Fatigue Strength Analysis Of The Welded Bogie Frame For Railway Vehicle

With the rapid development of high-speed railway in China, the speed of high speed train has been improved, the speed of CRH trains series has reached200～350km/h. Bogie is the main receiving components of the track excitation while vehicle is running, and bogie frame is the main bearing structure. Under the complex alternating load, the weld seam of the bogie frame can form fatigue crack extremely easily, which endangers the vehicle’s safety and reliability. Whether the fatigue strength of welded bogie frame can meet the design requirements will affect the high speed trains’running safety.Fatigue strength assessment method of welded structure includes nominal stress method, structural stress method, stress-strain method and fracture mechanics method. This paper expounds the principle and transition relationship of these methods. The former three methods have been widely used in engineering fatigue analysis, while fracture mechanics method is used for key parts of high security requirements due to its complexity. Equivalent structural stress method is one of the revolutionary achievements in the field of welded structure fatigue analysis in recent years, it is based on fracture mechanics and a large number of welding test, combined with the mesh-insensitive structure stress and the main S-N curve to predict the fatigue life of welded structure. This method’s mesh-insensitive is proved by lap joint and fillet joint which are modeled by shell element.This paper summarizes the research status quo of railway locomotive vehicle fatigue strength assessment, for the high speed bogie welded frame, the load cases of static strength and fatigue strength are determined by standards UIC615-4and EN13749. The static strength is evaluated by von Mises stress, and the multiaxial stress of fatigue strength load cases is transformed into uniaxial stress according to standard UIC510-5, the fatigue strength is evaluated by modified Goodman curve. At the same time, using the UIC615-4’s fatigue test load as design load, the load classification and dynamic stress distribution are obtained by finite element method. The fatigue life of the weld in the bogie frame is predicted by the equivalent structural stress method, using fatigue analysis software Fe-safe’s Verity module to calculate the structure stress of weld. In this paper, the fatigue strength of bogie welded frame is assessed by the method of fatigue limit based on the infinite life, the fatigue life of the weld is predicted by the equivalent structural stress method, combined with the equivalent structural stress’s main S-N curve and cumulative fatigue damage theory. So the results of two methods provide the basis for further structural design improvement on the handle so that the fatigue strength of welded frame is increased.