Method for Detecting Defects in Switch Rails Based on the Wavelet Baseline

Switch rail is an important basic component of rail transportation. Due to its variable cross section structure, there are many guided wave modes that can propagate inside it. When the ultrasonic guided wave is used to detect the defect of switch rail, the defect echo is often superimposed with complex background signal, which is difficult to extract. To solve the problem that the time-domain baseline method needs complex temperature compensation algorithm and is difficult to be applied in engineering, this article explores a new method from the frequency domain. The Fourier transform is applied to the waveguide signal and the FFT result of a waveguide signal from a nondefective switch rail is selected as the baseline. The difference of the FFT result between the waveguide signal and the baseline is calculated by the algorithm designed, being defined as a frequency-domain operator. The results show that the frequency-domain baseline method has a comprehensive identification rate of 99.89% and that no temperature compensation is required for indoor switch rail detection. Based on this, this article proposes the wavelet baseline method that integrates time-domain and frequency-domain analysis. The 3-D waveform data of the guided wave is transformed by wavelet, the difference between the data to be recognized and the baseline data is calculated based on the corresponding segments by the algorithm designed, and the frequency-time operator is obtained. For indoor datasets, the comprehensive detection rate of the wavelet baseline method is 99.93%, and the defect discrimination is better than that of the frequency-domain baseline method. For outdoor test data collected within 28 days, the comprehensive detection rate of the wavelet baseline method is 99.2%. The defect detection experiment of the switch rail on the actual line with the accessory structure is also carried out. The results show that the wavelet baseline method can effectively identify the defects of the switch rail in service. The wavelet baseline method proposed in this article can identify the defects of the switch rail effectively by dividing the temperature interval without complicated temperature compensation algorithm, and has practical value in engineering and application.