Study on Fatigue Strength of Welds in Bogie Frame Based on Structural Stresses

In order to solve problems in application of the permissible fatigue strength data for welds in bogie frames, comparisons of different structural stress approaches and data were carried out. The relations and differences in the measurement methods of weld structural stress, permissible stress amplitude, survival probability of design value, mean stress modification, fatigue strength improvement of weld improvement and determination of limit permissible stress were compared. And the fatigue diagrams and S-N curves based on measured structural stress for Q345 steel welds were established. From the research conclusions, the fatigue diagrams and S-N curves based on measured structural stress for Q345 steel welds were established. The results show that the measuring method of weld structural stress provided by B12/RP17, the end of stress gauge, length of 6 mm, should be against the weld toe, can be continually used. It is recommended that the basic two data sets of IIW (International Institute of Welding) FAT100 and FAT90 can be used as reference to establish the more reasonable permissible fatigue strength data based on structural stress along with its mean stress and fatigue strength improvement of welds modification methods. For a fatigue diagram with 2 × 10⁶ stress cycles, the limit permissible stress can be determined by reducing the yield strength of the base material by the corresponding safety factor according to DVS 1612.