Early stages of rail squat formation and the role of a white etching layer

Pal, Sarvesh, Daniel, William J. T. and Farjoo, Mohammadali (2013) Early stages of rail squat formation and the role of a white etching layer. International Journal of Fatigue, 52 144-156. doi:10.1016/j.ijfatigue.2013.02.016

Author Pal, Sarvesh
Daniel, William J. T.
Farjoo, Mohammadali
Title Early stages of rail squat formation and the role of a white etching layer
Journal name International Journal of Fatigue   Check publisher's open access policy
ISSN 0142-1123
Publication date 2013-07
Sub-type Article (original research)
DOI 10.1016/j.ijfatigue.2013.02.016
Volume 52
Start page 144
End page 156
Total pages 13
Place of publication London, United Kingdom
Publisher Elsevier
Collection year 2014
Language eng
Abstract A squat is a rolling contact fatigue crack below the surface of a rail that leads to a depression in the surface. Squats were thought to initiate by ratcheting (cyclic plastic shear deformation of the surface layer). However, the rail is often found to have a martensitic hard layer which refuses to etch (a white etching layer) on the surface, indicating a thermal crack initiation process. Grassie et al. [1] has suggested these cracks should be given a different name "studs" to distinguish their thermal origin. This paper describes detailed observations of cracks at a site where no white etching layer was evident. Hence these cracks can confidently be labelled as squats. Three stages of squat formation have been identified. Firstly, there is an early stage of crack initiation due to a white etching layer or ratcheting, and then growth of a subsurface crack leading to formation of a squat, caused by entrapped water inside the crack, and finally spalling off of a piece of rail surface. Rails with squat defects in different stages were removed from the site, investigated and inspected visually, ultrasonically, optically and by using electron microscopy to find the main cause of crack initiation and squat formation Microscopic observations revealed primary, secondary and tertiary cracks in the transverse section of rails, and differences in crack surface appearance. Primary cracks initiated at an angle of 10-15° with respect to the rail surface and then turned down at an angle of 50° with respect to the rail surface. Secondary cracks initiated at an angle of 160° with respect to the rail surface and further bifurcated in tertiary cracks. Microhardness of the damaged rail surface was higher than that of the adjacent rail matrix but was not comparable with that of a white etching layer or martensitic structure.
Keyword Rolling contact fatigue
Contact mechanics
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mechanical & Mining Engineering Publications
Official 2014 Collection
Version Filter Type
Citation counts: TR Web of Science Citation Count  Cited 6 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 9 times in Scopus Article | Citations
Google Scholar Search Google Scholar
Created: Sun, 16 Jun 2013, 00:22:10 EST by System User on behalf of School of Mechanical and Mining Engineering