Fatigue Life Enhancement of Fillet and Butt Welded Joints after Laser Peening

Laser peening which introduces compressive residual stresses on surfaces is effective in enhancing fatigue lives of welded components, because tensile residual stress due to welding is one of the most prominent factors reducing the fatigue lives. Structural steels are widely used for bridges, buildings, etc; however, the effects of laser peening on the structural steels are not well established, especially on the welded zones. In this study, the welded zones of a box-welded joint were treated by laser peening and the residual stress was examined. Moreover, fatigue lives were evaluated for box-welded joints and butt welded joints with and without laser peening. Results obtained are summarized as follows: (1) Laser peening resulted in a change in the residual stress from tensile to compressive around box welding zones of a fillet welded rib-plate. (2) Laser peening can dramatically extend the fatigue lives and increase the fatigue strength of fillet and butt welded joints.