Crashworthiness Research And Optimal Design For Vehicle Frame's Safety

Safety, energy conservation and environmental protection are the three principal problems for the development of automobile industry in the 21^st century. Frame is the most important energy absorption component for those vehicles with non-bearing type of body structure during frontal or rear collisions. More than 50% of the impact energy is absorbed by the frame. So the research of the frame's collision characteristics is of great significance.This paper carries on a thorough research of a sport utility vehicle's crashworthiness. Through cleaning up geometry, extracting midsurface, dividing into grids, controlling quality of the elements, the finite element model of automobile frame is established by using thin shell elements. Through tensile testing, the stress-strain curves of frame's parts are obtained based on the Johnson-Cook constitutive equation. Bending stiffness, torsional stiffness and free modal of the frame is analyzed, based on the finite element model. The results show that the values of the stiffness and mode's frequency are sufficient for design. From collision of automobile to fix wall, frontal collision of automobile to automobile, offset frontal collision of automobile to automobile, offset frontal collision of automobile to fix wall, this paper studies the mechanics analysis method of the automobile collisions. The results show that the structure parameters are of great importance for automobile collisions.Then this paper focuses research on the following typical thin-walled rail Structures: S-shaped rail, induced trough structure and the rail structure with variable cross-section. An S-Rail impact model is extracted from a true rail used in vehicle frame. Several parameters are proposed as the model variables. Response surface model is interfaced with genetic algorithms to find the optimal parameter values. The relationships between energy absorption and the proposed variables are revealed. S-shaped rail absorbs much energy after its optimal design. An effective structure of deformation induced groove is proposed by analyzing a variety of deformation-induced structural features. Optimal design is carried on the iduced groove to improve its dynamic crashworthiness characteristics of energy absorption. Based on the induced groove, a thin-walled rail with variable section is proposed by comparing a variety of thin-walled rails with different section features. Then the rail is used in the front of a vehicle's frame. Optimal design method is presented and utilized to obtain optimum crashworthiness design of the thin-walled rail with variable section. The methodology adopted in this research makes use of Design of Experiments (DOE), Finite Element Analysis (FEA), Artificial Neural Networks (ANN) and Genetic Algorithms (GA). The relationships between energy absorption and the proposed variables are revealed and the optimal results are verified through the finite element analysis of thin-walled rail's collision.Base on optimal design of the typical thin-walled rails, the crashworthiness of a sport utility vehicle's frame is improved. The path of the force transmission becomes more reasonable after the frame's optimization during the impacts. And the passive safety of the vehicle is greatly improved...