Analysis Of Vibration Modal Influence On Fatigue Life For High-Speed Train Carbody

With the extensive operation of high-speed trains in our country, the advanced technology and superior performance have been affirmed. The main characteristic of high-speed train different from ordinary trains is that the operation speed is larger than 200km/h. To achieve the purpose of high effective transportation, the speed of high-speed train is continued to improve. At the same time, high frequency and small amplitude loads on high-speed train structure become the dominated loads. In order to meet the requirement of vehicle lightweight, the application of aluminum alloy carbody will lead to significant changes of carbody mode characteristics. By analyzing the carbody modes and its effect on fatigue, the modes of high-speed train carbody can be controlled to avoid the harmful modes. The method has very important practical meaning to provide reference of vehicle dynamic design.Firstly, the finite element model of high-speed carbody was established. Based on the comparison and analysis of three design codes which are EN12663-2010:Railway applications-structural requirements of railway vehicle bodies, JIS E7106-2006:General requirements of railway vehicles passenger carbody and China code:Strength design and test methods of railway vehicles which speed is above 200km/h, the code EN12663 was chosen as the basis to analyze the static strength, stiffness and fatigue strength of carbody. Then the load cases were determined to evaluate the static strength, stiffness and fatigue strength. The computation results show that the static strength, stiffness and the fatigue strength meets the code requirement. The fatigue strength was evaluated by using the maximum principal stress method to convert the multiaxial stress to uniaxial stress.Secondly, the fatigue life of carbody was calculated by using quasi-static superposition method. To establish the vehicle system dynamics model and apply the railroad excitation, the random load time history of carbody at different speed levels were calculated. Combined the static strength analysis results under unit loads with the S-N curve of aluminum alloy, the fatigue damage under different speed levels of carbody were calculated using Miner linear cumulative damage theory. The fatigue damage results of quasi-static superposition method provided comparative data for subsequent consideration of fatigue damage under the effects of carbody modes.Finally, the fatigue damage of high-speed train carbody was calculated by modal superposition method. Firstly, the carbody modes at empty and preparation conditions were calculated to compare and analyze. Then the modal transient response time history of each modes were calculated through calculation of transient response. The modal stress of single mode and multiple modes superposition were calculated to combine with S-N curve of aluminum alloy and Miner damage theory. Then the modal effect on fatigue damage of carbody was analyzed and several modes which had large effect on fatigue damage of carbody were found.Based on the computation results, the quasi-static superposition method and modal superposition method to predict the carbody fatigue life are compared and analyzed. The results show that the carbody fatigue life on dynamic focus points calculated by modal superposition method is lower than the carbody fatigue life calculated by quasi-static superposition method. The reason is that the mode frequencies of carbody are excited by random load frequency domain spectrum after considering the effect of carbody mode frequency. The vibration influences due to modal superposition have large impact on the floor and window corner, which lead to the increase of fatigue damage on these parts; While the fatigue damage of quasi-static superposition method is calculated using Miner linear cumulative damage theory after the stress history was obtained by combining with the unit load static strength and random load time history, the results have no direct relationship with itself mode. Considering different operation speed, the fatigue damages were calculated according to the modal superposition method. The computation results show that fatigue damages of carbody were affected differently by the modes as the operation speed variation. The reason is that the improvement of speed lead to increase vibration of high frequency so carbody modes were excited to influence the fatigue damage differently.