The Research Of Fatigue Property Of Welded Joint Treated By Ultrasonic Impact Under In-service Loading Condition

A new method - ultrasonic impact under in-service loading condition was proposed to extend the fatigue life of large structures and engineering components in-service. Besides that, the mechanism of improving the fatigue performance of welded joint was studied, for the purpose of providing a reference to optimize the process parameters.Contrast fatigue tests were carried out on T-shape tubular joints of 20 steel in three conditions: as welded, treated by ultrasonic impact treatment (UIT) and UIT under in-service loading condition. The result shows that: fatigue strength of 20 steel tubular joints under the condition of stress ratio R=0.75, fatigue life of specimens treated by UIT under in-service loading can be elongated by 12.2 times compared with that of as-welded specimens, and fatigue strength was enhanced by 5.6 times.Micro hardness test and microstructure of surface toe zone were observed , the results show that : hardness of specimens treated by UIT under in-service loading has been increased by 49.7% compared with that of as-welded specimens; and specimens treated by UIT was only 19.5%. Plastic deformation layer at the toe zone can be found in the UIT and UIT under in-service loading specimen. However, grain of the UIT specimen was much tinier than that of UIT in-service loading condition.ABAQUS finite element analysis software was used to simulate UIT under in-service loading process. After single shot of 3mm diameter at 10m/s impact the weld joints, the residual compressive stress was induced, and during the ultrasonic impact treatment under in-service loading process , surface compressive stress value is 80 MPa, the maximum compressive stress value is 380MPa at the position of 0.25mm off the surface, and the depth of compressive layer is 1.22mm.