Fatigue strength of welded structures is affected by welding residual stresses, which influence crack propagation at weld toe or root, considerably reducing the effectiveness of the structure and increasing 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 the local work hardening, introduction of compressive residual stresses and closing of notches at the weld toe. However, several aspects of this treatment need to be clarified or further investigated. Many researchers are focused on HFMI-treatment, simulating the impact of the peening tool at the weld toe. The present study focuses on the stability of compressive residual stresses introduced by HFMI-treatment when a cyclic load is applied on a gusset welded joint. Peening response of a flat stress-free-plate, under different peening process parameters is also investigated. Furthermore, comparisons of HFMI with other peening techniques are carried out to clarify which technique is the most reliable.

The validity of the present study is demonstrated by comparison with experimental residual stress measurements.

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