Abstract: Based on the modal displacement response the time history of modal stress of car body is determined by the method of modal stress recovery theory.Then the fatigue life of carbody is evaluated by the Miner accumulated fatigue damage theory.According to the analysis of influence of mode of vehicle on the fatigue life,the first ten modes of carbody with low frequency has the great influence on the fatigue life of car body,but the modes with high frequency has little effect on the fatigue life.Meanwhile by the analysis of influence of single mode on the fatigue life of the various parts of carbody,the first order vertical bending mode of carbody has the bigger impact on the fatigue life of carbody.

Key words: rigid-flexible coupling dynamic, modal superposition method, modal stress recovery method, carbody fatigue