3D characterization of rolling contact fatigue crack networks

Abstract

a b s t r a c tRolling 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 nondestructive 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 Â 10 Â 30 mm 3 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.

Crack formation within a Hadfield manganese steel crossing nose

“…A discontinuous dynamic recrystallized layer was observed on the worn surface of a manganese crossing in one study, whereas the aggregation of vacancy clusters due to deformation leading to cracking has been reported in another study. Previous works [9][10][11][12] on crack formation in rail steels have almost exclusively been done on normal pearlitic steel grades. Here it is found that the microstructure changes during service due to plastic deformation, which is important for crack propagation as it influences the crack path.…”

“…Examples include Garnham et al [12] making schematic representations of the crack geometries in pearlitic rails and Schilke et al [9] studying the crack growth on normal pearlitic grade R350HT rail steel. A non-destructive 3D X-ray computerized tomography technique was used by Jessop et al [10] and Zhou et al [11] for visualizing crack networks, where the crack and its side branches could be visualized with high resolution in 3D in pearlitic grade rail steels.…”

Investigation of the Effect of Magnification, Accelerating Voltage, and Working Distance on the 3D Digital Reconstruction Techniques

“…The development of the scanning electron microscope (SEM) [ 1 ] and the 3D digital reconstruction techniques [ 2 – 4 ] along with the development of image processing methods, hardware and software, can significantly help in a broad range of applications such as investigation of fracture surfaces [ 5 ], surface engineering [ 6 ], 3D printing [ 7 ], and biological researches [ 8 ]. To reconstruct a 3D digital image from multiple SEM images, correct types of features should be chosen on the 2D images [ 9 ].…”

2D and 3D characterization of rolling contact fatigue cracks in manganese steel wing rails from a crossing

“…Although swing nose crossings with less impact levels can be used for heavy haul and high speed systems, in recent years manganese steel has been the preferred choice for fixed crossings because of superior mechanical properties. Most studies on deformation and cracks in rail steels are done for pearlitic steel taken from normal tracks [2][3][4][5][6][7][8]. Not much work has been published in the literature on the damage and degradation behaviour of manganese steel crossings, in contrast to the use of manganese steel in abrasive wear applications such as rock crushing equipment.…”