Study on surface waves for detection of fatigue cracks in railway joint bars.

• Ultrasonic surface wave was explored to detect fatigue cracks located in the head of the joint bars (usually not accessible visually in tracks). • Laboratory testing has identified parameters potentially enabling detection of fatigue cracks in visually inaccessible areas of joint bar heads. • The 0.5 MHz transducer was most suitable to detect inaccessible fatigue cracks out of other transducers typically used in revenue service. • A 25.4 mm diameter 0.5 MHz transducer positioned at a 30 ° yaw axis angle and offset at 38.1 mm to the side provided best SNR for crack detections. The current method of inspecting railway joint bars involves the use of high-resolution cameras to detect fatigue cracks that have undergone significant cracking exposed to the surface. The novelty of the work presented in this paper discusses the development and application of non-contact ultrasonic surface wave approach to detect and characterize near-surface fatigue cracks in the head of the railway joint bars which is not usually accessible for inspection. Simulated cracks were implanted in the head of the two different used joint bars to assess the capabilities of the ultrasonic nondestructive evaluation (NDE) surface wave approach. One of the joint bars was implanted with 3.175 mm and 6.35 mm cracks in length, while the other joint bar was implanted with 12.7 mm and 25.4 mm cracks in length. Despite the complex geometry of railway joint bars, the laboratory proof-of-concept testing conducted in an immersion water tank demonstrated that the developed non-contact surface wave approach successfully detected implanted cracks in both joint bars. The results obtained from the study indicate that a 0.5 MHz ultrasonic transducer provided the best sensitivity for detecting implanted cracks compared to 1 MHz and 2.25 MHz transducers. Similarly, test results obtained with a 0.5 MHz ultrasonic transducer, launching a surface wave from an accessible area to an inaccessible area of the joint bar (where the implanted cracks were located) yielded a significantly higher signal-to-noise ratio (SNR) than the 1 MHz and 2.25 MHz transducer. [ABSTRACT FROM AUTHOR]