On the genesis of squat-type defects on rails

On the genesis of squat-type defects on rails: Toward a unified explanation

Steenbergen, M.J.M.M. (TU Delft Mechanics and Physics of Structures)

2021

Different origination theories for squat-type rail defects are examined and confronted with experimental evidence. Based on the morphology of the three-dimensional defect crack pattern, with a leading crack directivity governed by the tangential stress history, it is shown that theories assuming dynamic wheel-rail interaction as a direct initiation mechanism of the double-lobed defect violate the causality principle. Rail surface anomalies of three categories increase the tangential stress exposure and thus the risk of defect development: pertaining to the material properties, contact geometry (including both the global scale, involving the dynamic stress level transmitted by the contact area, and the local scale, involving transient stress redistribution within this area), and contact stiffness. Both detection measures focusing on geometrical surface deviations giving rise to dynamic wheel-rail interaction (such as axle-box acceleration measurements) and the idea of a critical diameter for such imperfections are inadequate. Instead, and apart from the surface geometry, steel micro-cleanliness and chemical composition, phase transformation mechanisms of surface material (due to operational conditions or treatment by grinding or milling) and welding deserve attention. Fluid entrapment remains a potentially contributing factor in early growth, while crack face oxidation and corresponding volumetric expansion may contribute at any stage after initiation.

Axle box acceleration
Rail defect
Rolling contact fatigue
Squat
Surface cracking

http://resolver.tudelft.nl/uuid:5b806740-559a-4f6c-84d0-9876557e3fde

https://doi.org/10.1016/j.wear.2021.203906

0043-1648

Wear, 478-479, 478-479

Institutional Repository

journal article

© 2021 M.J.M.M. Steenbergen