钢轨滚动接触疲劳多裂纹相互影响

Interactive Influence on Multiple Head Checks Propagation in Rail

通过X射线计算机断层扫描得到曲线外轨轨距角-轨肩多条滚动接触疲劳裂纹的内部形态,采用栅格法得到真实裂纹的开口和尖端边界点,建立真实裂纹形态数学模型。以我国某重载线路通过总重约62 MGT时小半径曲线外轨轨肩-轨距角裂纹为例,分析了多条裂纹存在下的裂纹尖端应力强度因子变化及裂纹数量对其的影响。结果表明:裂纹最容易沿与轨顶纵向呈10°~30°的角度向钢轨内部扩展;不论何种条件,KⅠ始终小于零,表明此处裂纹不受张开效应扩展;轮轨接触斑以作用在裂纹中部的方式通过裂纹区域时,裂纹尖端各点的应力强度因子KⅡ>0,KⅢ沿裂纹尖端从轨距角一侧到轨顶中心一侧呈由正到负的趋势,表明此时裂纹的扩展形式主要由滑开型和撕开型复合而成,且裂纹在轨距角扩展的部分扩展较快;多裂纹的存在会促进裂纹的滑开和撕开效应,该促进作用随裂纹数量的增加而增强。多条裂纹的存在会使得裂纹尖端的应力强度因子增大,中间裂纹受到两侧裂纹的影响较明显。在进行裂纹扩展预测时,应至少考虑3条裂纹。

Head checks(HCs)at rail gauge corner and shoulder were inspected by X-ray computed tomography scan technology(CT scanning).The boundary points at the mouth and tip of the real HCs were obtained by grid method to establish the numerical model of the real HCs.Taking the HCs at the gauge corner and shoulder of the high rail in a heavy-haul railway sharp curve with traffic gross tonnage of about 62 MGT as an example,this study analyzed the transformation of the stress intensity factors(SIF)at the tips of multiple HCs and the effect of the crack number on them.The results show that the HCs are more likely to extend with an orientation of 10°-30°with respect to rail longitudinal direction,always less than 0 under any condition,indicating that the crack is not extended by Model I(opening).HCs are greater than 0,and the trend of is reduced from positive to negative along rail gauge corner to crown when contact patches pass by the crack central mouth,which shows that the HCs is mainly composed of Model II(sliding)and III(tearing).The existence of multiple HCs will promote their propagating as Model II and III,and the influence will be enhanced with the increase of crack number.Compared with the single crack,SIFs at the tips of multiple cracks will increase,and the SIFs at the tip of the middle crack will be greatly influenced by adjacent cracks.Therefore,at least 3 cracks are recommended in crack propagation modeling for crack prediction.