Improving Fatigue Strength of Welded Joints by Ultrasonic Impact Treatment

Enhancement in fatigue performance of welded joints by Ultrasonic Impact Treatment (UIT) was evaluated with large-scale rolled beam and built-up specimens having yield strength of 345 to 760 MPa. Eighteen rolled-beam specimens having welded details at cover plates and transverse stiffeners and eight built-up specimens having only transverse stiffener details were fatigue tested after treating the weld details by UIT. A partial factorial experiment design was carried out at various stress range levels between 52 and 201 MPa and at various levels of minimum stress, resulting in stress ratios not exceeding 0.6. Based on the test data fatigue design guidelines for AASHTO Category E ́ and Category C ́ details are proposed. UIT effectively elevated the fatigue limit without changing the slope of the S-N curve in the finite life region.