采用超声疲劳试验方法对SMA490BW钢焊接接头的超高周疲劳性能进行研究，通过X射线应力仪对焊接试样残余应力进行测试，采用扫描电镜对疲劳裂纹的萌生、扩展及疲劳断裂机理进行观察和分析. 结果表明，SMA490BW钢母材的疲劳性能远高于焊接接头，在1×108循环周次条件下，接头的疲劳强度为141 MPa，仅为母材的44.2%. 接头裂纹主要萌生于焊趾表面缺陷处，疲劳断裂机理表现为准解理断裂, 并伴有塑性变形痕迹. 焊趾处几何不连续造成的应力集中和焊缝及其附近区域一定的残余拉应力，以及接头各微区组织和性能的不均匀性，是导致焊接接头疲劳性能偏低的主要原因.
Very high cycle fatigue properties of SMA490BW steel welded joints for train bogie were investigated by the ultrasonic fatigue testing method. The residual stress of the welded joint was tested through X-ray stress tester. Fatigue crack initiation, propagation and fatigue fracture mechanism were observed and analyzed using scanning electron microscopy. Experimental results show that fatigue property of SMA490BW steel base metal is much higher than that of the welded joint. Under the condition of 1×108 cycles fatigue life, the fatigue strength of welded joint is 141 MPa, while that is only 44.2% of base metal. Fatigue cracks of welded joint initiated mainly at surface defects of welded toe, and the fatigue fracture mechanism is exhibited as quasi-cleavage fracture, which accompanied by the traces of plastic deformation in the fracture surface. Residual tensile stress and stress concentration at welded toe, and non-uniformity of microstructure and properties in welded zone are the main factors causing low fatigue property of the welded joint.
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