Load Spectrum Compilation And Fatigue Life Prediction Simulation Of Accelerated Life Test For High-speed Train Carbody

During the service process,due to various factors such as track irregularity,the high-speed train carbody will be subjected to random loads,which are prone to fatigue failure and pose a threat to passenger safety.To ensure the safety and reliability of the high-speed train structure,the fatigue test should be carried out in the structural design stage to predict the fatigue life.As the running speed of high-speed trains is constantly increasing,the random load of the carbody is mainly high frequency and low amplitude,which makes it have long life and high reliability design requirements.If the traditional life test is used,a lot of time and resources will be consumed.Therefore,the accelerated life test(ALT)method is adopted in the design stage to quickly obtain the fatigue weak position of the carbody,and on this basis,the quantitative prediction of the fatigue life has important engineering significance and application value for the carbody design.Referring to the FKM standard and the UIC standard,combining the ALT,vehicle system dynamics simulation,finite element method,polynomial fitting method,structural stress method and linear damage theory are used to compiled the load spectrum of ALT and quantitative prediction of fatigue life for the carbody.Firstly,the accelerating load spectrum is compiled.The vertical random load spectrum of the carbody is calculated by dynamic simulation.After rain-flow and extrapolation,it is compiled into eight-stage load spectrum based on the FKM standard.Based on the UIC standard load spectrum compilation principle,combined with the fatigue load design of the vehicle in the EN12663 standard,the vertical load is compiled into a three stage load spectrum.Secondly,the numerical simulation is used to calculate the fatigue damage of the carbody under the accelerated load spectrums.The finite element model of a carbody is established,and the finite element analysis is carried out by the design conditions of the load spectrums.The simulation results are compared with the stress results of the rig test to verify the accuracy of the simulation results.The acceleration coefficient and fatigue damage of concerned points are calculated by combining the simulated stress results.The effects of the two load spectrums on the fatigue damage of the carbody are compared and analyzed.It shows that the eight-stage load spectrum is more suitable for the fatigue analysis of the carbody structure.Thirdly,the dynamic stress calculation of the carbody under random acceleration load spectrums.To simulate the phase relationship between loads during the ALT of the carbody,the eight-stage load spectrum is randomly sampled and combined,and compiled into a multi-axis random acceleration load spectrum containing phase information.The carbody surrogate model is established by the polynomial fitting method,and the random acceleration load spectrums of the carbody are converted into dynamic structural stress histories.After the correction,the equivalent structural stress range of the concerned points is calculated.Based on the principle of equal damage,the eight-stage effective structural stress spectrums are obtained.Finally,the fatigue life of the carbody is predicted.Combined with the master S-N curve,the fatigue damage value of the concerned points after 10~7 cycles of the random acceleration load spectrum is extrapolated.The dynamic structural stress and the equivalent structural stress range under the original load spectrum is calculate,the fatigue damage value and running mileage of the carbody are obtain,and combine the damage principle to estimate the fatigue life result of the carbody under the random acceleration load spectrum.The results show that the eight-stage load spectrum is more suitable for the ALT of the carbody structure than the third-stage load spectrum.Referring to the random acceleration load spectrum compiled by FKM standard,which contains the phase relationship between loads,and it can more realistically simulate the loading process of ALT for the carbody.Since the structural stress method can eliminate the dispersion of the S-N curve data in the nominal stress method and has mesh insensitivity to the stress calculation at welds,the fatigue results obtained by the structural stress method are more conservative than the nominal stress method.And it can improve the accuracy of life prediction.The research provides a reference method for the load spectrum compilation and prediction of the quantitative fatigue life in ALT of the carbody.