Issue 48

B. Chen et alii, Frattura ed Integrità Strutturale, 48 (2019) 385-399; DOI: 10.3221/IGF-ESIS.48.37 388 Fatigue strength analysis of bogie frame The equivalent stress occurring in the bogie frame on exceptional loads should be less than the yield strength of the used material and S=1.1 should be retained in the weld. Under the normal service loads, the mean stress and stress amplitude are calculated on each load and they should be within the fatigue limit diagram. However, the bogie frame of railway vehicle bears vertical, transverse, longitudinal and oblique symmetrical loads during its service, which belongs to the typical multi-axle load state. For this purpose, this paper calculates the stress and amplitude according to the multi-axial stress state-uniaxial stress state transition method provided by ORE B12/RP17. 1 2 （ a ） max   1 2 （ b ） max   min  n  Figure 2 : Determination of maximum and minimum principal stresses The maximum principal stress direction of the structure under all load conditions is taken as the basic stress distribution direction, and its value is calculated as the maximum principal stress max  , as shown in Fig. 2(a). The principal stress under other loading conditions is projected to the determined direction of maximum principal stress, and the minimum principal stress is determined as the minimum principal stress min  , as shown in Fig. 2(b). By calculating the mean stress m  and stress amplitude a  or stress ratio R from the maximum and minimum principal stress values, the transformation from multi-axial stress state to uniaxial stress state is completed. The mean stress m  and the stress amplitude a  are defined as follows max min max min 2 2 m a       + − = = (1) According to Tab. 1 and Tab. 2, finite element analysis of bogie frame is conducted. Fig. 3 displays the maximum utilization rate of all welds under fatigue conditions. The mean stress and stress amplitude are calculated under fatigue conditions, and the results of evaluating the fatigue limit diagram is obtained, as detailed in Fig 4. Figure 3 : Maximum utilization rate plot of fatigue conditions Figure 4 : Fatigue analysis results of bogie frame