中文摘要：

采用自行研制的TJu．HJ—I型超声疲劳试验装置对EH36钢无余高焊接接头在超长寿命区间的疲劳性能进行研究．试验结果表明：在10^7循环周次以后试件仍然会在焊接接头发生断裂，并且s—N曲线仍呈下降趋势，没有出现传统意义上的疲劳极限．尽管不存在余高，焊接接头表面不存在应力集中，但是大部分试件仍然在焊接接头处断裂．通过扫描电子显微镜分析断口可以观察到，裂纹源大部分处于表面机械加工微痕及次表面微观缺陷处．另外，焊接接头中缺陷引起的“鱼眼”与母材中的“鱼眼”并不完全相同，前者的鱼眼中不存在视觉黑暗区．

英文摘要：

The super-long life fatigue properties of EH36 steel butt welds ground flush were studied by the self-made TJU-HJ-I type ultrasonic fatigue test device. Fatigue test results show that fracture still occurs in the welded joint after 107 cycles, and that the S-N curve descends continuously. There is no such fatigue limit as described by the traditional fatigue conception. Although welding residual height does not exist and stress concentration does not exist on welded joint surface, fracture still occurs in the joint. Scanning electron microscope （SEM） analysis shows that fatigue crack mostly initiates from machining micro mark and microstructure defects in subsurface. Besides, the ＂fish-eye＂ induced by the defects in welded joint is not all the same as that in the base steel. The optical dark area （ODA） does not exist in the former ＂fish-eye＂.