Effect of multiple weld repairs on fatigue strength of bogie frame of railroad vehicle

In the welded structure of railroad vehicles, the bogie frame requires a service life more than 25 years, cracks occur in the weld zone owing to the application of repetitive fatigue loading during operation. When cracks occur and propagate in the weld zone, they are removed through gouging, and gas metal arc welding is performed for repair. After the first weld repair, the second weld repair process is performed if crack is visible in the same area. In this study, the effects of repetitive repair welding on the fatigue characteristics were investigated using materials applied in railway vehicle structures. Three types of specimens (weld specimen, first weld repairs specimen, and second weld repairs specimen) were prepared, and fatigue and residual stress tests were performed. The results indicated that the weld specimen had the longest fatigue life, and the first weld repairs specimen had the shortest fatigue life. The fatigue life of the second weld repairs specimen was longer than that of the first weld repairs specimen. Residual stress tests and finite-element analysis results indicated that the first weld repairs specimen had the shortest fatigue life among the specimens tested, because the highest residual stress was generated.