Study On Vibration Fatigue Of Welded Frame Of Intercity Emu Based On Modal Structural Stress Method

Intercity EMUs is characterized by the large capacity,short distance between stations,frequent acceleration and deceleration and small curves,which makes the service environment of intercity EMUs worse than that of high-speed railway,and the vibration fatigue problem caused by wheel/rail high-frequency excitation is more prominent.As an important bearing component of railway vehicles,the structural reliability of bogie frame become the essential to the operating safety.Therefore,how to accurately evaluate the vibration fatigue life of bogie frames becomes particularly important.Combining the structural stress method and modal superposition method,a structural stress calculation method based on the modal method is proposed in the paper.Together with rigid-flexible coupling dynamic model of vehicle system,the vibration fatigue of intercity EMU bogie frame is studied in detail.The main conclusions are as follows:(1)Based on the structural stress method,the mesh insensitivity of structural stress of typical welded joints and bogie frame were studied.The modal stress superposition method is applied to the superposition of weld modal node forces,and a structural stress calculation method based on modal method is developed.Based on a typical welded joints,the structural stress of welded seam obtained by using the quasi-static method and the modal method was compared,and the influence of external excitation frequency on the structural stress is analyzed.The results showed that the structural stress calculation method based on the modal method can consider the influence of modal response on structural stress.The inertial release mode(IRM)can be used to correct the contribution arising from high-order vibration modes.(2)Based the modal structural stress method and the rigid-flexible coupled dynamic model,a vibration model based the random vibration was established,so as to identify the dynamic-critical position for bogie frame.Considering the measured random vibration,ten critical position for bogie frame were identified.The weld seams in the side beam are identified as the most critical position in the bogie frame,and the domination frequency of 47.8,499.7and 594.7 Hz show the greatest contribution to the stress of weld seam.Moreover,the contribution of each mode to the structural stress was further investigated,and the first torsional mode of bogie frame,the lateral bending of side beam,vertical bending of transverse beam as well as the out phase lateral bending for side beam were identified the most critical vibration modes.(3)Based on the rigid flexible coupling dynamic model of vehicle system,the characteristic stress spectrum and fatigue life of bogie frame under typical operating conditions were studied.The results showed that the vehicle operating speed,curve superelevation and curve radius have a significant influence on the dynamic stress of the welds at the critical positions of the bogie frame,in which the welds between the upper cover plate of the side beam and the inner vertical plate and the welds of the anti-roll torsion bar seat have the greatest damage per kilometer.The damage at critical positions was evaluated based on the nominal stress method and the principal S–N curve method respectively.The damage calculated by the principal S–N curve method was conservative compared with the results obtained by nominal stress method,and the weld damage safety margin of the anti-roll torsion bar seat calculated based on the principal S–N curve method is lower.