Dynamic constitutive model of U75VG rail flash-butt welded joint and its application in wheel-rail transient rolling contact simulation

Rail welded joint is one of weak links in high-speed railway, and its dynamic performance has important effects on the safety, stability, and comfort of the high-speed train. In this work, the dynamic mechanical responses at different regions of U75VG rail flash-butt welded joint were investigated. The results show that the base metal (BM), welding zone (WZ), and heat-affected zone (HAZ) of U75VG rail flash-butt welded joint has an obvious strain rate effect, i.e., the material strength increases with increasing the loading strain rate. The strength of WZ is similar to that of BM, but its toughness is much lower than that of BM. The toughness of HAZ is the same as that of WZ, but its strength is much lower than that of BM and WZ. Based on the experimental results, an improved dynamic constitutive model was established to reasonably simulate the stress-strain curves of different regions from quasi-static loading to dynamic loading. Finite element (FE) analysis of transient rolling contact between rail welded joint and wheel under different conditions was performed. Compared with the results from quasi-static wheel-rail contact simulation, the equivalent plastic strain at each region of rail welded joint increases significantly and presents non-uniform distribution after considering the dynamic effect. When the wheel contacts the junction between different regions, the impact will cause a significant stress concentration at the rail welded joints. The maximum wheel-rail load by the implicit dynamic analysis is about 4 similar to 12 times that obtained by the quasi-static analysis. Moreover, the maximum contact pressure, equivalent stress and equivalent plastic strain of each area of rail welded joints gradually increase with the increase in axle load and driving speed.