Investigation on improving fatigue properties of welded joints by ultrasonic peening method

摘要

The fatigue strength of welded joints in welded structures is much lower than that of the base metals. Many experiments show that the fatigue crack normally initiates at the weld toe, so that the fatigue strength can be dramatically increased by peening the weld toe. Ultrasonic peening is one of the most useful methods to improve the fatigue behavior of welded joints by improving the weld toe geometry, removing weld toe defects and modifying the residual stresses distribution in this region. To evaluate the ultrasonic peening, fatigue tests were performed on butt and cruciform joints of Q235B steel both in the as-welded and peened conditions. Results show that joints showed a significant increase in fatigue life at different stress levels. The fatigue life of peened joints was significantly longer than that of the as-welded joints, and in many cases fatigue cracks initiated in the base metal instead of the weld toe.2. The increase in fatigue strength of the peened butt joints compared to the as-welded joints was 57%, and for the cruciform joints the increase was 64 ～ 71%. The fatigue strength of both types of joints was not lower than that of the base metal: Welded joints are no longer a critical location. TIG dressed joints were also tested for comparison with peened joints: in the high stress range TIG dressing was more effective, whereas in the lower stress range ultrasonic peening was more effective.