Research on multiaxial fatigue life of metro bogie frame with welding defects

As a critical component of metro vehicles, welded bogie frames often develop fatigue cracks at welds during operation, significantly leading to a shorter actual life than originally designed. This study focuses on the motor hanger weld area of the bogie frame and is conducted from the perspective of practical maintenance and inspection requirements. For surface cracks, the critical plane method and strain energy density damage parameter were applied to establish a fatigue life prediction based on strain amplitude-life relationships. For internal defects, the remaining fatigue life under multiaxial stress was simulated in Franc3D using a sub-modeling approach. Results indicated that welding defects can significantly reduce bogie frame life. The analysis provides theoretical support for optimizing bogie maintenance strategies.