One of the possible reasons for the failure of rails in railway tracks is the appearance of vertical cracks in the head, neck or bottom of the rail (see Fig. 1). Therefore, it is necessary to detect such defects at an early stage when the cracks are still of smaller dimensions. For vertical cracks, results of ultrasonic pulse-echo measurements are difficult to interpret due to mode conversions at the crack and rail surfaces, respectively. For normal incidence, not only the attenuation of the primary wavefront but also new echoes due to converted wave modes can be observed in the A-scan data.
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