Extending the fatigue performance of new and repaired welded T-specimens using High Frequency Mechanical Impact

• Fatigue life of bent T-specimens with fillet welds; • Improvement of fatigue life of weldments by HFMI technology; • Application of HFMI technology on repaired welds; In this study, an experimental investigation was conducted to evaluate the benefit of high frequency mechanical impact (HFMI) on both newly welded and repaired steel joints. Welded specimens in the as-welded condition, identical specimens treated with HFMI, and HFMI-treated repaired welds were subjected to constant-amplitude cyclic loading until failure. The testing involved structural steel joints representative of typical bridge and shipbuilding details. HFMI treatment was applied along the weld toes using a standard pneumatic impact tool, and all specimens were tested under controlled laboratory conditions to record S–N (stress-life) data. HFMI-treated specimens, including both new and repaired welds, exhibited significantly improved fatigue resistance compared to their as-welded counterparts. Specifically, the HFMI-treated welds endured 2–3 times longer life than as-welded joints under equivalent loading. Additionally, the application of HFMI to repaired welds further extended their fatigue life, demonstrating that HFMI is not only effective in new structures but also offers substantial benefits for welded joint rehabilitation. The treated joints showed a notable increase in fatigue life and an improvement in the FAT class (allowable stress range at 2·10 6 cycles).