Study On Durability Of Auto-body Joints Based On Simplified Vehicle Model

With rapid development and fierce competition in the automobile industry, the demand for the stiffness, strength, durability and safety of the auto-body is higher and higher. This trend requires us to adopt the efficient method to design the structure of the auto-body in the conceptual design phase, which could not only ensure the quality and performance of vehicles, but also shorten the designing cycle and reduce producing costs. In the stage of conceputual design, subjected to the types and the shapes of the vechiles, the layout and the size of the auto-body has little room to change, while the key section and joint structure of the auto-body has more room to do design. Besides, the joints are often the fragile areas of the auto-body. Therefore, it is imperative to do the durability design for the key structrues of the auto-body at the early stage, which will contribute to improving the efficiency of the auto-body design.According to the problems exisiting in the conceputual designing phase, such as the little information about the auto-body structure parameter, the difficulty to build the detailed and complete vehicle finite element model and the impossibilty to conduct the traditional durability test for vehicles, based on the actual structure of the joints, an auto-body conceptual simplified FEA model (ZJ as an abbreviation) is proposed. While the establishment of vehicle durability test model, the simulated analysis for the vehicle durabilty in the virtual road test, and the analysis for fatigue life of the key joints structure, and the optimization in designing were also be accomplished in the research. The main aspects of the studies are as follows:(1) Research status of the conceptual design of auto-body structure, the joint structures and auto-body fatigue durability in the worldwide were introduced. And it put forward the improtance to do the durability design for the key structures of the auto-body.(2) Proposed a simplified FEA model for conceptual auto-body which is based on the actual joints. According to the demands of the layout size of automotive body, the ZJ model was set up by using the basic car’s parameter from the data base of key-sections character, which was composed of actual joints, beam elements and large-size shell elements. The feasibility of the modeling method was validated through analysis of mode, torsion stiffness, bending stiffness of the model, and comparison between characteristic parameters of the later detailed FEA model. The modeling and validation process of ZJ model proves that ZJ is easy-to-build, flexible-to-modify and meet the requirements of the auto-body performance analysis. ZJ model could provide important guidance to subsequent design.(3) We established the vehicle durability virtual testing model, with the ZJ as the dominant position including vehicle suspension and tires. Based on the virtual durability test environment of virtual proving ground, considering structure and material nonlinear characteristic, with comprehensive durability virtual road which has real load as input, the transient response analysis of the vehicle system was carried out to obtain the dynamic stress-strain time history of the auto-body. The C-upper-joint of a new type of vehicle could be taken as an example,the fatigue life analysis and modification design of T-type joint structure are performed by using strain-life method,and the feasibility and validity of the analysis is proved by the road test later .Researches of this paper show that the construction method of ZJ model and the method of vehicle durability virtual test which based on virtual proving ground could effectively solve the problem of establishing detailed vehicle FEA model and the impossibility of conducting the traditional durability test. The study will promote the auto-body structure design and durability research in the conceptual designing process, and has stronger engineering practicability.