Analysis Of Strength Of Whole Bus Frame And Local Stress Concentration

This thesis first comprehensively introduced the domestic and international present research state and the development trend of the FEM (Finite Element Method) in the city bus design and the stress analysis research. It elaborated the application of the FEM in the strength and stress concentration analysis of the bus body frame. The domestic research started later than abroad lags behind now, so we need to expedite the research speed to catch up the level of the international research.According to the requirement of the research project, and based on the elaboration of the typical city bus structure, the thesis analyzed the characters of city bus body frame component and the early failure of the bus, which has occurred only after about 100,000 km driving. We also proposed the method to solve the early failure problem.Based on those researches above, three modeling methods of the bus body frame nowadays by using FEM were studied, and the characteristic differences as well as the advantage and the disadvantage of them were analyzed. How to choose and use them in the practical modeling application was also stated. According to the actual structure and the real size of the defective bus, this thesis has accurately established the bus body frame model using the board-shell element, carried on the analysis of the body frame strength and stiffness, and obtained the stress distribution and concentration result of the bus body frame. Finally we found the reason, which causes the body frame early failure problem.This thesis has also studied the location, the partial connecting detail, the structural style of the local bus-bracket, and other factors, which have the overall influence on the strength of the body frame. The design to improve the real structure of bus based on the synthetic study result above was also conducted. Finally a convenient, feasible, inexpensive research scheme for the bus maintenance and redesign was proposed. For the defective bus service and the new bus design, this scheme provided the theoretical and technical guidance for the users, reducing greatly the economic loss of the bus factoryand the city bus user.The local stress concentration of the bus body frame was also studied. For the bus-shackle structure near the early failure spot, this thesis established the real 3D full-scale mockup, and spliced it in the bus body frame model founded by the unique board-shell elements to calculate the local stress distribution and the stress concentration, using it to carry on the comparison with the obtained result of the simplified mechanic model. This thesis also studied the influence of the spacing, which is between the central action point on the shackle and the exterior plate of the chassis frame side rail, because the spacing influenced the local stress distribution and the stress concentration of the bus body frame and the chassis frame, and the related variational tendency was summarized. Meanwhile, the method of secondary calculation and secondary analysis was used to study the situation of the stress distribution and concentration near the pins holes on the early failure spot of the frame. Those results provide the reference to the analysis of the crack in the partial structure. This thesis simultaneously studied the application scope and the skill of the sub-modeling analysis method during those analyses above. These researches and discussions can provide the reference and beneficial help, for choosing and establishing the computation model of the city bus body frame by using the FEM, analyzing the bus body frame strength and the local stress concentration analysis, reducing the weight of the city bus body frame, improving the loading capacity of the city bus.