Using comprehensive probability of detection curves to support determination of inspection intervals of railway axles

Deutsche Bahn periodically inspects hollow railway axles for fatigue cracks on the outer surface with mechanized ultrasonic inspection systems. According to the current standard for the inspection of railway axles, the capability of the inspection system to detect these cracks has to be demonstrated on the saw-cut type artificial defects. However, the geometry and the ultrasonic response of the real cracks that can occur on the outer surface of the axle are different from the saw-cut. Furthermore, it is demonstrated that the position and the orientation of the cracks are also important factors that influence the crack detectability. It is proposed to evaluate the influence of all factors on the detection of the cracks using the multi-parameter reliability model. The model uses numerical simulation and experiments to comprehensively address the influence of several factors on the probability of detection.