Experimental investigation of high-speed wheel-rail adhesion characteristics under large creepage and water conditions

With the increase of train operational speed, the wheel-rail adhesion will behave differently. This behavior will directly affect the utilization of wheel-rail adhesion during traction and braking. Typical rainy and snowy weather will cause the wheel-rail low adhesion problem. Correspondingly, the wheel sliding can happen and causes wheel burns on both the wheel and rail contact surfaces. Besides, the braking distance will exceed the limit, which endangers driving safety. The engineering application of brake adhesion of high-speed EMUs mainly utilizes the second peak of braking force coefficient (it refers to the instantaneous adhesion force coefficient during the braking process.) under large creepage through anti-skid braking system, where the braking force coefficient reaches its maximum value at this second peak [11]. However, this wheel-rail adhesion behavior and the underlying mechanism are complexed especially under the high speed, which restricts its effective use for high-speed trains. In this paper, an innovative full-scale high-speed wheel-rail test rig is used to investigate the high-speed wheel-rail adhesion characteristics under large creepage and water conditions. The influence of different test speeds of 100-400 km/h is considered. Based on the test, it is found that the braking force coefficient is influenced by the test speed. Therefore, the optimal "beneficial zone" where the braking force coefficient has the maximum value and, in the meantime, guarantees the wheel-rail contact in stability varies with speed. The test results provide a fundamental basis for improving the utilization of EMU braking adhesion.