Mechanized HFMI for improved fatigue life in complex weld shapes

Abstract

This study investigates the implementation of mechanized high-frequency mechanical impact (HFMI) treatments to enhance the fatigue life of complex welded structures. Digital visual inspection and path planning are utilized through digital laser scanning system to automate the HFMI process for more complex weld shapes in S355 steel grade, such as circular weld seams, which are more challenging to treat consistently. The mechanized HFMI setup was calibrated to ensure precise alignment and consistent application of the HFMI tool along the weld toe line. Finite element analysis was used to simulate the HFMI process, focusing on the effects of multi-pass HFMI treatments and optimizing treatment parameters. The simulations identified fatigue initiation sites which were confirmed with the mechanized HFMI treated specimens. Fatigue testing of both as-welded and HFMI-treated samples was conducted, revealing significant improvements in fatigue strength for the HFMI-treated specimens, which is in line with IIW recommendations. The fatigue test results were also compared with previous testing of manually treated samples. It was concluded that the fatigue life scatter, expressed in log C (load capacity), resulted in a smaller standard deviation for the mechanically HFMI-treated samples than the manually treated samples. Geometric measurements from laser scanning post-HFMI treatment also indicated reduced scatter in weld toe radius and HFMI groove depth compared to manual treatments, demonstrating the robustness and consistency of the mechanized process.