Crack detection in railway axles using continuous monitoring and periodic non-destructive inspection: experimental investigation on a freight wagon using a full-scale roller rig

This paper presents an experimental investigation aimed at assessing the possible use of axle-box acceleration measurements to identify the presence of a transverse crack in railway axles, detecting components of axle vibration occurring at frequencies that are integer multiples of the axle’s frequency of revolution (NxRev components). Experiments were carried out on an instrumented freight wagon equipped with two pre-cracked axles. Cracks were further propagated using a full-scale roller rig in order to reproduce conditions similar to the service ones, while ensuring safety. The size of the cracks during the tests was estimated by a dedicated non-destructive testing procedure based on magnetic particle testing and phased array ultrasonic testing, specifically designed to be simple and ergonomic so as to be suited for the use on the axles installed on the wagon. The results of the experiments confirm the feasibility of detecting a cracked axle by tracking the difference of the 3xRev components of the horizontal axle-box acceleration measured at the two sides of the axle, provided that the running speed of the wagon is at least 70 km/h. The minimum size of a detectable crack is in the order of 11% of the total cross section of the axle, which means that approximately 50% of the size that would lead to the final unstable phase of crack propagation preceding the failure of the axle.