Improvement factors for the design of welded joints subjected to high frequency mechanical impact treatment

The effectiveness of high frequency mechanical impact treatment for increasing the fatigue strength of welded structures has been investigated in several research projects over recent years. Based on extensive fatigue test data, design recommendations have been developed by different institutions. Most recommendations provide fatigue strength improvement factors that consider beneficial effects due to the application of post weld treatment methods. Current design recommendations use fatigue test data derived from small-scale specimens, but only very few studies have focused on welded joints with a plate thickness > 15 mm. This paper reviews existing design recommendations and provides a database for welded joints with a plate thickness exceeding those already covered. Butt-welded joints, longitudinal attachments and transverse attachments are covered in particular. Based on the data evaluated, improvement factors are given for a stress ratio of R = 0.1 for axial loading.