基于同步挤压小波和脉冲压缩的钢轨踏面裂纹电磁超声表面波检测方法研究

钢轨踏面上的疲劳裂纹严重影响着列车行车安全。 针对如何快速有效地检测出踏面斜裂纹的问题,本文提出了一种快速检测钢轨踏面裂纹的方法。 首先分别建立了含高斯白噪声、正弦信号加高斯白噪声干扰的数学模型,分析了编码脉冲压缩、同步挤压小波变换和先同步挤压小波变换后脉冲压缩共 3 种信号处理方法的噪音抑制效果。 其次,为了验证上述方法对噪音的抑制能力,使用激励频率为 1 MHz 的表面波电磁超声换能器对含裂纹的钢轨踏面进行检测。 最后,以检测得到裂纹的超声回波为研究对象,比较了希尔伯特黄方法处理单一频率脉冲对应的超声回波信号和先同步挤压后脉冲压缩方法对应的降噪能力和超声成像效果。 实验结果表明:本文所提方法可以获得钢轨踏面裂纹的位置信息及其数量。 希尔伯特黄变换在处理无同步平均的原始超声回波时,由于回波信噪比低,经验模态分解(EMD)失效。 在以巴克码为激励信号且无同步平均采集的条件下,先进行同步挤压小波变换后脉冲压缩处理,得到的超声回波信噪比相较于只采用相位编码脉冲压缩提高了 6. 82 dB,相比于只做同步挤压小波变换提高了 11. 02 dB,能明显提升检测速度和 B 扫图像分辨率。

Research on the electromagnetic ultrasonic surface wave detection method of rail tread crack based on synchrosqueezed wavelet transform and pulse compression

Fatigue cracks on the rail tread seriously affect the safety of trains. To address the problem that detects rail tread cracksquickly and effectively, a method for rapid detection of rail tread cracks is proposed in this article. Firstly, the mathematical models withGaussian white noise and sinusoidal signal plus Gaussian white noise interference are formulated respectively. The noise suppressioneffectiveness of three signal processing methods are analyzed, including the coded pulse compression, the synchrosqueezed wavelettransform and the pulse compression after synchrosqueezed wavelet transform method. Secondly, to evaluate the noise suppression abilityof the above methods, the surface wave electromagnetic ultrasonic transducer with excitation frequency of 1 MHz is used to detect the railtread with cracks. Finally, the ultrasonic echo of the detected crack is taken as the research object. The noise reduction ability andultrasonic imaging effect of the Hilbert Huang method for processing the ultrasonic echo signal corresponding to a single frequency pulseand the method of synchrosqueezed wavelet transform followed by pulse compression are compared. Results show that the proposedmethod can obtain the location and number of cracks on the rail tread. When Hilbert Huang transform is used to process the originalultrasonic echo with no synchronous average, the signal-to-noise ratio of the echo is low, which causes the failure of the empirical modedecomposition ( EMD). Under the condition that Barker code is used as the excitation signal and there is no synchronous average acquisition, the signal-to-noise ratio of ultrasonic echo obtained by using the pulse compression after synchrosqueezed wavelet transformmethod is 6. 82 dB higher than that using only phase coding pulse compression. It is 11. 02 dB higher than that using only synchrosqueezed wavelet transform, which can significantly improve the detection speed and B-scan image definition.