Based on the endeavors have been made to reduce the wear rate of the railway wheels surfaces, and increase in the axle loads and the velocity of the trains, rolling contact fatigue of the railway wheels is nowadays a considerable damage with regard to the railway wheels. The initiated cracks in the wheels are classified into surface and subsurface ones. The former are usually removed by wear, while the latter propagate gradually until reaching the critical crack length and then suddenly bring about dangerous fractures. So, in any maintenance process of a railway system, it is essential to have the critical crack length as a vital tool to determine the possibility of the critical condition occurrence in the case of identified cracks in wheels. The critical crack length is a residential value and should be determined for any railway systems. So, by using FEM, this paper models an Iranian Railways wheel having the diameter of 920mm, made of R7T material which has a subsurface crack. The wheel is in contact with UIC60 rail. After analysis of this model, rang of stress intensity factor of the crack has been calculated for the different rotation angles. Finally, the critical length of a subsurface crack in conformity with Iranian Railways has been determined based on the fracture mechanics and some approximate relations about mechanical properties. Results show that because of geometrical limitations of the wheel, a subsurface crack can cause the wheel fracture before reaching the critical length.

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