Metallurgical study of rail squats

A rail squat is a type of rolling contact fatigue defect of growing concern. A crack grows below the rail surface, leading to a depression in the rail as material above the crack flows plastically. Studies of squat cracks using optical and electron microscopy will be described. One feature often observed is a “white etching layer” on the surface of the rail. The name reflects the fact that this layer refuses to reveal its crystalline microstructure when etched with nitric acid, and indicates it has a nanocrystalline nature. It is a thin brittle layer (eg 30 microns thick) formed by severe local heating, and can occur with transient wheel slip. The presence of this layer can initiate a crack, which can then grow subsurface both in the direction of traffic and against the direction of traffic. The appearance of the crack surface will be discussed. There are regions that show evidence of cycles of faster or slower crack growth, and other smooth regions, that are featureless even when seen through a microscope. These give clues as to how the crack grew, whether in shear or in tension due to water getting in the crack.

Media Info

  • Pagination: 8p.
  • Monograph Title: Rejuvenation and renaissance: CORE 2010: conference on railway engineering, 12-15 September 2010, Wellington, New Zealand

Subject/Index Terms

Filing Info

  • Accession Number: 01517082
  • Record Type: Publication
  • Source Agency: ARRB
  • Files: ATRI
  • Created Date: Mar 4 2014 8:07PM