Study On Growth Behavior Of Fatigue Crack Of Rail

High speed and heavy load are the long-term development directions of the railway in our country. With the development of high speed railway and heavy haul railway, the damage of the rail has been increasing year by year. As an important form of rail damage, rail fatigue crack not only influences the comfortability of the rail, but causes some safety problems. So, it contributes to judge the degree of risk for the crack in the rail correctly by make the study of rail fatigue crack. Based on the research, the corresponding measures to prevent the safety accidents and to reduce the maintenance cost of the rail are taken. It can also make good sense to use the rail reasonably and extend the life of the rail.The three-dimensional model of the rail is built by using finit element method,the moving load mode based on the Hertz contact theory is adopted. The difference of growth behavior of crack under the action of group load and single load is analyzed.The propagation characteristics of rail crack located differen position under the group moving load and the influence of the parameters on the rail are studied. The influence of the parameters include: angle of the crack, depth of the crack, vertical force between wheel and rail, temperature stress, and bearing stiffness of the track. Through the fatigue crack growth rate test, the growth rates parameters of U78 CrV rail were fitted.The fatigue propagation life of the rail head nuclear injury is predicted, and the effect of crack angle on fatigue life is analyzed. The main conclusions of the paper are as follows.(1)Under the action of group load and single load, the crack propagation characteristics have obvious difference.The group load is more closed to the fact, the stress intensity factor varies periodically with moving load. Under the action of a single load, the stress intensity factor and stress intensity factor amplitude of crack are higher than under the action of group load. In the actual maintenance, the conservative measures will be adopted by using the results of the single wheel load.(2)The more closed to the surface of rail, the more complex of the nucleusflaw,the stress field and crack growth rates of crack tip are more larger.Then the nucleus flaw is more dangerous.(3)The angles between the crack surface and the cross section of the rail have remarkable influence on the crack propagation. With the change of the angle, the crack growth type will change.(4)The change of temperature stress has a great influence on the crack propagation properties, mainly affected the propagation properties of I mode. When drop in temperature, the crack is in a more complicated propagation type, the SIF and the growth rate of crack are greater, and the crack is in a dangerous state. And the temperature is lower, the more dangerous the crack. And when heating up, the SIF is very small, the growth rate is very slow, and the crack stops grow.(5)The C and m of U78 CrV rail crack growth rate formula of Paris is 4.813and1910727.7-?. Under the same conditions, when the stress intensity factor amplitude is larger, the crack growth rates of U78 CrV rail are larger than U75 V rail.The angle of nucleus flaw is 0°and 30°~45°, then its fatigue propagation life is lower, more dangerous.