Fatigue performance of repair-welded and HFMI-treated transverse stiffeners

Large portions of infrastructure buildings, for example, highway and railway bridges, are steel constructions and reach the end of their service life due to an increase of traffic volume. Repair welding can restore the current welded constructional detail with a similar fatigue strength. However, due to the increase of fatigue loading (traffic), an increase of fatigue strength is needed in such bridge structures. For this reason, the combination of repair welding and high-frequency mechanical impact (HFMI) treatment was investigated in this study in order to quantify the increase of fatigue life by combining both methods. For this, transverse stiffeners made of steel grade S355J2 + N were subjected to fatigue loading until a pre-determined crack depth was reached. The cracks were detected by non-destructive testing methods. Weld repair was realized by removing the material containing the crack and re-welded by a gas metal arc welding (GMAW) process, following that post weld treated was applied by HFMI-treatment and the specimens were subjected to fatigue loading again. Hardness profiles, weld geometries, and residual stress states were investigated for both the original and the repaired condition. In the repaired condition without additional HFMI treatment, a similar fatigue life than in the original condition is observed for the specimens. The repair-welded and HFMI-treated specimens reach a significant higher fatigue life compared to the repaired ones in the as-welded condition.