Abstract: Aluminum alloy carbody is the key component of high speed train,the design of carbody needs to meet the requirements of ultra long fatigue life.In order to avoid fatigue failure and reduce test cost,the accelerated life test method is often used.The vehicle random load spectrum is calculated by the vehicle system dynamics method,load frequency diagram is obtained after processing load spectrum.Based on the FKM standard,acceleration load spectrums with 1×10⁷ cycles under three load ratio is made.Using the finite element method,the spectrum under three load ratio are applied to calculate the acceleration coefficient respectively.Based on linear and nonlinear cumulative damage theory,the effect of load spectrum loading sequence on accumulation of carbody damage is analyzed.The results show that the carbody structure fatigue damage is less than 1 when applied the original load spectrum and acceleration load,meeting the design requirements.Raising the load ratio to P=1/3 and P=2/3 respectively,the acceleration coefficient is corresponding to 12.75 and 218.65.The sequence of load spectrum loading has an effect on body fatigue cumulative damage,taking P=2/3 for example,the damage value accumulated up to 1 when high-low load spectrum cycles 632 times,while low-high load spectrum cycles only 614 times to reach the same damage value.It can be concluded that the vehicle load has the characteristics of low stress amplitude dominant,low-high loading sequence has better acceleration effect.Research on the Compiling and analysis method of the acceleration load spectrum of the carbody provides the theoretical basis and scientific guidance for the fatigue test of the carbody.

Key words: acceleration factor, acceleration life test, fatigue damage, high speed train, load spectrum