits, in this dissertation square cross-sectional thin-walled beams are firstly optimized with the sectional width and thickness as design variables, and with structural specific energy absorption as objective function. The influence of the design variables on the specific energy absorption of single-cell, double-cell, triple-cell and quadruple-cell are summarized. Secondly, single-cell and triple-cell hexagonal sectional profiles are optimized with crashworthiness criterion. Thirdly, tapered profiles of circular cross-section together with profiles of end-taper are analyzed and optimized with multi-objective function. Finally, space profiles with S-shaped and V-shaped neutral axis are optimized with multi-objective functions under crashworthiness criterion. In addition, foam-filled thin-walled beams with square cross-sections and taped foam-filled thin-walled beams are also considered and optimized in the field of crashworthiness.In the dissertation, explicit finite element technique together with response surface method is used to solve contact-impact problems, which have been proved to be a high efficiency method and the fitting results of which are very accurate. The objective and constraint functions obtained by using response surface method can be solved and the optimal design parameters can be obtained quickly. Meanwhile, conclusions of the dissertation can also be an important reference for the crashworthiness optimization of the car body in the future.