Study On Rolling Contact Fatigue Of U75V Rail During Curve Passing Of High-speed Train

Railway is the main artery of the national economy,a major livelihood project and key infrastructure.It is the backbone and main mode of transportation of the comprehensive transportation system,and plays an important role in China’s economic and social development.In service,the ratcheting effect induced by the cyclic rolling loading is one of main reasons for fatigue failure of rails.With the prolongation of the service life of rails in China,the problem of its damage is becoming more and more prominent,which has a significant impact on the safety,stability and comfort of the train.Hot-rolled and heat-treated U75 V steels have been widely used in straight and curved sections of high-speed railway,the curved rail passing by the train is the weak spot of the line,the wheel-rail force increases significantly when the high-speed train passes curvedly,and the damage forms,such as surface cracks,peeling,nuclear damage and honeycomb cracks appear more frequently in the curved rail,it is of great significance to analyze the fatigue damage rule of rails in curved section to improve the running stability of train and avoid the traffic accidents caused by fatigue.Therefore,based on the experimental results of U75 V steels ratcheting-fatigue interaction,the cyclic plastic constitutive model was selected and the fatigue failure model was established.Then,the wheel-rail force was obtained by multi-body dynamics simulations.Finally,based on the three-dimensional rolling contact finite element analysis,the fatigue damage mechanism of high-speed train curve passing through rail was revealed.The main work of this paper is summarized as follows:(1)Uniaxial tension,strain-controlled fatigue and stress-controlled ratcheting-fatigue interaction experiments were carried out for the hot-rolled and the heat-treated U75 V rail materials.It is found that both U75 V rail materials show good strength and ductility.The cyclic softening characteristic is observed under the strain-controlled cyclic loading,while the ratcheting behavior is observed obviously under the asymmetric stress-controlled cyclic loading.The fatigue lives of two kinds of rail materials increase with the increase of the stress amplitude;However,they decrease first and then increase with the increase of mean stress.By comparing the experimental results of U75 V rail materials,it is found that the heat-treated U75 V rail material has higher strength,ratcheting deformation resistance and fatigue resistance.(2)The improved Abdel-Karim-Ohno model was used to simulate the uniaxial tensile curves,cyclic stress-strain curves,cyclic softening characteristics and ratcheting strain evolutions of U75 V steel by two heat treatment processes.Considering the influence of stress amplitude and mean stress on the fatigue life,based on the existing equivalent stress,a modified equivalent stress was defined,and the failure life prediction model was established to accurately predict the fatigue life of the hot-rolled and the hot-treated U75 V rail materials.(3)The rigid flexible coupling dynamic model of CRH380 B EMU-Curvilinear Track is established by SIMPACK with reference to the current high-speed railway design code.The influence of design superelevation,circular curve radius and transition curve length on the wheel rail interaction is analyzed.The results show that the vertical force of wheel and rail increases with the increase of over/under superelevation,while the circular curve radius increases or decreases on both sides of the superelevation at fixed superelevation,and decreases with the increase of transition curve length.The maximum lateral force of wheel and rail decreases with the decrease of superelevation and exhibits a contrary trend when the design superelevation is relatively small,it decreases with the decrease of circular curve radius and exhibits a contrary trend when the radius of small circular curve is relatively small at fixed superelevation,and the transition curve length does not affect the lateral force of wheel and rail.The lateral movement of wheelset decreases with the increase of superelevation,and the circular curve radius at fixed superelevation and the transition curve length have little influence on the lateral movement of wheelset.(4)Combined with constitutive simulation of the hot rolling and the heat treatment U75 V steel and the results of multi-body dynamics simulation,a finite element model of wheel rail rolling contact was established.Firstly,the distribution and evolution of stress and strain in the target section of rails during the rolling process of the wheel was analyzed.Then,the influences of design superelevation,circular curve radius and transition curve length on the stress distribution and crack initiation life in target section was indicated.It is found that the crack initiation life is lower when the under/over superelevation is larger.At both sides of the superelevation,the crack initiation life decreases with the increase of circular curve radius or the decrease of crack initiation life,and then it increases first and then tends to be constant with the increase of transition curve length,the influence of transition curve length on the crack initiation life depends on the design superelevation.Finally,the fatigue performance of the hot-rolled and the heat-treated U75 V rails during curve passing of the train was compared.It is found that the residual stress and accumulated plastic strain of hot-rolled rail change greatly,while the peak stress and crack initiation life of heat-treated rail are higher than those of the hot-rolled rail.