3D CHARACTERIZATION OF SQUAT CRACK NETWORKS USING HIGH-RESOLUTION X-RAY RADIOGRAPHY

摘要

Rolling contact fatigue (RCF) damage is becoming more frequent with increased traffic, accelerations, and loading conditions in the railway industry. Defects which are characterized by a two-lobe darkened surface and a V-shaped surface-breaking crack are defined as squats. The origination and propagation of squats in railway rails is the topic of many recent studies; the associated crack networks develop with complicated geometry near the surface of rails, but can be difficult to detect using most non-destructive methods. The cracks can be examined with repeated metallographic sectioning, but the process is time-consuming and destructive. The aim of this study was to examine the potential of using high-resolution and high-energy X-ray imaging of rails in order to reduce time, as well as information and material loss. This first trial was performed on a Category B squat from a rail section taken from field. Combining the exposures from a range of angles using geometrical reconstruction, a 3D representation of the complex crack network is achieved. The latter was complemented with metallographic sectioning to determine the accuracy of prediction of the geometrical reconstruction. The 3D reconstruction showed accurate geometry in the medium depths, though the crack tips were not visible, due to limitations in radiography in terms of detecting tightly closed cracks.