Recent results on fatigue strength improvement of high-strength steel welded joints

Abstract

Economic considerations push technology towards new lightweight structural solutions. This results in great interest in using high-strength steels (HSS) for structural applications like in railway vehicles, bridges, offshore structure and high-speed ships. In all these applications, welding is the main joining method and fatigue of welds is the major design criterion despite the existence of locally deteriorated microstructure, increased stress concentration and unfavourable tensile residual stresses after welding. Good weld design is a must to ensure the structural durability and performance, however this does not guarantee lightweight design alone. Special applications, such as post-weld treatment methods, can be performed following the welding. Therefore, this study concerns about the recent developments on such improvement techniques by considering two most-commonly used fatigue strength improvement methods; high frequency mechanical impact (HFMI) treatment and tungsten inert gas (TIG) dressing. Evaluations based on more than 1500 fatigue data points extracted from the literature. Investigations include presentation of the individual data analyses and fatigue strength assessment of all the data points by the effective notch stress approach with the reference radius rref=1.00mm. The influence of material strength, residual stress state, weld toe profile and loading conditions on the fatigue strength improvement are all discussed.