A study on the fatigue life due to the effects of residual stress and post welding process of SM490A specimens for railroad vehicle structure

초록

As speed of railroad vehicles increases, structures of bogie and chassis become lighter. Therefore, fatigue life evaluation is one of the challenging problems. In case of bogie frame of vehicle, it is a major structure that supports the load with chassis and it requires long life above 25 years. But bogie frame is manufactured by welding and many cracks and fractures are occurring at these points. So fatigue design criterion is required and Germany [1], Japan [2], U.S.A. [3] etc have self-regulation for fatigue design. In Korea, the major structures for railroad vehicle can endure repeated loads of two millions cycles as allowed stress. But this design criterion may differ from actual situation. A study that survey fatigue characteristic under repeated load using specimens by same material, same welding method with actual railroad vehicle structure is required at this point. A lot of study on the effect of weld zone profiles and weld details on fatigue [4-7] has been performed and many phenomena were explained. As for the effect of residual stress, some results explain the effect of welding residual stresses on fatigue life is significant. On the other hand, other conclusions seem to be mainly concerned with post welding process, like as grooving of weld zone on fatigue test specimens. Therefore, we studied that the effects of residual stresses and post welding process on fatigue life of specimen using SM490A material, which is same material used for bogie and chassis of railroad vehicle.