Surface Crack Growth Simulation And Remaining Life Assessment Of High-speed Train Axles Based On Extended Finite Element Method

High-speed train axles are subjected to complex loads and various challenges during service.When surface defects are introduced due to scratches,foreign objective damages(FOD),etc.,cracks may initiate from the defects and further propagate,thus resulting the failure of axles.In order to analyze whether the axle with the crack meets the service requirements,its fatigue crack growth life need to be evaluated.In this thesis,based on the extended finite element method(XFEM),the surface crack stress intensity factor(SIF)and fatigue crack propagation behavior of EA4 T axle steel was investigated,and the residual fatigue life of the axle with the crack was evaluated,the thesis could provide provided a certain theoretical basis and reference for the determination of axle damage detection and maintenance cycle.The main content of the thesis is as follows:Compressive residual stress(CRS) was introduced on the rotating bending fatigue specimens of EA4 T axle steel by micro-shot peening(MSP),crack replica experiments were conducted for the un-peened(UP)and MSP specimens,respectively to obtain the curve of the crack length versus the loading cycles.The finite element models(FEM)of the rotating bending fatigue specimens was established to compare the result of XFEM,conventional FEM,and reference calculation.The results indicated that the CRS showed inhibition in the initial crack propagation,XFEM could effectively simulate the propagating SIF of surface crack under bending loads.The effects of the deflection mode and aspect ratio under tension-compression load,and rotation angle and depth ratio under rotating bending load,etc.,on the variation in the SIF of surface crack was investigated.The SIGINI subroutine associated with Abaqus was used to import CRS on the model surface,so as to study the effect of CRS on the crack propagation behavior.The results showed that the maximum SIF of the crack front was achieved when there is no deflection,and as the crack propagated,the aspect ratio attained approximately0.65 eventually.The CRS exhibited an obvious inhibitory effect on the initial crack growth,and as the crack further expanded,its effect gradually decreased.The full-scale FEM model of the hollow motor and trailer axles for the high-speed train were established,the critical crack size under the maximum loading stress of the motor and trailer axles at different positions was determined on the basis of the measured load spectrum.The simulation also analyzed the critical crack size for the motor and trailer axles,respectively,and the residual life of the motor and trailer axles at the axle body and transition of the wheel seat was evaluated considering the safety factor of damage tolerance.The simulation results demonstrated that when the crack size is the same,the crack located at the transition of the wheel seat showed higher propagation rate and less residual life than than that located at the axle body.The motor axle with crack was easier to reach fatigue failure than the trailer axle with crack at the same loading condition,crack size,and distribution location.In order to guarantee the safety and reliability of axle during service,different non-destructive testing(NDT)cycles should be reasonably developed for the different axles.