Crack behaviour after High Frequency Mechanical Impact treatment in welded S355 structural steel

Paper in proceeding, 2021

High-Frequency Mechanical Impact (HFMI) is a rather new post-weld-treatment method that has shown interesting fatigue life enhancement capabilities. The influence on material behaviour needs, however, to be investigated more to reach a full understanding and fully optimize the treatment, not least when the method is applied to existing welded structures. In this study, an experimental investigation was conducted to examine the effect of HFMI-treatment on crack behaviour in pre-fatigued welded details. A substantial reduction in crack width and a change in crack orientation were observed, both are believed to have beneficial effects in extending the remaining fatigue life. However, these beneficial effects decreased as the crack length increased. In light of the observations, a simplified phenomenological model was proposed to determine the crack opening after HFMI-treatment. In addition to that, finite element (FE) simulations were used to conduct several parametric studies. The conclusions from the FE study could be used to extend some of the IIW recommendations regarding the indenter inclination and the depth of indentation to cracked welds. Moreover, The FE simulations indicated that optimum results could be obtained if the indenter is placed and directed more towards the base metal than towards the weld.