Evaluation Of Residual Welding Stresses And Fatigue Strength Assessment Of Welded Bogie Frame

The acceleration of railway transportation is inseparable from the development of bogie technology. The welded bogie frame, as the skeleton, bears vehicle and driving system and braking system and also isolates the vibration.Welded frame is a typical box girder structure with the large size and, complex welding seam. Since fatigue failure is the main failure mode of welded frame, the study of the fatigue behavior of welded frame and its influencing factors is the most important task in fatigue designing of welded frame.It should be noted that fatigue failure of welded structures is actually the fatigue failure of welded joint, because welding process itself can cause serious notch effect at the weld toe, combined with residual stress, welding defects and inhomogeneity of materials. Thereby increasing the fatigue life of welded frame also focus on such aspects.In the manufacturing process of welded frame, domestic vehicle factory still use traditional technique such as annealing to reduce the level of residual stress. However, foreign enterprises have adopted new technology by controlling welding residual stress and distortion to abandon post-weld heat treatment. Welding process can be optimized using computational welding simulation.Domestic railway equipment industry lacks depth study of the fatigue of welded structures. Meanwhile, there is urgent need for more practical and accurate method to solve fatigue problem of welded structures.The main work of this paper include:(1) Taking T-shaped weld joint as the research object, using thermal elastic-plastic finite element method to simulate its multi-pass welding process. The purposes is to get information of thermal field, welding residual stress and deformation and to optimize welding procedure in order to reduce residual stress. The numerical simulation results, however, deviate from the actual value. The next step is to find out the reasons of these deviation.(2) The fatigue strength assessment of large complex welded structures is in essence the fatigue assessment of welded joints. There are four available methods for evaluating fatigue strength of welded joints, i.e. nominal stress approach, hot spot stress approach, notch stress approach and fracture mechanics approach. The notch stress approach, which introduces virtual notch radius to reflect the notch effects of weld toe, can give more accurate results. Furthermore, it can normalize S-N curves of different joints. This paper assess fatigue strength of a certain type bogie frame using notch stress approach along with submodeling technology. The fatigue life prediction meets the design requirement.