The Growing Of Micro-Crack On Wheel/Rail Contact Surface With Surface Micro-Roughness

With the increase of railway freight and train speed, rolling contact fatigue has become one of the most prominent problems which constrain railway technology development, especially in the high speed heavy lines. It not only greatly increases the railway operating costs, but also directly endangers traffic safety. Therefore, the researches on the surface micro-crack propagation behavior under micro-roughness can contribute to correctly judge the failure types and the failure causes of rail, accurately estimate the rail contact fatigue crack propagation life. It has important practical significance for maintaining the security of high-speed rail service, promoting rail quality, extending rail service life and saving the cost of railway operation.In this thesis, the researches on the surface micro-crack propagation behavior under micro-roughness were discussed. Two dimensional finite element model of wheel-rail contact surface micro-crack under micro-roughness was established by using finite element program ANSYS. Stress and stress intensity factors of rail surface micro-crack tips at different length and locations with or without a liquid medium were given by calculations. The fatigue micro-crack propagation life of two cases was compared. The main conclusions were:1. In the wheel rolling process, the micro-cracks of rail with surface micro-roughness and the contact surface without liquid medium only opened at the edge of the contact patterns. In the other locations, the opening deformation didn't appear. The micro-cracks were closed. And the largest'equivalent stress intensity factor of type I'K1* was much smaller than the rail material fracture toughness. It was described that rail surface micro-cracks would not extend immediately in this case.2. In the wheel rolling process, the micro-cracks of rail with surface micro-roughness and the surface with liquid medium oprned in the whole contact patterns. The micro-crack type was I-II mixed mode crack. The maximum 'equivalent stress intensity factor of type I K1* with liquid medium was much bigger than the maximum' equivalent stress intensity factor of type I'K1* without liquid medium, about 4.3 times.3. The crack propagation life of the rail with surface micro-roughness and with liquid medium was much smaller than the crack propagation life of the rail with surface micro-roughness and without liquid medium. It explained that in order to reduce the side wear between wheel and rail, when the rail surface was coated with lubricant, the surface cracking phenomenon in the curve rails was much more serious than the linear rails.