Abstract: Treated by ultrasonic peening or TIG dressing, the fatigue performance of welded joints and structures isto be improved significantly. This has been verified by many constant amplitude fatigue tests. Subjected to variableamplitude loads, the fatigue performance of the structures will be affected, so that the fatigue contrast tests of 16Mnsteel welded joints with fillet welds in three different conditions : TIG dressing, ultrasonic peening and as weldedcondition were performed. Test results indicated that : (1) Contrasted with the specimens in as welded condition thefatigue strength of the specimens treated by TIG-dressing is increased by about 37 % and the fatigue life is prolongedby 2.5 times when acted by constant amplitude load. When acted by variable amplitude load, contrasted with thespecimens in as welded condition the fatigue strength of the specimens treated by TIG dressing is increased by about34 % and the fatigue life is prolonged by 1.7～1.9 times. (2) When acted by constant amplitude load, contrastedwith the specimens in as welded condition the fatigue strength of the specimens treated by ultrasonic peening is increased by about 84 % and the fatigue life is prolonged by 3.5～27 times. But when acted by variable amplitudeload, contrasted with the specimen in as welded condition the fatigue strength of the specimens treated by ultrasonicpeening is increased by about 80 % and the fatigue life is prolonged by 2.5～17 times; (3) Whether acted by constant amplitude loads or by variable amplitude loads, in the low-medium stress level and medium-long life states theimprovement of fatigue strength of the welded joints created by ultrasonic peening is larger than that created by TIGdressing.

Key words: variable amplitude load, ultrasonic peening, TIG dressing, fatigue performanc e