Theory And Method Research On Damage Tolerance Of The Hollow Axles Of High Speed Trains

The train works in a complex system and its running condition may become more sever with the speed increasing, and edge hard object impacts can occur on high speed tracks. Such events can leave sharp angled notches at the surface of axles. Under this condition cracks can initiate and grow to the critical size, which will bring great hide safe trouble.This paper is supported by the national basic research and develop project, the fatigue life and crack propagation life of the surface crack of hollow axles of the high speed train which is very important for the axles examine and repair management. The mainly work are as follows:1. Notched samples are made to simulate the impact damage from hard objects on the surface of axles. Using four-point rotary bending test, the S-N curves of different notched samples of axle steel were studied. The parameters change of S-N curves with different stress concentration factors were analysed.2. The stress spectrum under bending load was got on the basis of stress-time data of hollow axles using the rain-flow cyclic counter method. Using the statistic method we find that the stress spectrum accords with three-parameters Weibull distribution and the procedure stress spectrum was got. The effects of different railway line levels and the running conditions on the dynamic stress of axles by the equal stress are researched. The results indicate that the values of the rebuilt railway line are higher than that of the special railway line. On the basis of the researches above the service and design load spectrum are proposed for establishing the design standard of high speed train axles. At the same time the general dynamic load factors on the rebuilt railway line and the special railway line are evaluated comparing with that of the JIS standard and the EN standard. It is concluded that the JIS standard and the EN standard can not satisfied the damage tolerance limit design.3. The types and position from the foreign object damages and the physical model and the shape parameters of the notches are analyzed. The Finite Element model of the railway axle is built with which we can get the stress concentrator factors at the base of the notches. The Miner rule is used to calculate the fatigue life of the axle with a notch under the variable amplitude loading and the effect of the notch shape on the fatigue life is evaluated. 4. The geometry model of surface crack of a hollow axle is built, and the analytic formula of the stress intensity factor of the hollow axle surface crack is obtained by modifying that of the solid cylinder surface crack. The modified model considered the effect of inner surface of the hollow axle on the stress intensity factors. The stress intensity factor at the crack center point of different aspect ratios and depths are calculated using the analytic formula under the rotary bending load.5. The propagation characteristic and life of the short crack from different notches are estimated using the service loading and the EN13103 standard, it is indicated that the values under the service loading are higher than the design loading.6. The NASGRO equation is used to build the propagation model of fatigue crack and the propagation condition of the crack is analyzed. Because the shape of the surface crack changes with the crack depths and aspect ratios, the critical crack size are different under the given crack aspect ratios, so the relationship between the critical crack size and the crack aspect ratios is given. The propagation rules and residual lives of long cracks under service loading are executed...