Research on fatigue damage of metro frame based on effective notch stress

The fatigue failure of metro frame may occur at the weld toe and weld root of the welded joint. Therefore, an effective fatigue evaluation method is needed to analyze the fatigue reliability of the bogie comprehensively. To solve this problem, based on the effective notch stress method, the overall finite element model of one metro frame and the local mesh refinement finite element model of the welded joint between the wing plate of the motor suspension seat and the cross beam were established, and the effective notch stress distribution at the weld toe and weld root of the welded joint was obtained. According to Miner damage theory and the corresponding S-N curve, the cumulative damage of effective notch stress method and nominal stress method were calculated. The results show that fatigue failure is more likely to occur at the root of the joint. In addition, the effective notch stress method is safer than the nominal stress method. For further study the influence of different loads on damage, by comparing the cumulative damage results of each load, it was found that for the effective notch stress, the five loads with large damage are torsional load, motor transverse load, motor vertical vibration load, motor driving load and gearbox vertical vibration load, of which the torsional load accounts for the largest proportion, up to 30%-60%. The safety and applicability of the effective notch stress method in the fatigue evaluation of subway vehicle frame was verified.