Evaluation of crack depth impact on HFMI-treated pre-fatigued welded bridge details

This study focuses on the utilization of high-frequency mechanical impact (HFMI) treatment for rehabilitating pre-fatigued steel bridge components. It incorporates time of flight diffraction (TOFD) for precise crack depth measurement, alongside strain range drop monitoring to enhance assessment accuracy. The experimental setup involves fillet weld specimens with cope hole geometry, using S355MC steel. The HFMI treatment process employs 3-mm diameter pins to achieve an HFMI indentation depth of 0.2 mm. The study demonstrated that HFMI treatment effectively extends the fatigue life of steel bridge components, showing significant improvements for cracks up to 1.2-mm deep. TOFD measurements, validated against manual optical measurements, consistently indicated crack depths within ± 0.1-mm accuracy. This precision is critical for assessing the HFMI treatment’s effectiveness in repairing pre-fatigued structures. The strain range drop method was used as a stop criterion to evaluate crack depth in real time, effectively reducing the number of TOFD measurements required during fatigue crack growth testing. The experimental results showed that HFMI treatment could improve fatigue life, moving specimens’ performance well above the IIW recommended FAT125 curve for treated steel details. In conclusion, this investigation confirms the significant potential of HFMI treatment for extending the life of pre-fatigued steel bridge components. The combined use of TOFD and strain range drop monitoring provides a robust framework for accurately assessing and optimizing HFMI treatment.