Improvement of loading ultrasonic peening on fatigue strength of welded joints under high stress ratio

Tubular Tjoints made by 20 steel were treated by loading ultrasonic peening. The test results were compared with aswelded joints and joints treated by unloading ultrasonic peening. The testing results show that, under the loading condition of high stress ratio R=0.75, the fatigue strength was increased by 23%, and the fatigue life was prolonged by 1.4 times after treated by unloading ultrasonic peening. After loading ultrasonic peening, the fatigue strength was increased by 70%, and the fatigue life was prolonged by 5.6~8.5 times. The difference for the fatigue performance was expounded from the microstructure on the surface, the hardness in the welded toe and the residual stress in the welded joints. The ABAQUS finite element analysis software was used to simulate the residual stress in the welded joints treated by loading ultrasonic peening and unloading ultrasonic peening. The results show that compared to joints treated by unloading ultrasonic peening, the surface compressive stress value and the stress depth for joints treated by loading ultrasonic peening were higher.