PSI - Issue 66

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2025) 000 – 000 Available online at www.sciencedirect.com ^ĐŝĞŶĐĞ ŝƌĞĐƚ

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Procedia Structural Integrity 66 (2024) 135–141

8th International Conference on Crack Paths Improving Repair Welds with HFMI Miloslav Kepka Jr. a – Jiri Kepka a - Miloslav Kepka a, * a University of West Bohemia, Faculty of Mechanical Engineering, Regional Technological Institute, Univerzitni 2732/8, 301 00 Pilsen, Czech Republic

Abstract The HFMI (High Frequency Mechanical Impact) method proves to be a promising application for increasing the fatigue strength and service life of welded joints, made mainly of high-strength steels. In recent years, the IIW (International Institute of Welding) recommendation has been the subject of intensive experimental research at the Regional Technological Institute (RTI), a research center of the Faculty of Mechanical Engineering of the University of West Bohemia in Pilsen. The paper presents these results. It also evaluates the benefit of the HFMI method when applied to repair welds and recommends further research topics. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) 1. Introduction HFMI is a designation used for several technologies working on a similar principle. They differ in energy sources; some use ultrasonic piezoelectric elements or magnetostrictive elements and compressed air. HFMI is,, therefore,, a collective name for UIT – Ultrasonic Impact Treatment, UP – Ultrasonic Peening, UPT – Ultrasonic Peening Treatment, HiFIT – High Frequency Impact Treatment, PIT – Pneumatic Impact Treatment, UNP – Ultrasonic Needle Peening. The basic principle of all methods remains the same. A cylindrical indenter is accelerated against the part or structure at a high frequency (approximately 90 Hz). The acting force of the indenter should be in the order of kN. By applying the HFMI method, local changes are achieved in the microstructure of the material and in the local geometry of the weld, and compressive internal stress is introduced into the weld processing area and its immediate surroundings. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of CP 2024 Organizers Peer-review under responsibility of CP 2024 Organizers Keywords: repair welds; HFMI; laboratory tests; fatigue life;

* Corresponding author. Tel.: +420 604 831 035; fax: +420 377 631 112. E-mail address: kepkam@fst.zcu.cz

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of CP 2024 Organizers

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of CP 2024 Organizers 10.1016/j.prostr.2024.11.062