Stochastic Vibration And Fatigue Analysis Of Frame For Model CA6120U22DI Bus

Bus frame is main loaded parts of buses, whose characteristics of stiffness, strength, model dynamic and fatigue characteristics have great influences on the safety, traveling comfort, stability and fatigue life of buses. So the researches on these characteristics of frame are of great importance to the buses design and contribute to the economic significance and safety to the passengers and society.Model CA6120U22D1 buses were produced by Changchun bus Company in 2004. But after five years in service, some crakes were found on the frame of some buses. In order to find out the reasons for the crakes, the frame for model CA6120U22D1 bus was taken as main research subjects in this paper. Based on the technologies of CAD, Finite Element Analysis and Fatigue analysis, one FE model of the frame for model CA6120U22D1 buses was established. And static analysis, stochastic vibration analysis and fatigue analysis were carried out to analyze the real reasons for the failure of the frame.Static analysis was carried out under particular load conditions to obtain the deformation and stress distribution of critical positions of the frame to check the stiffness and strength and the safety of the frame.Based on the finite element dynamics, the vibration modes of the bus frame with pre-stress the research were calculated to get the model characteristic such as inherent frequency. After that, according to the road grading standard of GB7031-87 for mechanical vibration-road surface profiles-reporting measured data, the road roughness power spectrum density can be obtained. Based on the Fourier inversion, power spectrum density in frequency domain can be simulated. Then stochastic vibration analysis was carried out by inputting road power spectrum density into the FE model to obtain the displacement, velocity and acceleration responses on the critical locations of the frame. After the analysis, the reasons why the crakes came out were found out.On the foundation of static analysis and stochastic vibration analysis, the stress of the frame can be obtained. The finite element results and simulated dynamic load, as well as the S-N curve of the material were applied on the model. Then S-N fatigue analysis was carried out under quasi-static condition to calculate the fatigue life and the comparison of the critical positions was made between the static analysis and S-N fatigue analysis to check the critical positions. Corresponding to stochastic vibration analysis, stochastic fatigue analysis was carried out while the frame traveling on the worst conditions. The fatigue life of the frame under special conditions in stochastic fatigue analysis was obtained and fatigue failure of the frame was verified.