Design And Optimization On The Crashworthiness Of Metal Thin-Walled Tube

Safety, environment protection and energy conservation are the inevitable trends of automotive technology development in the21st century. Meanwhile, the method to improve the crashworthiness of vehicle has been a hot issue of the automotive passive safety protection. As the most traditional and effective energy-absorbing structure, the metal thin-walled tube has been widely used in the design of automotive safety. Under the requirement of light-weight vehicles, the structure using less material to absorb more crash energy has become as a hot spot of vehicle design. In recent years, many researches have been dedicated to improve the crashworthiness of metal thin-walled tubes and have provided a series of results. On the basis of previous researches, the crashworthiness of the metallic thin-walled tube is discussed and optimized by using the explicit finite element technique software LS-DYNA and response surface methodology.Firstly, the recent progress in the study of the metallic thin-walled tube structures is reviewed. Then a brief introduction to the basic equations of finite element method and contact collision algorithm is given. Meanwhile, the methods of experiment design and the approximate models used in the crashworthiness optimization of the metallic thin-walled tube are outlined. To improve the crashworthiness of the metallic thin-walled tube, the absorption structure is optimized by the explicit finite element software LS-DYNA and response surface methodology. Then, the effect of geometric parameters on the energy absorption of the prescribed structure is analyzed.1) Based on the fact that the absorption area of the square cross-section thin-walled tube is mainly in the corners, two kinds of polygonal point absorption structures are designed in this work. The specific energy absorption and initial peak force of the polygonal point absorption structure are taken as the optimization objectives. Full factorial experiment design method and response surface methodology are used to optimize the prescribed structures. The results show that, the specific energy absorption and larger initial peak force of the structure are higher, when the tube sheet has a larger width.2) A double-layer absorption structure combining a large with a small cross-section thin-walled tube is designed and four thin sheets are added between the two thin-walled tubes with a square cross-section. The effect of the added sheets on the energy absorption of the designed structure is analyzed by using the explicit finite element software LS-DYNA. The results show that: the added sheets can effectively improve the crashworthiness of the double-layer absorption structure, and enhance the interaction between the inner and outer square tube.3) To discuss the effects of specific energy absorption, initial peak force, second peak force and other factors on the safety of automobile, a multi-objective crashworthiness optimization problem is formulated and solved in this work. The results show that: the optimized structure can improve the total energy absorption and specific energy absorption, and avoid a higher initial peak force.4) Since the square cross-section tube has a degenerated stability and the circular cross-section tube has high specific energy absorption, a combination-type energy absorption structure which contains a large square cross-section and a small circular cross-section tube is designed and its crashworthiness is analyzed by the explicit finite element software LS-DYNA. The results show that: the larger the inner tube diameter and the length of inner and outer tubes are, the smaller the specific energy absorption of the combined structure.