Abstract: When the ultrasonic measurement of rail defects is carried out by the phased-array total focusing method (TFM), the accuracy of defect quantification is still not enough. For this purpose, the traditional distance amplitude correction (DAC) method is introduced into the TFM technique. Combining the sound field model, the system function and the flaw scattering model, an ultrasonic measurement model is established to predict the Full Matrix Capture signal set of the rail defects. Then, the TFM imaging results are obtained by the superposition of the delayed time domain data. By traversing the defect locations and sizes, a family of TFM-DAC mapping is constructed for a given ultrasonic phased array probe. The experimental results show that the quantification accuracy of rail defects with TFM-DAC mapping is better than 6%, while the quantification accuracy is as high as 13% when using traditional -6dB method. Further, the influences of inactive elements on the ultrasonic energy distribution of TFM and the quantification of rail defects are also revealed. By using the proposed method under the simulated conditions that a quarter of elements is broken, the one-to-one correspondence between the inactive elements and the TFM-DAC mapping is explored. The quantification accuracy of rail defects is not significantly reduced. In short, the present method is an important guiding for extending the economic service life of the phased array transducer.

Key words: ultrasonic phased array, rail detection, distance amplitude correction, total focusing method, defect quantification