Fatigue Life And Damage Tolerance Assessment On Bogie Frame Of Railway Vehicles

The total mileage of Chinese high-speed railway network almost approached 30000 km at the end of 2017,and it is expected to reach 38000 km in 2025.Safety and durability have become the most important attention.Among all safety-critical structures,the high-speed welded bogie frame is well-known to play a crucial role in transferring the static load from vehicle weight to hollow axles,besides controlling wheelsets on straight and curved tracks and supporting the wheels,axles,brakes and suspensions.For the bogie frame of high-speed train,the load of the bogie is much more severe.The fatigue strength of welded frame will directly affect the safety,stability,comfort and economy of high-speed train.Theoretical aspect: five methods for evaluating fatigue strength of welded structures are introduced: nominal stress method,hot spot stress method,notch stress method,master S-N curve method and fracture mechanics method.This paper compares three typical theories of fatigue cumulative damage and presents the fatigue design methods commonly used in engineering practice.Experimental aspect: the basic mechanical property,fatigue property and fatigue cracking resistance of the base metal and welded joint are comprehensively investigated by various methods,such as metallographic experiment,hardness test,monotonic tensile,low cycle fatigue,high cycle fatigue,fatigue crack propagation threshold and crack growth rate.Simulation aspect: high quality hexahedral elements including welding seam of welded bogie frame are carried out with HyperMesh software.According to the standard UIC615-4 and EN13749,the operating loads and corresponding boundary conditions apply on the bogie frame.Based on the fourth strength theory and modified Goodman curve,the static strength and the fatigue strength are evaluated,respectively.Finally,the life evaluation of the key parts of the bogie frame are conducted.A possible incomplete fusion defect is assumed at the welding seam of primary spring.To compare with stress intensity factor threshold,the stress intensity factor amplitude of the defect tip is calculated by stress intensity extrapolation method.Combined with the 8 stage measured brake load spectrum,the damage calculation of the brake unit bracket are obtained by the Miner cumulative damage theory.Based on the damage tolerance analysis,the semi-elliptical cracks with different depths are inserted into the maximum stress region of brake unit bracket.It is convenient and accurate to acquire the crack propagation rate with NASGRO model,and predict the residual mileage of brake unit bracket.The life assessment results show that the safe operating life of the above parts can satisfy the service life of the frame for 30 years.