SMA490BW钢对接接头高周疲劳性能的机理探究

Mechanism of Improving the High Cycle Fatigue Property of SMA490BW Steel Butt Joint

通过设计对比试验系统地分析应力集中、晶粒细化、残余应力等因素对转向架用SMA490BW钢对接接头高周疲劳性能的影响,并得出占据主导作用的因素。借助扫描电镜观察疲劳断口,探究对接接头冲击前后的失效模式。结果表明:经超声冲击或机械打磨处理后,试样的疲劳寿命均得到不同程度的提高。将焊缝余高彻底磨平对接头疲劳寿命的增益效果最为显著,其疲劳寿命相比原始对接接头可提高近百倍。改善应力集中、细化表层晶粒、引入残余压应力对对接接头延寿的贡献占比分别约为58%、29%和13%。对接接头的疲劳失效大多始于焊趾表面,经超声冲击处理后,疲劳裂纹源可能由材料表面转向内部缺陷。

The influences of stress concentration,grain refinement and residual stress on the high cycle fatigue of SMA490 BW steel butt joints were systematically analyzed by the comparative fatigue test,and the dominant factor was obtained.The fatigue fracture morphology observation was conducted through a scanning electron microscope to determine failure modes of the welded joints with and without ultrasonic impact treatment（UIT）.The results showed that both UIT and mechanical polishing treatment could improve the specimen＇s fatigue life to certain extents.And eliminating the weld reinforcement will lead to a remarkable promotion of welded joint＇s fatigue life（nearly 100 times larger）compared with the original welded joints.It can be concluded that the contribution ratios of stress concentration,grain refinement and residual compressive stress on the life extension of the welded joint are about 58%,29% and 13%,respectively.The fatigue failure of welded joints mostly comes from the surface of weld toe,and the fatigue crack initiation position shift to the internal defect after UIT.