A high manganese steel rail is currently used at crossing points for local lines and the Shinkansen (bullet train) in Japan. These rails contain no less than 11 to 14% of manganese; however, common steel rails contain only about 1%. One of the advantages of using high manganese rails is that they have high damage tolerance to fatigue cracks and so a longer life span. Usually, rails are regularly inspected by ultrasonic testing (UT). However, the UT isn’t applied to high manganese steel rails because many ultrasonic scatterings occur in high manganese steel rails due to their larger crystal grains and casting defects. As an alternative to UT, visual or penetrant testing (VT or PT) is carried out, though this requires rails to be removed from their anchor points and turned over manually. This process is expensive financially and time-wise. This study aims to develop ultrasonic testing to inspect fatigue cracks without removing the rails. First, the difficulties for ultrasonic inspection by the conventional method are investigated. The difficulties are then solved in two ways. One is pulse compression techniques by frequency modulation and the other is a combined method of aperture synthesis and wavelet transformation.

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