Fatigue strength improvement of steel structures by high-frequency mechanical impact: proposed procedures and quality assurance guidelines

High-frequency mechanical impact (HFMI) has emerged as a reliable, effective, and user-friendly method for post-weld fatigue strength improvement technique for welded structures. During the past decade, 46 documents on HFMI technology for fatigue improvements have been presented within Commission XIII of the International Institute of Welding (IIW). This paper presents an overview of the lessons learned concerning appropriate HFMI procedures and quality assurance measures. Due to differences in HFMI tools and the wide variety of potential applications, certain details of proper treatment procedures and quantitative quality control measures are presented generally. Specific details should be documented in an HFMI procedure specification for each structure being treated. It is hoped that this guideline will provide a stimulus to researchers working in the field to test and constructively criticize the proposals made with the goal of developing international guidelines relevant to a variety of HFMI technologies and applicable to many industrial sectors. A companion document presents a fatigue design proposal for HFMI treatment of welded steel structures. The proposal is considered to apply to steel structures of plate thicknesses of 5 to 50 mm and for yield strengths ranging from 235 to 960 MPa. Stress assessment may be based on nominal stress, structural hot spot stress, or effective notch stress.