A Guideline for Fatigue Strength Improvement of High Strength Steel Welded Structures Using High Frequency Mechanical Impact Treatment

In the past decade, high frequency mechanical impact (HFMI) has significantly developed as a reliable, effective and user- friendly method for post-weld fatigue strength improvement technique for welded structures. This paper presents a proposed fatigue design and assessment guideline for HFMI improved welded joints. Stress analysis methods based on nominal stress, structural hot spot stress and effective notch stress are discussed. The document especially considers the observed extra benefit that has been experimentally observed for HFMI treated high strength steels. The proposal is considered to apply to steel structures from plate thickness 5 to 50 mm and for yield strengths ranging from 235 MPa to 960 MPa. Several fatigue assessment examples are also provided. Lessons learned concerning appropriate HFMI procedures and quality assurance measures are presented. Due to differences in the HFMI tools and the wide variety of potential applications, certain details of a proper treatment procedures and quantitative quality control measures are presented generally. It is proposed that specific details should be documented in a HFMI Procedure Specification for each structure being treated. It is hoped that this guideline proposal will provide a stimulus to researchers working in the field.