考虑摩擦升温的铁路列车制动摩擦块高温磨损机制演变?

铁路列车制动摩擦块的高温磨损对列车制动安全影响显著，现有对于制动摩擦块高温磨损的研究一般通过环境温度控制来模拟制动界面高温条件，而在摩擦生热条件下对制动摩擦块高温磨损机理及演变规律的研究较少。在多模式制动性能试验台上进行摩擦拖曳制动试验，利用显微特征观测仪器、界面几何特征测量设备等，对制动摩擦块的高温磨损机理和演变进行分析探讨。结果表明，在摩擦生热条件下，当制动界面温度从室温上升至460℃时，摩擦块的主要磨损机制依次为磨粒磨损、氧化磨损和黏着磨损。当磨损机制以磨粒磨损为主时，摩擦块表面的缺陷数量多但尺寸小，摩擦因数与常温下接近；当氧化磨损占主导时，形成的氧化膜会提高耐磨性，摩擦块表面损伤较轻。此时，界面接触状态较好，摩擦因数较高，制动性能有所提高；当高温导致摩擦块材料发生软化和塑性流动时，摩擦块接触平台尺寸较大且极为平整，软化的材料充当润滑剂使摩擦因数下降、制动性能降低。同时，塑性流动会造成材料延展性能耗尽和表面材料撕裂，摩擦块表面严重的局部损伤导致接触界面状态较差，磨损机制以黏着磨损为主。在更接近于真实制动工况的条件下进行研究，揭示了摩擦升温过程中铁路列车制动摩擦块高温磨损机制的演变...

Evolution of High-temperature Wear Mechanism of Railway Train Brake Friction Block Considering Frictional Heat

With the opening of complex service lines, the high-temperature wear problem of brake friction blocks is increasing. Being an essential part of the train braking system, the high-temperature wear of a railway train brake friction block significantly impacts train braking safety. It is necessary to clarify the high-temperature wear mechanism of brake friction blocks. Typically, the ambient temperature is controlled with a heating device to increase the surface temperature of the friction block to the set temperature, and the tribological behavior test equipment is used to analyze the high-temperature wear behavior of the friction block. However, in the actual service process, the surface temperature of the friction block continues to increase during frictional heat generation. Although previous studies have reference significance for revealing the high-temperature wear mechanism of friction blocks, they cannot precisely reproduce the friction heating during the braking process. Some researchers have analyzed the high-temperature wear behavior of brake friction blocks at specific temperatures using friction braking tests; however, they did not analyze the evolution law of the high-temperature wear mechanism of friction blocks during friction braking. Therefore, it is necessary to investigate the high-temperature wear mechanism and evolution law of the brake friction block under the condition of friction heat generation. In this study, the friction drag braking test was performed on a multimode braking performance test bench. During the braking process, using a microphone, accelerometer, thermal imager, torque sensor, and other devices, the synchronous acquisition and storage of the noise signal, vibration signal, thermal signal, friction torque and other data were realized. Next, the microfeature observation instrument and interface geometry measurement equipment such as the optical microscope, scanning electron microscope, white-light interferometer, and interface profiler were used to analyze the high-temperature wear mechanism of the brake friction block based on the surface topography, friction coefficient, interface profile, contact platform, and debris. The results show that under the test conditions, the wear mechanism, friction, and wear behavior of brake friction blocks changed significantly with a continuous increase in brake interface temperature. When the brake interface temperature rises to approximately 180 °C, many surface defects appear on the friction block, but the sizes of the defects are tiny. Under this temperature condition, the coefficient of friction is close to that under the room-temperature condition, and the wear mechanism is mainly abrasive. As the braking process progresses and the brake interface temperature increases to approximately 330 °C, the oxidation layer formed on the brake friction block surface improves the wear resistance of the friction block. Surface oxidation causes less surface damage on the friction block, and the wear mechanism is mainly oxidation. At this time, the interface contact state improves, the coefficient of friction increases, and the braking performance is enhanced. When the brake interface temperature increases to approximately 460 °C, the wear mechanism of the friction block is mainly adhesive. The contact platform on the friction block surface is large and flat owing to the softening and plastic flow of the friction block material caused by high temperature. In this case, the plastic flow causes the material ductility to reach the maximum, tearing and peeling the material on the friction block surface. The frictional force causes severe local damage on the friction block surface, resulting in a weak contact interface between the brake disc and the friction block. Moreover, the softened material acts as a lubricant in the contact pair, reducing the coefficient of friction and the braking performance. This study reveals the evolution process of the high-temperature wear mechanism of railway train brake friction blocks during the friction heating process, and the test conditions are close to the actual braking conditions. The research results provide fundamental theoretical support for ensuring braking safety.