Study On The Effect Of Residual Stress On Fatigue Crack Initiation And Propagation Of Rail

With the development of railway transportation,heavy haul railway has become the trend of the development of freight railway in our country,and the residual stress is one of the factors that affect the fatigue crack initiation and propagation of rail of heavy haul railway.It is of great practical significance to explore the influence mechanism of residual stress on fatigue crack initiation and propagation.In this paper,based on the theory of heat transfer,straightening deformation theory and fracture mechanics theory,the evolution of residual stress in the process of rail production and operation and the influence mechanism of the residual stress on the fatigue crack initiation and propagation are studied.First of all,an explicit dynamic finite element model and a thermal-mechanical coupled finite element model are established using ABAQUS simulation software to simulate respectively heat treatment and straightening of rail.And the stress state of the new rail is obtained after the straightening of the 75 kg/m heat treatment rail.Secondly,a finite element model of wheel/rail contact is established into which the residual stress in the process of rail production is imported.The evolution law of the residual stress of the rail of heavy haul railway in use is studied,the residual stress distribution of rail under different working conditions is analyzed.The results show that the wheel load impact on the stress distribution of the residual mainly concentrated in the contact area and the nearby.On the surface and near surface of contact area,with the increase of the number of wheel load,the residual stress tends to be stable.After 10 wheel loads,the distribution of longitudinal residual stress under the condition of pure rolling and 0.4% longitudinal creep rate are similar: the longitudinal compressive stress state is above 6mm,and the tensile stress is below 6mm.The influence of friction coefficient on the distribution of longitudinal residual stress and residual shear stress is mainly concentrated in the depth range of 2mm.Compared with the friction coefficient,the influence of wheel rail force on residual stress is greater.Then,based on the critical plane method and the low cycle fatigue theory,the effect of residual stress on the rolling contact fatigue crack initiation calculation of rail is studied.Considering the effect of residual stress,the influence of different working conditions on the fatigue crack initiation life of rail is analyzed.The results show that the residual stress has a great influence on the fatigue crack initiation life of rail.For a general condition,the fatigue crack initiation life under the condition of no residual stress is only about 75% of the residual stress.Considering the effect of residual stress,the bigger the friction coefficient is,the shorter the fatigue crack initiation life is;The bigger the wheel rail force is,the shorter the fatigue crack initiation life is;The higher the longitudinal creep rate is,the shorter the fatigue crack initiation life is.Finally,a three dimensional elastoplastic finite element model of wheel rail contact with oblique cracks is established,and the residual stress field produced during rail production and service is introduced.The fatigue crack tip displacement is taken as the fracture parameter,and the rolling contact fatigue crack growth characteristics under the condition of residual stress are analyzed.The result shows: When the crack is in the residual compressive stress state,the crack tip opening displacement CTOD amplitude under consideration of the residual stress is only about 28.9% of that without considering the residual stress;When the crack part is in the residual tensile stress state,the CTOD amplitude under consideration of the residual stress is about 180.8% of that without considering the residual stress.Therefore,the effect of residual stress should be considered in the analysis of rail fatigue crack growth.Considering the residual stress,the crack depth and the crack angle have a great influence on the crack tip opening displacement CTOD,the crack tip sliding displacement CTSD and the crack tip tearing displacement CTD;The friction coefficient of crack surface has a great influence on CTSD,and has little influence on CTOD and CTD;The fatigue oblique cracks of rail mainly extend in the compound mode of ?-? type or ?-?-? type.