Influencing factors of rail burn formation for high-speed railway

The ANSYS explicit dynamic analysis was employed to build a three-dimensional transient wheel-rail contact mechanical-thermal coupling finite element model with the influence of temperature on the thermo-elastoplastic material parameters taken into consideration. Under the working conditions of an initial temperature of 30 ℃, an axle load of 16 t, an initial speed of 300 km·h^-1, and a slip-to-roll ratio of 30%, the contact pressure, effective plastic strain, temperature distribution and its variation characteristics of the rail tread were studied at the earlier, middle, and later moments when the wheel passed by the typical rail sections. On this basis, the influences of the train axle load, rail tread state, as well as the train traction and braking states on the maximum temperature rise and maximum contact pressure of the rail tread were further analyzed, and the formation mechanism of rail burn was discussed on the basis of the formation mechanism of the martensite white etching layer of rail. Research results show that under the calculation conditions of this paper, the maximum contact pressure of the rail tread is 1 186.43 MPa, which appears at the center of the contact zone. The residual thermal and mechanical stresses inside the rail can be found after the wheel passes. The maximum effective plastic strain of the rail is 0.028 2. The maximum temperature rise is 554.55 ℃. When the train axle load increases from 12 t to 16 t, the maximum temperature rise of the rail increases from 339.89 ℃ to 402.79 ℃. When the friction coefficient of the rail tread increases from 0.2 to 0.6, the maximum temperature rise of the rail increases from 230.93 ℃ to 519.25 ℃. When the slip-to-roll ratio increases from 10% to 40%, the maximum temperature rises of the rail caused by the wheel braking and traction increase from 264.52 ℃ to 700.46 ℃ and from 362.10 ℃ to 819.61 ℃, respectively. Under the same slip-to-roll ratio, the maximum temperature rise of the rail caused by the traction condition is more significant than that caused by the braking condition. In particular, when the slip-to-roll ratio increases to 40%, the maximum temperatures of the rail tread are 700.46 ℃ and 819.61 ℃ under the braking and traction conditions, respectively. The maximum temperature rise of the rail is higher than the phase transition temperature. As a result, a martensite white etching layer on the rail tread is formed to develop rail burn on the rail tread.