钢轨踏面低塌对轨底锈蚀坑受力及疲劳性能的影响

Influence of Collapsed Rail Welding Joint and Corrosion Pit on Safe Service of Rail

对一断裂钢轨案例进行失效分析,发现断口位于距闪光焊焊缝中心(最大低塌量0.7 mm)60 mm处,裂纹起源于轨底下表面0.43 mm深的锈蚀坑底部。依据失效钢轨伤损特征和力学理论公式,建立轨底锈蚀坑受力分析模型,并基于4参数经验公式计算相应伤损特征下轨底处的疲劳极限,研究轨底锈蚀坑和踏面低塌2处伤损的发展对锈蚀坑处应力及疲劳极限的影响规律。结果表明:钢轨踏面低塌激励的附加冲击力会造成附近轨底锈蚀坑应力增大,而踏面低塌降低循环载荷应力比和轨底锈蚀坑应力集中效应的双重作用导致服役钢轨的疲劳极限σ_(r)下降,当锈蚀坑处轨底最大拉应力σ_(d)大于疲劳极限σ_(r)时,锈蚀坑底部易于萌生疲劳裂纹而导致钢轨断裂失效。按钢轨断裂时轨温和失效分析中测量的钢轨伤损数值计算,σ_(d)和σ_(r)分别为130.8 MPa和101.0 MPa,而踏面无低塌时σ_(d)和σ_(r)分别为94.6 MPa和118.5 MPa,因此钢轨在踏面低塌和轨底锈蚀坑两者共同作用下发生断裂失效。为保证钢轨的安全服役,轨底锈蚀坑应力集中系数K_(t)和接头最大低塌量λ须低于临界值。

The failure analysis for a fractured rail in heavy haul railway was carried out.It was found that the fatigue fracture occurred near a collapsed flash welding joint(with a distance of about 60 mm).The crack initiated from the lower surface of the rail bottom,where obvious corrosion pits(0.43 mm in depth)could be observed.Combined with the damage characteristics of the rail,the mechanical analysis model of the rail bottom corrosion pit was established.The fatigue limitσ_(r)of the rail bottom pit was also calculated based on an empirical formula.Furthermore,using the stress concentration factor Ktof the corrosion pit and the collapse depthλas variables,the superimposed influence of these two damages on the stress and fatigue limit about the rail bottom pit was studied.The results show that the collapse excited additional impact force increases the corrosion pit stress on the nearby rail bottom.Meanwhile,under the dual influences of reduced cyclic stress ratio caused by collapse and the stress concentration of corrosion pit,the fatigue limitσ_(r)decreases.When the maximum tensile stress of the rail bottomσ_(d)is greater thanσ_(r),fatigue crack is prone to initiating from the bottom of the corrosion pit,resulting in the rail failure.According to the damage values and the rail temperature measured on the failure rail,σ_(d)andσ_(r) are 130.8 MPa and 101.0 MPa,respectively,while the two are 94.6 MPa and 118.5 MPa when the joint has no collapse,thus the combined influences of welding joint collapse and rail bottom corrosion pit lead to the rail fracture.In order to ensure the safe service of the heavy haul rail,the stress concentration factor K_(t) of the corrosion pit and the collapse depthλshould be lower than the critical values.