Contribution of railway dynamics codes to the understanding of the metallurgical behavior of the rail tread

Abstract

The contact fatigue of rail treads affects railway networks exploiting high-speed straight lines and has been described in many articles (P.E. Bold et al., Wear, 144 (1990) 307–317; R.Y. Deroche et al., Rail Quality and Maintenance for Modern Railway Operation Conf, Delft, June 1992; A.F. Bower and K.L. Johnson, Wear, 144 1–18). The defect may be seen, at an advanced stage of development, as a subsiding of the rail tread due to a slightly inclined cracking. This leads to the formation of a characteristic black patch called a squat that can progress as a crack into the rail until breaking it completely. The origin of the defect is difficult to analyze. It has been believed for a long time that tangential stresses, associated with traction forces of locomotives, were of importance. However, this hypothesis, that should predict a higher probability of these defects on low-speed lines having heavy trains, does not fit with field experience that they develop mainly on high-speed lines and with inclined cracking. After having described the superficial rail tread residual stresses, this paper shows that it is possible to explain them using rail tread loading cases due to the effect of the hunting of high-speed locomotives, with or without traction forces. Loading cases are calculated with the help of the simulation VOCO codes developed by the INRETS.