滚动接触载荷下车轮钢超高周疲劳实验研究和寿命预测

With the development of high-speed railway in China, many key components including wheels, axles and gears are bearing very-high-cycle fatigue. Rolling contact fatigue is the main cause of the high-speed train wheels. However, the very-high-cycle fatigue of wheel steel under rolling contact loading has been rarely investigated. This project investigates the following scientific problems for the very-high-cycle fatigue of wheel steels by rolling contact fatigue tests and fatigue of serviced wheels. (1) The mechanism of crack initiation and early propagation for the very-high-cycle fatigue of wheel steels under rolling contact loading; (2) The microstructure evolution in the interior crack initiation region; (3) The effects of inclusion size and crack initiation location on the fatigue life. The aim of this project is to explore the essence of fatigue and fracture for wheel steels in very-high-cycle fatigue regime under rolling contact loading, clarify the microstructure evolution and formation mechanism of FGA, and construct a model involving the effect of inclusion size and location for fatigue life prediction in very-high-cycle fatigue under rolling contact loading in order to give a reference for fatigue life prediction and reliability evaluation of the train wheels.

随着高速铁路的快速发展，很多关键零部件包括车轮、车轴和齿轮等都承受超高周次的循环载荷；其中滚动接触疲劳是高铁车轮失效的主要形式，而在滚动接触载荷作用下车轮钢的超高周疲劳行为的研究还较少。本项目围绕滚动接触载荷下车轮钢的超高周疲劳行为，结合滚动接触疲劳实验和实际车轮的滚动接触疲劳两种实验手段，研究以下关键科学问题：（1）滚动接触载荷下车轮钢超高周疲劳裂纹萌生和初始扩展机制；（2）内部裂纹萌生区域的微结构演化特征；（3）夹杂尺寸和裂纹萌生位置对疲劳寿命的影响。预期目标：（1）揭示滚动接触载荷下车轮钢超高周疲劳裂纹萌生和初始扩展的基本特征和主要影响因素；（2）阐明滚动接触载荷下车轮钢内部裂纹萌生位置的微结构演化和FGA形成机理；（3）建立能反映滚动接触载荷特点的超高周疲劳寿命预测模型，为列车车轮疲劳寿命预测和可靠性评估提供参考。

系统开展了滚动接触载荷下铁路车轮超高周疲劳行为及寿命评估方法的研究。开展了ER8车轮钢超高周疲劳实验，车轮钢超高周疲劳裂纹萌生于试样内部夹杂物，观察到了典型的“鱼眼”特征，FGA形貌不明显。统计了近十年铁路车轮辋裂和剥离，结果表明辋裂是由内部（10-25 mm的深度处）夹杂物引起的疲劳破坏，破坏里程在十万公里，甚至百万公里以上，对应的疲劳寿命在10^7-10^9，属于超高周疲劳。车轮的服役载荷为滚动接触载荷，因此车轮辋裂和剥离的实质是滚动接触载荷下的超高周疲劳行为。辋裂萌生位置有一层等轴纳米晶特征形态的组织，为铁素体纳米晶，晶粒尺寸在20 nm左右，再往上方可以发现典型的珠光体形态的原始组织。经过超高周次的疲劳循环，微结构从原始的珠光体组织转变为铁素体纳米晶组织。车轮钢萌生位置没有发现纳米晶组织的存在，都是原始珠光体组织。利用ABAQUS软件分析了含夹杂物缺陷的轮轨接触应力分布，将轮轨接触应力引入FRANC3D软件进行裂纹扩展仿真。仿真结果与实际车轮辋裂结果较符合，证明了仿真计算的有效性。同时评估了夹杂物尺寸和位置对车轮疲劳寿命的影响。基于裂纹扩展曲线仿真结果，发展了车轮的滚动接触疲劳损伤容限分析和剩余寿命评估方法。