EFFECT OF MEAN STRESS ON FATIGUE PERFORMANCE OF WELDED JOINTS TREATED BY UPT

The fatigue contrast tests of unload longitudinal direction corner joints as original welded and treated by ultrasonic peening of Q235B in various stress ratio are directed. The improvements of fatigue performance of unload longitudinal direction corner joints resulted by ultrasonic peening are studied. The effect pattern of stress ratio on fatigue performance of welded joints that are treated by ultrasonic peening is studied. As tests results indicate that: ① In the condition of stress ratio R=-1, the fatigue strength of specimen treated by ultrasonic peening is increased by 165% of that of the original welded specimen. And the fatigue life of specimen treated by ultrasonic peening is as much as 75-210 times of that of the latter. When R=0.1, the fatigue strength is increased by 87% and the fatigue life is extended by 21-29 times. When R=-0.5, the fatigue strength is increased by 123% and the fatigue life is extended by 42-59 times. When R=0.45, the fatigue strength is increased by 51% and the fatigue