基于结构应力的转向架构架焊缝疲劳强度研究

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

为了解决现行标准中转向架构架焊缝容许疲劳强度数据存在的问题,针对当前的各种结构应力方法和数据,就其在焊缝结构应力测试、容许应力幅、设计值存活率、平均应力修正、焊缝修整疲劳强度提高及极限容许应力确定等方面的关系和差异进行对比,并构建了Q345钢焊缝基于实测结构应力的疲劳图和S-N曲线.结果表明:转向架构架焊缝结构应力的实测可沿用B12/RP17规定的方法,即采用6 mm长的应变片并将其前端紧靠焊趾边缘布置;建议借鉴IIW (Intemational Institute of Welding) FAT100和FAT90两组基本数据,并应用其平均应力和焊缝修整疲劳强度提高的修正方法,构建更加合理的基于实测结构应力的焊缝容许疲劳强度数据;对于2×10~6次循环数对应的疲劳图,极限容许应力可参考DVS 1612规定的方法,由母材屈服极限除以相应的安全系数确定.

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 2×10^6 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.