A practical analysis of residual stresses induced by high-frequency mechanical impact post-weld treatment

It is well known that fatigue strength of welded structures is affected by welding residual stresses. Residual stresses influence crack propagation at weld toe or root. This reduces the effectiveness of the structure and increases its construction and maintenance costs. A mechanical post-weld treatment such as HFMI (high-frequency mechanical impact) has been found to exhibit a significant fatigue life enhancement of welded joints. The effectiveness of this mechanical impact treatment is primarily based on the combination of three effects: improvement of local work hardening, introduction of compressive residual stresses, and closing of notches at the weld toe. However, residual stress relaxation under cyclic loading needs to be clarified or further investigated. This study focuses on establishing a practical analysis method of compressive residual stresses introduced by HFMI-treatment into a gusset welded joint. Stability of compressive stresses introduced by HFMI-treatment is investigated when cyclic loading is applied to the joint. The validity of the present study is demonstrated by comparison with experimental residual stress measurements available in the literature.