Multiaxial Fatigue Life Prediction Of High-speed Maglev Train Levitation Chassis

As one of the development directions of rail transit technology,high-speed maglev transportation can make up the speed gap between high-speed rail and air passenger transport,which is of great significance to improve China’s high-speed passenger transport system.The existing operation experience of rail transit equipment shows that the fatigue failure is one of the main failure modes of vehicle bearing structures.Levitation chassis as the important bearing structure of high-speed maglev must have enough fatigue life to ensure the operation of the train safely and reliably.Considering the non-proportional multiaxial loads borne by vehicles in service and the complex geometry of the structural components,the key parts of the bearing structure are likely to be in the state of multiaxial stress.The analysis results of multiaxial fatigue theory,which can consider more factors causing fatigue damage,are more practical.Taking the TR series of high-speed maglev train of Germany as the research object,this thesis presents a study of levitation chassis fatigue life on higher speed level based on the multiaxial fatigue theory,multibody dynamics simulation analysis and finite element analysis.Firstly,the applicability of four multiaxial fatigue life prediction models based on the critical plane method were analyzed according to the multiaxial fatigue experimental data of 6 series high strength light aluminum alloy,which is the main material of levitation chassis.Choose Wang model and Kluger mode with high prediction accuracy as the multiaxial fatigue life prediction model of the Levitation chassis.Secondly,a detailed finite element mode of levitation chassis was established,and the dynamic fatigue load of levitation chassis was obtained by the simulation of multi-body dynamic simulation under operation conditions of maglev train based on the existing maglev line conditions in China and the design goal of high-speed maglev train on higher speed level.The quasi-static superposition method was used to analyze the dynamic stress combined with the finite element and fatigue load of levitation chassis.Then,according to the structure and process characteristics of the Levitation chassis,the corrected S-N curves were determined on the basis of Eurocode 9 standard.The uniaxial fatigue life prediction mode of levitation chassis was established combined with the dynamic stress,Miner’s linear fatigue damage accumulation rule and S-N curves.The uniaxial fatigue life of levitation chassis was evaluated and the hot spots of fatigue damage was identified.Finally,took the hot spots of fatigue damage as the test points and analyzed their stress state.According to the Wang model and Kluger model,the history of fatigue damage parameters on the critical plane of each test point were calculated,and the multiaxial fatigue life prediction models of the levitation chassis were established combined with the multiaxial fatigue cycle counting method,corrected S-N curves and Miner’s linear fatigue damage accumulation rule to evaluate the multiaxial fatigue life and compared with the uniaxial fatigue results.The results show that the fatigue damage distribution trends calculated by uniaxial fatigue model,Wang model and Kluger model are consistent and they all find out the main weak positions of levitation chassis includes the connection position between pendulum and inside bolster,bolt connection positions of bracket fittings and bolt connection positions between bracket and suspension electromagnet.Among them,the fatigue life of the levitation chassis calculated by uniaxial fatigue life model is 12.8 million km,while the multiaxial fatigue life of the levitation chassis calculated by Wang model and Kluger model is 3.981 million km and2.955 million km respectively.It is found that the most of the damage hot spots on the levitation chassis are in the state of multiaxial stress through the analysis of ‘biaxial rate’,which leads to the evaluation results of uniaxial fatigue model are more dangerous.Especially when the biaxial ratio is more than 0.15,the difference between uniaxial fatigue life and multiaxial fatigue life are more than three times.While the fatigue life calculated by the multiaxial fatigue model based on the critical plane criterion are more conservative because more factors causing fatigue damage are considered.In order to improve the operation safety and structural reliability of maglev train on higher speed level,it is suggested to focus on the fatigue weak positions of the levitation chassis in the structural design or optimization stage,and consider the influence of multiaxial stress state in the fatigue life prediction.The analysis results of this thesis can be used to improve the structure design of levitation chassis of the existing maglev train,and provide a new way for the fatigue life prediction of levitation chassis structure,which has certain engineering value and theoretical significance.