Fatigue Strength And Damage Tolerance Assessment On Railway Axle With Inside Axle Boxes

Chinese high-speed railway operation mileage has reached 29,000 km at the end of2018,ranking first in the world.With the development of society and the progress of science and technology,the railway is developing in many aspects,such as high speed,light weight,excellent operation quality,low noise and environmental protection.Compared with the traditional axle with outside axle box,the axle with inside axle box has shown its advantages of light weight,small radius curve passing performance and so on.It has great application potential in urban rail and high-speed railway.And axle is an extremely important component of railway vehicle,its fatigue failure directly endangers the safety of vehicle operation.Therefore,it is of great theoretical significance and engineering guiding value to evaluate the fatigue service performance of the axle with inside axle box.The axle with inside axle box is taken as the object in this paper,the main research contents are as follows:The experiments of EA4T axle material was comprehensively carried out to obtain the basic mechanical properties,low cycle fatigue properties,high cycle fatigue properties,crack growth rate and fracture threshold.Considering the difference of geometric dimension,surface quality and loading mode between specimen and full-scale axle,the performance of full-scale axle is modified to provide basic parameters and reference for axle life calculation.The finite element model of the wheelset system with inside axle box is established.By setting reasonable contact parameters,the press-fit effect between the wheel,gear and brake disc and axle is simulated.The vertical load spectrum and boundary constraints are applied to the axle.And the critical safety position of the axle with inside axle box is located in the middle of the axle body which is not affected by the press-fit.It is obviously different from the traditional axle with outside axle box.Based on the modified linear Miner cumulative damage theory,the fatigue strength and service life of axle with inside axle box is evaluated by combining the high cycle probability fatigue S-N curve(fatigue P-S-N)of axle material and load spectrum.The fatigue life of full-scale hollow axle is predicted to meet the design requirements of 30 years or 10~9 loading cycles in the existing railway axle standard.However,damage tolerance design method based on fracture mechanics is introduced,and referring to the actual crack morphology of axle,the semi-elliptical cracks with different depths were implanted in the axle stress concentration area.Next,the stress intensity factors at the crack tip under the load spectrum were calculated.And then combining the crack growth rate model LAPS proposed independently by the research group,the residual life of axle is predicted.The results show that the fatigue life of the axle decreases obviously when there are defects on the surface of the axle.The nondestructive testing interval should be reasonably formulated to ensure the safety of the axle.In order to improve the fatigue fracture resistance of damaged axles,a surface strengthening method is proposed.Specifically,the residual compressive stress of axle surface strengthening layer is reconstructed by finite element method.From the point of view of simulation and calculation,it is shown that the residual compressive stress can inhibit the fatigue crack growth of axle.