Analysis of the modal effects on vibration fatigue in a full-scale welded carbody for high-speed train

Structural fatigue failure is closely linked to vibration modal characteristics and dynamic response. Therefore, analyzing the relationship between modal properties and dynamic behavior is essential for fatigue-resistant design. First, a full-scale finite element model of the vehicle body is developed, taking into account the connections between the carbody and auxiliary suspension equipment. The modal characteristics of both the empty and fully loaded vehicle bodies are obtained and compared to identify the causes of local modal phenomena. Then, using modal decomposition, the modal displacement responses in the modal coordinate system are calculated under the influence of random multi-axis load spectra. The results confirm that the selected truncation order falls within an acceptable error range. Furthermore, the impact of each mode on fatigue damage is evaluated to identify critical modes. Based on the modal superposition method, fatigue damage at weld locations is calculated using two different stress-based approaches, and the results are compared. The findings show that selecting the truncation order according to the trend of relative error is effective. In addition, modes with higher modal displacement responses have a greater influence on fatigue damage. For fatigue life assessment, the structural stress method proves to be more accurate and advantageous than the nominal stress method