Robustness of the HFMI techniques and the effect of weld quality on the fatigue life improvement of welded joints
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RESEARCH PAPER
Robustness of the HFMI techniques and the effect of weld quality on the fatigue life improvement of welded joints R. Aldén 1 & Z. Barsoum 2
&
T. Vouristo 1 & M. Al-Emrani 3
Received: 5 October 2019 / Accepted: 28 July 2020 # The Author(s) 2020
Abstract Robustness of HFMI treatment in different weld qualities according to ISO 5817 was studied, and fatigue testing of the treated samples was carried out in order to investigate the effect of the weld quality prior treatment. The results show that HFMI-treated welds with weld quality level D shows fatigue life improvements that fall within the IIW recommendations for HFMI. No significant influence from the HFMI operator or HFMI equipment on the fatigue life was found. However, the scatter in fatigue testing results varied with HFMI operator and indicated that different HFMI operators could produce consistent treatment results. A considerable effect on fatigue life from HFMI tool radius was found, where the 2-mm tool radius showed considerably greater fatigue life compared with the 1.5-mm tool radius. According to IIW (Marquis and Barsoum 2016), for steel grade SY = 700 MPa, the fatigue strength recommendation is FAT 160 (m = 5) for transverse stiffener–welded joints with as-welded quality B according to ISO 5817 (ISO/TC 44/SC 10 2011), prior to treatment. It can be observed in the current study that fatigue-tested HFMItreated welded joints, welded with weld quality D, are in good agreement with the IIW recommendations. Keywords Welded joints . Fatigue . HFMI . Improvement techniques . Weld quality
1 Introduction 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. In 2016, IIW published recommendation for HFMI treatment for improving fatigue strength of welded joints [1]. These recommendations give detailed guidelines on procedure, quality control, and fatigue strength improvement for a large range of structural steels, 235–950 MPa in yield strength, with approximately 12.5% increase in fatigue strength for each 200MPa increase in yield strength. The beneficial effect is mainly because of the impacted energy per indentation. The impacted
Recommended for publication by Commission XIII - Fatigue of Welded Components and Structures * Z. Barsoum [email protected] 1
SWERIM, Kista, Sweden
2
KTH Royal Institute of Technology, Stockholm, Sweden
3
Chalmers University of Technology, Göteborg, Sweden
material is highly plastically deformed causing changes in the material microstructure and the local geometry as well as high compressive residual stresses, in the close region of the yield stress of the material. In 2013, IIW published a collective recommendation for improving the fatigue strength of welded joints sensitive for weld toe cracking [2]. This gives detailed guidelines for procedures; quality assurance of treatment; and expected fatigue strength improvement for burr grinding, TIG dressing, and hammer and needle peening. Howe
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