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在U71Mn钢轨截面上不同位置取9个带有燕尾状缺口的试件进行三点弯曲疲劳试验和超声波非线性检测,提取试件在不同疲劳加载循环次数下超声波的基波幅值和二次谐波幅值,据此计算钢轨疲劳过程的超声非线性系数,并用扫描电镜和金相显微镜观察对应试件表面的微观形貌,研究超声非线性系数与钢轨疲劳裂纹萌生和扩展的关系。结果表明:在钢轨疲劳过程中,超声非线性系数呈规律性变化;在试件疲劳的初期,超声非线性系数缓慢升高,当疲劳加载循环次数达到7万次以后超声非线性系数开始快速增长,对应的试件开始萌生裂纹,到9万次以后试件的裂纹开始生长,当疲劳加载循环次数达到11万次时超声非线性系数达到峰值,然后随着疲劳加载循环次数的继续增加,超声非线性系数开始呈降低趋势,并在13万次时裂纹已经生长为3mm长的宏观裂纹,这说明超声非线性系数对钢轨疲劳过程中裂纹的萌生和扩展的变化非常敏感,验证了超声非线性系数用于表征U71Mn钢轨疲劳损伤过程的有效性。
In the U71Mn rail section, nine specimens with dovetail notch were tested for three-point bending fatigue and ultrasonic non-linearity at different positions on the section of the rail. The amplitude of the fundamental wave and the second harmonic The nonlinear ultrasonic coefficient of the rail fatigue process was calculated. The microstructure of the specimen surface was observed by scanning electron microscope and metallographic microscope. The relationship between the nonlinear coefficient of ultrasonic wave and the initiation and propagation of fatigue crack was studied. The results show that during the fatigue process of rail, the nonlinear coefficient of ultrasound changes regularly. At the initial stage of fatigue, the nonlinear coefficient of ultrasonic increases slowly. When the number of fatigue loading cycles reaches 70,000, the nonlinear coefficient of ultrasonic begins to grow rapidly , The corresponding specimen began to crack, and the cracks began to grow after 90,000 shots. When the number of fatigue loading cycles reached 110,000, the nonlinear coefficient of ultrasonic wave peaked, and then the number of fatigue loading cycles continued to increase. Ultrasound The nonlinear coefficient started to decrease, and the crack grew into a 3mm long macrocrack at 130,000 times. This shows that the nonlinear coefficient of ultrasonic wave is very sensitive to the initiation and propagation of cracks in the fatigue of rail. The ultrasonic non-linearity The coefficients are used to characterize the fatigue damage process of the U71Mn rail.