Investigation On Dynamic Response Of Wheel-rail Rolling Contact In Welded Joint Of Highspeed Rail

With the rapid development of China’s high-speed railway,the safety and running quality of high-speed railway system have attracted more and more attention.The use of flash welded seamless rails has greatly improved the stability and comfort of train operation.However,due to the non-uniformity of the material at the rail welded joint,it is more likely to be damaged and destroyed than the rail in the non-welded region.The rail welded joint has become the main damaged position of current seamless rail line.In order to evaluate the service performance of welded joints in the wheel-rail rolling contact of high-speed railway,the quasi-static and dynamic impact experiments on the flash welded joint of U75 VG rail in high-speed railway were carried out,the basic material mechanical properties and dynamic mechanical properties in each region of welded joints were obtained.Then,based on the experimental results,a dynamic constitutive model for welded joints of U75 VG rail steel was established.Finally,the finite element software ABAQUS was used to analyze the mechanical responses during the wheel-rail transient rolling contact.The research results will provide a basis for evaluating the service performance of rail welded joints in high-speed railway.The main content of this work is as follows:(1)The non-contact digital image correlation technology was used to perform quasi-static uniaxial tensile tests on flash welded joint samples of U75 VG rail at room temperature,and the distribution of each region of the welded joints was determined.Then,the quasi-static tensile tests and SHPB tests of base metal(BM),welding zone(WZ)and heat affected zone(HAZ)were carried out,respectively.The basic material mechanical properties and stress-strain curves at different loading strain rates were obtained.The results show that the widths of WZ and HAZ in flash welded joints of U75 VG rail are about 30 mm and 20 mm,respectively;the strength in the WZ is similar to that of BM,and the strength of HAZ is significantly lower than that of BM and WZ;the strength of WZ is similar to that of BM,and the strength of HAZ is significantly lower than that of BM and WZ;all materials of BM,WZ and HAZ show strong strain hardening and strain rate hardening effects.(2)Based on the dynamic mechanical properties in each region of rail welded joints obtained from experiments,the applicability of the dynamic mechanical response in each region of rail welded joints was evaluated against the classic J-C model and existing modified J-C models,respectively.By introducing the correlation coefficient of material strength in each region of rail welded joints into the strain hardening and strain rate hardening terms of J-C model,a modified dynamic constitutive model suitable for the flash welded joint of U75 VG rail was established.The implicit stress integration algorithm was used to implement the modified model into the finite element analysis software ABAQUS,the simulated results showed that the proposed model reasonably predicted the dynamic mechanical responses in various regions of welded joint at different loading strain rates.(3)In order to analyze the dynamic mechanical responses of rail welded joints in wheel-rail transient rolling contact of high-speed railway,a finite element analysis plug-in for wheel-rail rolling contact at the welded joint was developed based on the finite element analysis software ABAQUS.According to different welded parameters,the rail welded joint modeling and finite element analysis of wheel-rail transient rolling contact can be quickly completed.The dependences of dynamic mechanical response of rail welded joints on the non-uniformity of materials and service conditions were revealed.The researched results show that the maximum contact stress in the HAZ is smaller than that in other regions,and the stress concentration will occur at the junctions of BM and HAZ,HAZ and WZ,respectively;and the peak value of equivalent plastic strain appears at the junction of HAZ on the secondary surface of rail and WZ;compared with the results in the quasi-static analysis,and the equivalent plastic strain of welded joints is greater than that in the dynamic analysis;the maximum contact stress increases with the increase of axle load,and small fluctuations in the axle load have little effect on the peak value of equivalent stress,the distribution of strain fields and the peak value of equivalent plastic strain rate;the maximum contact stress first increases and then decreases as the driving speed increases,and the peak equivalent stress increases as the driving speed increases;due to the competition between strain hardening and strain rate hardening,the driving speed has significant effects on the equivalent plastic strain rate and strain distribution.