极端气温下铁路轨道扣件系统疲劳劣化及其演变失效机制研究

为了指导制定极端气温下铁路轨道扣件系统的疲劳失效评判标准及其养护维修规范，首先研究建立反映弹条几何/材料非线性、弹性垫板材料非线性以及各部件间接触非线性的轨道扣件系统三维非线性有限元模型，计算分析列车正常疲劳荷载或异常高频冲击荷载作用下轨道扣件系统弹性部件边界的位移、速度与加速度荷载模式；然后通过创新弹条疲劳试验方法，借鉴断裂动力学理论以及拓展应用温频等效原理，研究极端气温与列车荷载长期作用下扣件弹条疲劳裂纹的萌生、扩展机理以及扣件弹性垫板力学服役性能的热氧+疲劳荷载耦合老化机制；最后运用反映弹性部件疲劳性能演变的扣件系统三维非线性有限元模型以及极端气温与列车荷载长期作用下轨道扣件系统的室内组装疲劳试验和现场状态监测结果，探究铁路轨道扣件系统内弹条、弹性垫板等弹性部件间及其与非弹性部件间非线性耦合作用的长期循环反馈机制，继而研究建立极端气温下铁路轨道扣件系统疲劳寿命的科学预测方法。

In order to guide the formulation of the fatigue failure evaluation criteria and maintenance specifications for the railway track fastening systems under extreme temperatures, there are three studies need to be done. At first, it is necessary to establish a three-dimensional nonlinear finite element model of the track fastening systems, which model can reflect the geometric/material nonlinearity of the fastening clip, the material nonlinearity of the elastic pad and the contact nonlinearity among the various components. This model will be used to calculate and analyze the load modes of the displacements, velocities and accelerations on the boundaries of the elastic components in a track fastening system under the train-induced normal fatigue loads or the train-induced abnormal high frequency impact loads. Secondly, based on the innovative test methods for the fatigue fracture of fastening clip, the fracture dynamics theory and the Time-Temperature Superposition (TTS), the fatigue crack initiation and propagation mechanisms of the fastening clip under the long-term coupling effect between extreme temperatures and railway train loads are investigated, and the comprehensive aging mechanism of the thermal oxidation and fatigue loads on the mechanical serviceability of the elastic pad is also discussed. Finally, by using the three-dimensional nonlinear finite element model of the track fastening systems, which model can further reflect the fatigue evolution of the elastic parts of the track fastening systems, combined with the indoor fatigue test and field service situation measurement of the track fastening systems under extreme temperatures and long-term train fatigue loads, the long-term cyclic feedback mechanism of the nonlinear coupling interaction between the elastic parts and the other non-elastic parts in a track fastening system is explored, and then the scientific prediction method for the fatigue life of the track fastening systems under extreme temperatures is established.