Analysis Of Fatigue Strength Reliability For High Speed Train Carbody

Compared to traditional railway vehicle, high speed train has many differences. High speed train is driven by fixed group and power distributed driving mode, and the operating speed is generally higher than 200km/h. The hollow aluminum alloy extrusion profile is largely used in design of high speed train while the floor longitudinal beam and cross beam structure are canceled. For high speed train, the vehicle equipments are suspended under carbody, resulting that the center of gravity of carbody becomes lower and the installation space is saved. The structure and the material of high speed train carbody are changed, at the same time, the requirement for structure reliability is improved. Once the structural fatigue reliability problem occurs, the consequence will be very serious. This paper takes a high speed train carbody as the research object, the reliability of fatigue strength will be studied, which can provide reference for the analysis method of high speed train carbody.Firstly, the finite element model of high speed train carbody was established. Based on the contrast and analysis of three design standards, which are EN 12663-1, JIS E 7106 and <Interim provisions of strength design of railway vehicles above 200km/h speed level and identification test>, the static and fatigue load conditions considering the aerodynamic load were determined. Combined with the strength performance data of the carbody aluminum alloy material, the Goodman curve of the car body material was drawn. After the finite element analysis of the carbody, the fatigue strength of the car body was analyzed based on the maximum principal stress method, and the safety factor of static strength and fatigue strength of the carbody with different reliability was gotten. This method of evaluating the static strength and fatigue strength of the carbody has a reference value to the traditional standard design method.Then, vehicle system dynamic model of high speed train was established, and the load spectrum of air spring position was obtained. Polynomial fitting method was used to transform the dynamic load to the dynamic stress. The stress block spectra were obtained by rain flow counting method and the probability density function was determined. Based on the dynamic stress strength interference model, the reliability and failure rate of concerned position on carbody was analyzed under the condition of considering strength degradation or not considering strength degradation. With the increase of the service mileage, the reliability of carbody decreases. The fatigue strength reliability of door area declines significantly. When the strength degradation is considered, the fatigue damage is accumulated, which results in the fatigue strength reliability decreases more obviously. The failure rate curve shows that with the increase of the train service mileage, the car body fatigue strength failure rate has a rapid decline, and then gradually increased. The failure rate curve can provide reference and advice for the reliable service life and maintenance.Finally, probabilistic finite element model of carbody was established. The material properties, carbody geometry parameters and the loads were all considered as random variable. Based on the Monte Carlo simulation method and the response surface method, the parametric sensitivity of carbody was analyzed. The results of these two methods are consistent, and the response surface method greatly reduces the solution time, which is more suitable for the parameter sensitivity analysis of the large complex structure like the carbody. The parameters which have big influence on carbody reliability are obtained by analysis, those parameters should be controlled strictly in the design and manufacturing process. The parameters which have little influence on carbody reliability can reduce redundancy by structural optimization.