大气预腐蚀下ER8C车轮钢的疲劳寿命评估

Fatigue Life Estimation of ER8C Wheel Steel Subjected to Atmospheric Pre-corrosion

随着高速列车车轮服役里程的增加,车轮辐板持续遭受潮湿大气甚至海洋大气环境的考验,点蚀成为车轮失效的主要原因之一.论文首先在大气自然环境下对ER8C车轮钢高周疲劳试样开展为期180天的曝晒(预腐蚀)试验,随后进行表面形貌和疲劳性能表征.结果表明,预腐蚀后车轮钢的疲劳极限为387MPa,相比光滑试样下降12%;这主要是由于预腐蚀造成的腐蚀坑使试样表面局部应力集中,加速了疲劳裂纹萌生.采用激光共聚焦显微镜统计预腐蚀试样表面蚀坑尺寸,使用由均值蚀坑尺寸计算得到等效初始缺陷尺寸(EIFS),对预腐蚀车轮钢试样的疲劳寿命进行预测,避免腐蚀疲劳裂纹萌生以及短裂纹扩展对疲劳寿命预测的影响;预测结果与实验结果较为符合,证明了该方法的可行性.论文的主要结论是,通过统计试样表面蚀坑尺寸的均值来获得EIFS的方法,可以计算得到大气预腐蚀后车轮钢的剩余寿命,这验证了EIFS方法在大气预腐蚀下材料疲劳寿命研究中的适用性.

With the increasing of high-speed railway mileage,the wheel webs are subjected to longterm exposure to humidity and even marine atmospheres,making corrosion pits being one of the main causes of wheel failure.In this study,to more closely simulate the actual working conditions,high-cycle fatigue specimens of ER8Cwheel steel are treated with 180-day pre-corrosion under atmospheric conditions.That is different from the artificial accelerated corrosion conditions employed in many other studies.The surface morphologies,sizes,and distribution of corrosion pits are characterized by scanning electron microscopy(SEM),followed by the high-cycle fatigue tests.The results show that the fatigue limit of precorrosion steel is 387MPa,which is 12%lower than that of the uncorroded steel.This is mainly due to the local stress concentration caused by the corrosion pits on the specimen surface,which accelerates the fatigue crack initiation.The sizes of the pits at the specimen surface are measured using laser confocal microscopy,and the mean pit depth,width and the shape ratio of depth to width are obtained.Finally,the equivalent initial flaw size(EIFS),calculated from the mean pit depth and width,is used to predict the remaining life of the wheel steel.This method avoids the difficulties of fatigue crack initiation and short crack growth modeling on the prediction of fatigue life.The calculated remaining life of the wheel steel is more in line with the experimental results and proves the feasibility of the method.It is concluded from this study that the EIFS can be obtained by counting the mean pit depth and width on the specimen surface,and the method of EIFS could be used to calculate the remaining life of wheel steel after atmospheric pre-corrosion.This verifies the applicability of the EIFS method in predicting the fatigue life of materials subjected to atmospheric pre-corrosion.