Finite Element Simulation Of Fretting Fatigue Crack Propagation In Wheel Seat Of Railway Axle

The fretting fatigue damage in the interference fit part of the wheel seat is the main factor of axle failure.Fretting fatigue cracks are occasionally found on railway axle operating for a certain mileage during the flaw detection process.To ensure that the axle with fretting fatigue crack that missed the inspection can normally operate to the five-level repair mileage(1.2million kilometers),a prediction of the fretting fatigue crack growth life is needed to evaluate the residual operation mileage before axle failure.Based on the above requirements,a finite element simulation study on the fretting fatigue crack propagation in the wheel seat of axle was performed in this thesis.Firstly,the failure axle was sampled and observed,and the profile variation of wheel seat and the basic morphology characteristics of fretting fatigue crack were obtained.Subsequently,the fracture property test of axle steel material was carried out,which provides significant basic data for the further simulation of fretting fatigue crack propagation.Based on the measured fretting fatigue crack morphology and the surface profile of wheel seat,a finite element model of press-fitted railway wheel-axle with fretting fatigue crack was built in the finite element software Abaqus,the variation of stress intensity factor of fretting fatigue crack under rotary bending load was calculated through interaction integral method.Then,the maximum circumferential tensile stress criterion was adapted to determine the fatigue crack path,and the variation of fatigue crack growth driving force with crack length was obtained in the fretting fatigue crack propagation analysis.To predict the propagation life of fretting fatigue crack at wheel seat,Paris formula,modified Paris formula and NASGRO equation were used to fit the experimental data of fracture property of axle steel,and the corresponding crack growth rate parameters were obtained in this thesis.Then,by combining with the curve of crack growth driving force,the fretting fatigue crack growth life under constant amplitude load and stress spectrum load were calculated based on the numerical algorithm of fatigue crack propagation prediction.It is shown that the effective stress ratio can gradually change with stress level and crack length due to the interference fit between wheel and axle,even the stress ratio of the axle under rotary bending load is constant.Due to the neglection of stress ratio effect in Paris formula,an exceedingly conservative crack growth life will be obtained in the simulation.The modified Paris formula and NASGRO equation are capable to consider the influence of stress ratio on the crack growth rate,and a relatively close crack growth life can be obtained in both models.Without considering the rapid decrease of the crack growth rate near the threshold region,a relatively conservative life will be obtained in the modified Paris formula.However,due to the succinct style of modified Paris formula,it is more convenient to use in practical application.Based on the Miner’s linear damage accumulation theory and stress spectrum data in existing literature,the fretting fatigue crack growth life under stress spectrum load was calculated through modified Paris formula.It is shown that the residual operation mileage of axle is about 4.5 million kilometers when the crack propagates from the initial length to the rapid crack growth stage,the axle with fretting crack can normally operate to the inspection period.The research results in this thesis can provide a reference for deep understanding of fretting fatigue crack propagation behavior in the press-fitted part of railway wheel-axle,and provide a theoretical basis for the residual life prediction and operation safety analysis of the axle.