PSI - Issue 75

Gary B. Marquis et al. / Procedia Structural Integrity 75 (2025) 530–537 Marquis, Barsoum & Leitner / Structural Integrity Procedia (2025)

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1. Introduction High-frequency mechanical impact (HFMI) treatment has been established as an effective post-weld improvement technique to enhance the fatigue strength of welded joints. Since the publication of the 2016 IIW HFMI recommendations [1], significant advancements in research and application have led to a 2024 update. The new recommendations clarify, expand, and improve various aspects of HFMI treatment, including material strength range, fatigue strength assessment, correction factors, and retrofitting applications. Figure 1 illustrates the basic principles of HFMI treatment and examples of welds after HFMI treatment.

Figure 1. Typical weld toe profile before and after HFMI treatment: a) original weld toe; b) high-strength steel indenter positioned at the toe; c) impact plastically deforms the material; d) modifies residual stresses and reduces local stress concentration geometry. HFMI has gained increasing attention due to its ability to extend the fatigue life of welded structures, particularly in high-strength steels used in construction, bridges. Based on these recommendations, other codes and standards have implemented HFMI as an acceptable post-wed treatment technique, e.g. the Eurocode 3 [2]. As fatigue failures are a major concern in welded structures, optimizing the post-weld treatment process is critical. The 2016 IIW HFMI recommendations provided foundational guidelines, but continuous research has indicated that modifications were necessary to accommodate higher-strength steels, improved assessment methods, and enhanced quality control measures. The 2024 update addresses these concerns by incorporating more precise correction factors, extending the applicability range of HFMI treatment, and providing standardized verification procedures for HFMI equipment [3]. The 2 nd edition of the IIW HFMI recommendations [4] is currently under revision and editing for publication in the IIW collection. 2. Recent Developments in HFMI Treatment Guidelines Several research studies confirm the veracity fatigue design aspects of the 2016 IIW recommendations [5][6][7]. However, the abundance of new research and test data demonstrated that certain portions of the 2016 recommendations need to be clarified, expanded, and improved. The key updates in the 2 nd edition 2024 IIW HFMI recommendations are: • Expanded material scope. The applicable range for HFMI treatment has been extended to steels with yield strengths up to 1300 MPa, compared to 960 MPa in the previous edition. This update supports the use of ultra-high-strength steels in modern lightweight and fatigue-critical structural applications. • Relaxed weld geometry requirements. The stringent geometric quality requirements for weld profiles prior to HFMI treatment (e.g., ISO 5817 Quality Level B [8]) have been eased. The updated guideline allows for treatment of welds that meet the fatigue strength criteria in the IIW recommendations [9],