Experimental technique to evaluate rolling contact fatigue in railroad wheels

The process of surface damage in railroad wheels is a very complex phenomenon. Contact fatigue plays a fundamental role in the damage process. Fracture due to repeated loading is known as fatigue. In the case of railroad wheels the actual fracture process is quite different from the conventional idea of fracture in a bearing load structural component. The cracks that are generated by contact fatigue are not the source of actual wheels cracking but lead to the damaging phenomenon of shelling. Shelling implies the separations of chunks of material from the surface that force the removal of the wheel because it is no longer viable as a rolling surface. The shelling of the surface is a mixed cause event. Cracks are developed in the wheel by rolling fatigue with friction, these cracks penetrate to a certain depth. To cause shelling it is necessary to have a fluid in the contact area that will penetrate in the fatigue cracks and will cause a crack propagation leading finally to material separation of a portion of the wheels surface. A basic starting point to analyse this phenomenon is to study the crack development in the surface contact and to evaluate the behavior of different types of steels that can be used in the manufacture of wheels. The present paper provides an experimental process for material fatigue evaluation based on the possibility of simulating in the laboratory conditions that can be scaled to the actual railroad conditions, thus providing a realistic evaluation of the contact fatigue life of different steels.