Vibration fatigue analysis of high-speed railway vehicle carbody under shaking condition

A method called modified modal superposition method (MMSM) for calculating the vibration fatigue dynamic stress of carbody under shaking condition is proposed. In MMSM, each external load is divided into low frequency component and high frequency component according to critical frequency (CF), which is used to separate whether the external load causes resonance effect of the structure, then traditional quasi-static method (QSM) and modal superposition method (MSM) are adopted to deal with the two load components respectively. During the simulation, QSM is used to ensure the integrity and accuracy of the structural stiffness under quasi-static condition, while MSM can consider the dynamic characteristics of the structure in resonance state. At last, the fatigue strength of the carbody was carried out based on the stress calculated according to cumulative damage method. The calculation results show that the fatigue life of carbody under shaking condition is significantly reduced to 81,450 km, far less than the design life. The damage of the stress obtained by MMSM is far greater than that from traditional QSM, even in the new wheel condition, the damage obtained by QSM is too dangerous. For the stress obtained by MSM, generally in the low-frequency region, the stress level is higher than that obtained by QSM due to mode truncation, especially for the average stress. So QSM and MSM are not recommended to evaluate the fatigue strength of railway vehicle carbody.