Numerical Assessment Of Fatigue Property Of Welded Joint Improved By Ultrasonic Impact Treatment

The fatigue property of UIT-treated joint is different from welded joint.In order to evaluate the fatigue performance of treated joint,the software ABAQUS was used.The ultrasonic impact treatment process of T-joint was simulated,and two structural hot spot stress approaches: linear surface extrapolation(LSE)and through thickness at the weld toe(TTWT)were used to study the effect of material strength and plate thickness on fatigue property of UIT-treated joint.The results show that the structural hot spot stress approach based on through thickness at the weld toe(TTWT)method seem to be more effective and accurate to study the fatigue property of treated joints than linear surface extrapolation(LSE)method;The comparison between experimental data and numerical results indicates that the slopes of S-N curves for treated joints depend on material strength,and the adoption of S-N slope varying with yield strength is proven to be more proper for UIT improvement assessment;For UITtreated T-joints,the thickness correction exponents increase with material strength,whilst a reverse thickness effect is observed.The welding process of butt joint was simulated using sequence coupling method,and the welding residual stress field was obtained.The process of ultrasonic impact treatment was simulated on the basis of welding residual stress field.Subsequently,cyclic load was applied to the UIT-treated joint to study the law of stress relaxation under cyclic load.The results show that due to the modified local stress distribution around weld toe after HFMI treatment,the residual stress relaxation is limited to the first cycle under cyclic load,as the number of cycles increase,stress continues to release,but the degree of release is very small;Magnitude of the residual stress relaxation depends on the peak of cyclic load,the higher the peak of cyclic load is applied,the more relaxation of residual stress will be;Under cyclic loading with different stress ratios,when the cycle number is less,magnitude of the residual stress relaxation under stress ratio of R=0.1 is larger;As the number of cycles increase,magnitude of the residual stress relaxation under stress ratio of R=-1 is larger.