Predicting Fatigue Life Of Rail Vehicle Welded Structure Based On Virtual Fatigue Test

As China's railway develops towards the high-speed and the heavy load one, railway vehicles' accidents of fatigue are occurring, once fatigue fracture is apper in key positions, the consequences will be serious. Vehicle's fatigue governance is a pressing need to the safety of rail transport. Weld is main connection for rail vehicles structure, is also prone to fatigue failure of the danger zone. Currently, fatigue problem can not be described theoretically as a united physical and mathematical model because too many factors effect structure fatigue. So, fatigue research mainly focus on the test step both inland and abroad, and the more to the research on welding structure. Whole vehicle fatigue experimentation needs physical prototype, a high cost, a long cycle, and complex random load, so it is still impossible now. Therefore, scientific prediction of fatigue life of the rail vehicle's welded structure is important theoretical value and engineering significance to the structure reliability design and safety assessment of the rail vehicle.Based on the summary of the domestic and foreign studies on the welded structure fatigue and the rail vehicle's fatigue life prediction, take rail vehicle body and its key component -Bogie welding structure for studying, from theoretical method, numerical simulation, the program, conducted a series of in-depth research. To sum up, the research work and achievements are as follows:After detailed analysis of the basic theory and prediction methods of welded structure's fatigue life, and defeat the difficulty of fatigue life prediction without physical prototype, on basis of virtual fatigue test, rail vehicle's welding structure fatigue life prediction technology route is proposed; finite element modeling method and choice principle of fatigue life evaluational points are given; and the solutions to key technology, such as test loading mode, dynamic stress virtual conversion and multi-channel load fatigue life prediction methods and so on, are given.As welding structure standard of rail vehicles' fatigue evaluation is rarely found, and the United States' AAR standard is only developed to use in railway wagon, so that in the virtual fatigue test, the widely used international Welding Association standard IIW and the British Standard BS are introduced. So as to enrich the fatigue characteristic parameter of welding structure, and to expand the scope of the prediction of welding structure. Through the systematic research of the three standards, the characteristics of welding structure's fatigue life evaluation method under the these standards are generalized, and engineering application reliability of virtual fatigue test is verified by means of welding structure fatigue life prediction of bogies under standard IIW. The reverse problem of the structural fatigue life evaluation is to set down the design details of the structure under a given product fatigue life. There exists the uniqueness of the data flow in process of the fatigue life evaluation under the AAR tandard, so from mathematics view, reverse calculating structural stress is available. Theoretical expression of a converse problem considering multi-load spectrums is derived to predict fatigue life of wagon body based on American AAR standard. The result shows that the means can be used to not only efficiently calculate the body structure design stress under a specified fatigue life but also theoretically provide improved design scheme to achieve wagon equivalent life design.In order to rapidly predict fatigue life for production structure including design details on welding line to wagon body-designers, fatigue life prediction software system is developed. Base on secondary development technolgy, it embedded in the large-scale finite element analysis software- I-DEAS. The system was developed with Visual Studio.NET and in which the stress detail of FEA result can be picked up in I-DEAS Post Processing by man-machine interact way. By using the system, the equivalent stress, fatigue damage data, the sum data of designal life and report file can be automatically calculated and generated respectively. The system contains load spectrum database of the AAR standard and the database can be conviently expanded.In this paper, four innovations are given as follows:1. A practical analysis method is presented to achieve fatigue life prediction of vehicle welded structure ahead of physics specimen.2. Theoretical expression of a converse problem considering multi-load spectrums is derived to predict fatigue life of wagon body based on American AAR standard. The theoretical expression is applied to an exported wagon.3. From the point of fatigue resistance, an important local design or reinforcement principle -stiffness coordination is proposed. Thereby traditional reinforcement model of the governance of local stress concentration has been changed.4. Base on AAR standard and secondary development technolgy, a fatigue life prediction software system embedded in the large-scale finite element analysis software- I-DEAS is developed for wagon body.