The effects of ultrasonic peening treatment on the ultra-long life fatigue behavior of welded joints

The conventional fatigue design codes was formulated based on the data from test stress cycles less than 1 × 107. Most of them could not be applied for welded structures serviced in the ultra-long life region so the new recommendations were discussed. The method of ultrasonic peening treatment (UPT) was introduced in this thesis as a post-weld treatment to improve the fatigue strength of the welded structures. The fatigue behavior of welded structures in the ultra-long life region was investigated using an ultrasonic fatigue test machine under two post-weld treatment states: the as-welded and the UPT. Discussion had also been made about the fracture mechanism on the UPT joints in ultra-long life fatigue test.