Growth Regularity Analysis Of Rail Rolling Contact Fatigue Crack Based On Random Load

With the development of heavy haul railways,the axle load and volume of trains are continuously increasing.As one of the types of rail damage,the rail surface fatigue crack is affected by multiple influencing factors,all of which have some randomness.It is of great significance to study the law of crack propagation under the single and common changes of all influencing factors.Based on the theory of fracture mechanics and the contact theory of rolling contact between wheels and rails,the mechanism of surface fatigue crack propagation during service of heavy haul railway is studied.First of all,a finite element model are established using ABAQUS simulation software to simulate wheel-rail contact.By comparing the fatigue crack growth rate and the crack tip displacement under the single influence factors,the results show that the characteristics of cracks including crack size,initial crack angle,and crack surface friction coefficient have a great influence on the fatigue crack propagation rate on the rail surface.For a specific shape of the crack,the friction coefficient of the crack surface and wheel-rail load compared to other factors have a greater impact on the crack propagation.With the increase of crack size and crack angle,the crack mainly expands in ?-? complex type which is dominated by type ?.Secondly,through orthogonal experimental design,consider the influence of wheel-rail friction coefficient,temperature stress,crack surface friction coefficient and load.It is found that the change of the friction coefficient of the cracked surface has a significant effect on the change of the amplitude of the equivalent stress intensity factor.The larger the friction coefficient of the crack surface,the larger ?keq.The fatigue crack growth rate of the rail surface under different crack sizes is greatly affected by the friction coefficient of the crack surface and the wheel-rail force load,and is less affected by the temperature stress and the wheel-rail friction coefficient.The fatigue crack growth rate of the rail surface under the different initial crack initiation angles is greatly affected by the friction coefficient of the crack surface and the wheel-rail force load,and is less affected by the temperature stress and the wheel-rail friction coefficient.Thirdly,the analysis predicts the direction of expansion of the rolling contact fatigue cracks on rails.It is found that in the entire crack leading edge,the expansion directions of the two ends near the rail surface differ greatly,and the difference in the middle part near the rail interior is small.The crack tip close to the rail surface extends in the same direction as the driving direction and extends forward at a different acute angle.Away from the rail surface crack tip expansion direction opposite to the driving direction,and torsion angle fluctuation is small.When the load is small,the extension directions of the two ends of A&B close to the rail surface are quite different.The smaller the load is,the larger the torsion angle is.As the load increases,the smaller the torsion angle of the crack tip.Judging from the crack front of a single crack,the increase of load makes the change of each crack front in the expanding direction relatively small.Finally,taking into account the randomness of the wheel-rail load,combined with the load spectrum of the small-radius curve track on heavy-duty railways,useing the maximum energy release rate criterion is,and the load classification and superposition method is adopted.It is found that the crack front depth increases with the change of the crack size of the rail surface from 2 mm to 6 mm.In this case,the crack kink angle increases from-50° to-65°.This shows that the increase of the crack size of the rail surface makes it easier to extend it in the direction opposite to the driving direction.When the initial angle of the rail surface crack changes from 30° to 55°,considering the superposition effect of the crack initiation angle and the crack propagation torsion angle,the crack propagation direction and the rail surface deflection gradually increase,resulting in the formation of hook-like cracks,which cause the surface cracks of the rails to become stripped off the rail surface.