Journal article
3D characterization of rolling contact fatigue crack networks
Chalmers University of Technology1
Department of Wind Energy, Technical University of Denmark2
Materials science and characterization, Department of Wind Energy, Technical University of Denmark3
Villum Center for Advanced Structural and Material Testing, Centers, Technical University of Denmark4
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 and distinguish from normally existing head checks in their early stages, using in-field non-destructive detection techniques.
After cutting out damaged sections of rail, there are a number of options to characterize the damage. The aim of this study was to evaluate different methods to geometrically describe squat crack networks; through X-ray radiography complemented with geometrical reconstruction, metallography, X-ray tomography, and topography measurements.
The experiments were performed on squats from rail sections taken from the field. In the first method, high-resolution and high-energy X-ray images exposed through the entire rail head from a range of angles were combined using a semi-automated image analysis method for geometrical reconstruction, and a 3D representation of the complex crack network was achieved.
This was compared with measurements on cross-sections after repeated metallographic sectioning to determine the accuracy of prediction of the geometrical reconstruction. A second squat was investigated by X-ray tomography after extraction of a section of the rail head. A third squat was opened by careful cutting, which gave full access to the crack faces, and the topography was measured by stylus profilometry.
The high-energy X-ray, 3D reconstruction method showed accurate main crack geometry at medium depths; the advantage of the method being that it potentially could be developed for non-destructive testing in field. However significant drawbacks exist due to limitations in radiography in terms of detecting tightly closed cracks in very thick components.
This includes the inability to detect the crack tips which is an important factor in determining the risks associated to a specific crack. Metallographic investigation of the cracks gave good interpretation of crack geometry along the sections examined, and gave the possibility to study microstructure and plastic deformation adjacent to the crack face.
However this time-consuming method requires destruction of the specimen investigated. The X-ray tomography revealed the 3D crack network including side branches in a 10×10×30mm3 sample, and provided topographic information without completely opening the squat. Topography measurements acquired by stylus profilometry provided an accurate description of the entire main crack surface texture, including features such as surface ridges and beach marks.
Language: | English |
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Year: | 2016 |
Pages: | 392-400 |
ISSN: | 18732577 and 00431648 |
Types: | Journal article |
DOI: | 10.1016/j.wear.2016.06.027 |
ORCIDs: | Fæster, Søren and Danielsen, Hilmar Kjartansson |
Automated image analysis Complex networks Condensed Matter Physics Crack detection Crack tips Cracks Electron microscopy Fatigue damage Fatigue of materials Friction Geometrical reconstruction Geometry Image reconstruction Imaging systems Materials Chemistry Mechanics of Materials Metallography Microstructure Non destructive testing Nondestructive detection Nondestructive examination Optical microscopy Profilometry Radiography Railroads Rails Rolling contact fatigue Rolling contact fatigue cracks Surface defects Surfaces and Interfaces Surfaces, Coatings and Films Tomography Topographic information Topography X ray radiography X-ray tomography