Determination of Threshold and Critical Dubsurface Crack Length in the Wheel of Iranian Railway Systems

In the last two decades, decreasing wear rate beside of increasing axel loads and trains velocities have changed the main failure of steel wheels from wear to rolling contact fatigue (RCF). RCF causes surface and subsurface cracks. The former usually disappeared contrasting with wear while the latter propagates and brings about deeper and more dangerous fractures. In any maintenance process of railway systems, having criteria of threshold and critical crack length is a vital tool to determine possibility of propagation and critical condition of identified cracks in wheels. In this paper, stress intensity factor range of a subsurface crack has been calculated by FEM analysis of monobloc R7T wheel in contact with UIC60 rail. Then, threshold and critical length of subsurface crack in the wheel of Iranian railway system have been determined based on fracture mechanics and some approximate relations about mechanical properties. Findings show that a subsurface crack longer than about 3 mm can gradually propagates and before reaching the critical length can make the wheel fracture because of geometrical limitation of the wheel.