HXD2机车转向架拉杆座角焊缝疲劳失效机理

Fatigue failure mechanism of fillet weld in tie rod seat of HXD2 locomotive bogie

针对HXD2型电力机车在某穿越秦岭山脉线路服役中多台次拉杆座角焊缝出现裂纹的问题,进行了试验与仿真分析。发现裂纹表面有明显疲劳辉纹,表明角焊缝服役中发生疲劳失效;焊缝根部是疲劳起裂位置,有多源起裂形貌特征;起裂后裂纹从中心向两侧扩展、从根部向焊缝表面扩展,在接头横截面上裂纹路径与水平方向夹角近似为45°;统计分析和仿真计算表明,角焊缝裂纹的发生与拉杆座/基板之间的间隙值有关联性,根部间隙越大,则角焊缝抗疲劳性能越差;分析其主要机理是间隙较小时,焊缝受压后拉杆座底面与构架基板表面更容易发生接触,接触后基板表面分担部分载荷。因此,间隙较小时,焊缝应力幅较小;而间隙较大时,不仅应力幅较大,而且在焊根处易出现末端尖劈形貌。

Aiming at the problem of weld cracks in tie rod seat of HXD2 electric locomotive running on a line crossing Qinling Mountains,the method of combining test and simulation was used to study the problem.Fatigue striations were found on the surface of cracks,which indicated that fatigue failure occurred in the fillet weld of tie rod seat during service,and cracks initiated at the root of weld and were characterized by multiple sources.After initiation,cracks expanded from the center to both sides and from the root to the surface of weld,and the angle between crack propagation path and horizontal direction was approximately 45°on the cross section of welded joint.Statistical analysis and simulation showed that occurrence of fillet weld crack could be related to gap value between tie rod seat and substrate,and the larger the root gap was,the worse the fatigue resistance of fillet weld was.Analysis showed that main mechanism might be that when the gap was small,the bottom surface of tie rod seat was more likely to contact with the surface of frame substrate,and the substrate surface shared part of the load after contact.Therefore,the stress amplitude of weld was small when the gap was small,but when the gap was large,not only the stress amplitude was large,but also the wedge-shaped gap end was easy to appear at weld root.