TourTourSurface fatigue / fatigue fracture
Rail track failure analysis >>

A shallow angle crack initiated at the surface is turned down into the rail,
a serious failure mode.

From Hertz theory it is known that with pure rolling the crack is subsurface initiated and propagates to the surface, resulting in a shell or spall.

In the case of rolling with traction (>1/9) the crack is surface initiated (Chapter 2) and may propagate to the surface or down into the rail