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Visualization and modelling to understand rail rolling contact fatigue cracks in three dimensions

Lookup NU author(s): Dr David Fletcher, Dr Francis Franklin

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Abstract

The article presents an extensive survey of experimental data on rolling contact fatigue (RCF) crack shape and propagation characteristics in rails removed from service, where such cracks are angled to the rail axis. The data include re-analysis of previously published experimental data to extract crack shape information and new experimental work on crack shapes at different stages in the early RCF life. Periods from initiation (ratcheted 'flake cracks') have been considered through very early growth to the limit of one prior austenite (PA) grain and on to rail-head visual cracks. Techniques included multi-sectioning through single cracks and crack zones, on used rail and test discs, to build up real three-dimensional (3D) data on crack shapes and propagation characteristics. This data have been compared with the UK rail system guidance charts relating to visual crack length and respective vertical depth; all data fell within the indicated guidance zones. The configuration of such angled cracks, typically found in curves, so aligned due to the vector of both lateral and longitudinal traction, rather than just axially, was identified as an important case for modelling. A fracture mechanics-based model has been developed to predict modes I and II stress intensity factors for such cracks covering multiple PA grains. An important geometry effect is revealed by which a contact approaching a crack angled to the rail axis is effectively 'offset' from the approach direction considered in 2D models, thereby resulting in lower predicted peak stress intensity factor values, compared with 2D, for the prediction of crack growth rates.


Publication metadata

Author(s): Garnham JE, Fletcher DI, Davis CL, Franklin FJ

Publication type: Article

Publication status: Published

Journal: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit

Year: 2011

Volume: 225

Issue: F2

Pages: 165-178

Print publication date: 01/01/2011

ISSN (print): 0954-4097

ISSN (electronic): 2041-3017

Publisher: Sage

URL: http://dx.doi.org/10.1177/2041301710JRRT414

DOI: 10.1177/2041301710JRRT414


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