Formation of rail contact fatigue damage

- Jun 23, 2017-

The formation of contact fatigue damage can be divided into three stages: the first stage is the change of rail tread profile, such as the uneven rail tread, the weld seam appears saddle wear, these irregularities will increase the impact of the wheel on the rail; The second stage is the destruction of metal on the surface of the rail head, because of the cold hardening of the rail head tread metal, the hardness of the rail head is increasing, and the hardness can reach HB360 by the total mass 150. Thereafter, the hardening layer no longer changes, for carbon steel rails, Micro-cracks are formed on the surface of the rail head through the total mass 200. For the elastic unequal line when the wheel and the rails are obviously uneven, the tensile pressure on the top of the rail is almost equal, if there is micro-pattern, and the flexural stress and the residual stress are the same, the rail strength will be greatly reduced. The third stage is the formation of contact fatigue of rail head, due to the lack of metal contact fatigue strength and the multiple effects of heavy-duty wheels, when the maximum shear stress action point exceeds the shear yield limit, the point becomes the plastic region, the wheel will produce the metal microstructure slip every time, through the operation of a period of time, this slip generates accumulation and aggregation, resulting in the formation of fatigue crack. The initiation and development of contact fatigue crack will be accelerated with the improvement of axle load, transportation condition of large volume, rail material and rail type.