Effect of UIT on Fatigue Life in Web-Gusset Welded Joints

Ultrasonic impact treatment (UIT), which is a peening method, is usually used as a post-weld treatment in order to improve the fatigue strength of welded joints. In this study, fatigue tests were carried out on web-gusset welded joints treated by UIT and the results were compared with the fatigue lives of as-welded joints in order to examine the effects of UIT on the fatigue lives of welded joints. The fatigue lives of web-gusset welded joints treated by UIT increased to more than ten times those of as-welded joints. The introduction of compressive residual stress, relaxation of stress concentration at a weld toe, and refinement of grains under the weld toes were considered as possible reasons for the improvement in fatigue life caused by UIT. Residual stress near weld toes was measured using the X-ray diffraction method. The stress concentration factor at the weld toes was analyzed using the finite element method (FEM). The grain size under the weld toes was measured using electron backscatter diffraction pattern (EBSD) analysis.