Automated Detection of Cracked Railway Axle Journals Using an Ultrasonic Phased Array Technique

Railway vehicle axles experience fatigue behavior. This has become a critical issue considering both the increased loads and speeds of railway vehicles. The failure of one axle has the potential to cause derailment of the entire train. Train derailment can cause danger to the public, threaten lives, and cost thousands of dollars in repair and rehabilitation. A critical area is the axle journal. Inspecting axle journals is difficult due to limited accessibility, as the journal and nearby areas are covered by the bearing, bearing cap, and wheel. The main challenge of this research is to overcome the limited accessibility using ultrasonic techniques.

Three main railway axle journal inspection concepts have been developed in this research: 1) automated detection system of a cracked axle journal using the ultrasonic phased array technique, 2) detection of a cracked axle journal using a chain scanner, and 3) cracked axle journal detection using surface waves. An ultrasonic phased array system has a much higher probability of detection (POD) and will provide a much more rapid inspection when compared to conventional ultrasonic transducers. Surface wave inspection proves that it can propagate along the complex geometry of the railway axle journal. Support vector machine (SVM) and the developed algorithm successfully distinguished between a cracked axle and an uncracked axle. Signal processing with a threshold classifier was developed to provide a faster computation time.

Three different air-coupled experiments are demonstrated: 1) the line-source air-coupled ultrasonic array sensors in through-transmission mode, 2) the point-source air-coupled ultrasonic generation using Rayleigh waves, and 3) the laser array detector on a steel plate. A complete air-coupled ultrasonic system is achieved with the air-coupled 20-array ultrasonic line source and point source with microphone sensor as receiver. The best results can be obtained with an excitation frequency range of 50 to 100 kHz. The generated ultrasonic waves successfully penetrated the aluminum sheet, the low-density polyethylene (LDPE) plate, and the concrete mortar using the through-transmission technique. The one-side non-contact crack detection is demonstrated using a Rayleigh wave. It successfully distinguishes between cracked and uncracked regions using the time-of-flight technique. A complete air-coupled ultrasonic system is developed for various materials in this research.