Full life fatigue assessment method based on damage tolerance model coupled with periodic maintenance for welded joints of bogie frames

Purpose This study aims to propose a discrete damage tolerance full life fatigue assessment method considering periodic maintenance behaviors, to achieve accurate assessment and life prediction of fatigue damage evolution at the swivel arm mounting seat welds of electric multiple unit (EMU) bogie frames. Design/methodology/approach Firstly, a finite element model of the bogie frame is established, and load cases are applied according to UIC 615–4 and International Institute of Welding (IIW) standards. The hot spot stress method is used to identify critical weld regions and calculate crack initiation life, and the engineering detectable crack size of 0.5 mm is defined as the end of the initiation stage. Subsequently, 2 mm is determined as the maintenance limit based on structural characteristics and domestic maintenance specifications. Finally, a discrete damage tolerance model embedded with 1.2 million kilometers periodic maintenance nodes is established and coupled with continuous crack propagation to realize quantitative full life fatigue assessment from initiation to maintenance limit. Findings The results show that maintenance interval and initial crack size have a significant coupled effect on remaining life and safety margin. Under the 1.2 million kilometers standard maintenance interval, the safety margin for the 0.5 mm initial crack case is close to the critical threshold. When the initial crack size increases to 1.0 mm or the maintenance interval is extended to 1.5 million kilometers, the structure will face a missed detection risk across maintenance intervals. Originality/value This method provides an engineering approach for maintenance strategy optimization and full life fatigue assessment of EMU bogie frame welds.