Abstract
UIT (Ultrasonic Impact Treatment) is the method to impact on weld toe with hard pins vibrated by ultrasonic energy, so that improving the weld toe prof ile and introducing compressive residual stress can be obtained. It is confirmed that UIT has high improving effect on fatigue strength of welded joints through many experimental researches. Those tests were conducted under low stress ratio and UIT was done in condition that specimens were not subjected to stress. When UIT me thod is applied to existing structure, its effect should be verified in condition that UIT is applied under loading and fatigue tests are performed under high stress ratio. In this study, the improvement effects have been examined under such conditions.
