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Analyzing the mechanisms of fatigue crack initiation and propagation in CRH EMU brake discs

机译：分析CRH动车组制动盘疲劳裂纹萌生与扩展的机理

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摘要

A significant number of high-speed electric multiple units' (EMU) brake discs, manufactured from forged steel, showed thermal cracks during work and NDT. There exist three kinds of cracks on the friction surface; namely, the crackle, radial crack and circumferential crack. Macro-morphologies of the friction surface indicate that the cracks appeared in the interior and edges of the hotspots. Crack growth methods include the single crack propagation and multiple crack connectivity. A finite element analysis (FEA) was performed to determine temperature and stress distribution in the brake disc as well as to estimate stress distribution during braking. Simulation results indicate more significant residual, circumferential tensile stress on the external friction surface after emergency braking. The maximum residual circumferential tensile stress is 200 MPa after 300 km/h emergency braking. In addition, there is only the circumferential compressive stress on a section which is a certain distance from the exterior of the friction surface, and the distance depends on braking conditions. Therefore, not taking into account thickness reduction of the friction surface due to wear, it can be concluded that when the cracks run along the thickness direction to the specified distance, they will cease to run along this direction and begin propagating mainly in the direction of the radius. In addition, based on the simulation results, a measure was presented to prevent and inhibit the crack propagation.
机译：大量由锻钢制成的高速电动多单元（EMU）制动盘在工作和无损检测中均显示出热裂纹。摩擦面上存在三种裂纹。即裂纹，径向裂纹和周向裂纹。摩擦表面的宏观形态表明裂纹出现在热点的内部和边缘。裂纹扩展方法包括单裂纹扩展和多裂纹连通性。进行了有限元分析（FEA），以确定制动盘中的温度和应力分布，以及估算制动过程中的应力分布。仿真结果表明，紧急制动后，外摩擦面上的残余，周向拉伸应力更大。 300 km / h紧急制动后，最大残余周向拉应力为200 MPa。另外，在离摩擦表面的外部一定距离的部分上仅存在圆周压缩应力，并且该距离取决于制动条件。因此，不考虑由于磨损引起的摩擦面厚度的减小，可以得出这样的结论：当裂纹沿厚度方向延伸到指定距离时，它们将停止沿该方向延伸，并开始主要沿裂纹方向传播。半径。另外，基于仿真结果，提出了防止和抑制裂纹扩展的措施。

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