Abstract: In order to research the fatigue behavior of the welded joints treated by ultrasonic peening under variable-amplitude load, the fatigue contrast tests of Q235B and 16Mn steel welded joints in two different states(ultrasonic peening and as welded condition)are directed. Test results show that：①When acted by variable amplitude load, contrasted with the Q235B steel specimen in as welded condition the fatigue strength of the specimen treated by ultrasonic peening is increased by about 69% and the fatigue life is prolonged by 5.7~19.0 times. ②When acted by variable amplitude load, contrasted with the specimen in as welded condition the fatigue strength of the specimen treated by ultrasonic peening is increased by about 80% and the fatigue life is prolonged by 2.5~17.0 times. ③Acted by variable amplitude load, the fatigue performance of the welded joints treated by ultrasonic peening or as welded is inferior to that of the welded joints which acted by constant amplitude loads. The fatigue life of the Q235B steel welded joints treated by ultrasonic peening is one third of that of the welded joints acted by constant amplitude loads. The fatigue life of as welded joints is about 70% of that of the welded joints acted by constant amplitude loads. The fatigue life of the 16Mn steel welded joints treated by ultrasonic peening is about one third of that of the welded joints acted by constant amplitude loads. The fatigue life of as welded joint is about 75% of that of the welded joints acted by constant amplitude loads. ④Fatigue strength of welded joints that treated by ultrasonic peening still maintains high when acted variable amplitude loading.

Key words: Fatigue performance, Ultrasonic peening, Variable amplitude load, Welded joints