Ultrasonic Inspection of Axle Flaws at Fitting Seats in Consideration of Probability of Detection (POD)

摘要

In the ultrasonic inspection of railway axles, the sensitivity is usually adjusted using a model wheelset where some artificial flaws are machined. The flaw echo height can be associated with its size by the linear regression. However, the echo heights essentially have some dispersion and it would become wider for the flaws in the fitting seats where a wheel or a gear is fitted. In this study, the relation between the flaw echo height and the reflection area of flaws was obtained for the hollow axles with some artificial flaws on their respective surfaces. The relation for the flaws in the axle body was compared with the one for the flaws in the wheel seat with the help of the probability of detection (POD) curve. Even though the detection threshold with the probability of 50% was set for a flaw having an almost identical area in each case, the detectable area of a flaw with the probability of 90% at a lower confidence limit of 95% in the wheel seat was more than twice larger than that in the axle body. It implies that the flaw detection threshold in the fitting seats should be lowered additionally to keep sufficient confidence.