PSI - Issue 66

0LORVODY .HSND -U et al. / Procedia Structural Integrity 66 (2024) 135–141 Miloslav Kepka Jr. et al / Structural Integrity Procedia 00 (2025) 000 – 000

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The working indenters are made of high-strength steel. In order to achieve a quality result, the indenters have different diameters and geometries. Examples of used indenters and a diagram of the HiFIT device for the application of the HFMI method, available at RTI, are shown in Fig. 1.

Fig. 1. HiFIT pneumatic gun and used indenters [https://www.hifit.de/en/products].

The HFMI method is suitable for both butt and fillet weld modifications and increases resistance to fatigue failures originating from the weld toe. The types of welds that are suitable for the use of HFMI are shown in Fig. 2.

Fig. 2. Examples of welds suitable for HFMI application [1].

According to the recommendations of the IIW = International Institute of Welding [1], there will be an increase in the contractual fatigue strength and a shift of the fatigue S-N curve towards a higher service life (to the category of a weld with a higher fatigue strength FAT). For steel with a yield strength lower than 355 MPa, the HFMI treatment will show an improvement of up to 4 FAT classes. For steels with a yield strength above 355 MPa, the application of HFMI leads to an improvement of one additional FAT class for every 200 MPa increase in yield strength (f y ), see Fig. 3 taken from [1]. For the calculation of the fatigue life, a slope of the S-N curves m = 5 instead of m = 3, as is usual for ordinary welds under harmonic stress without modifications, can also be considered.

Fig. 3. Maximum increase in the number of FAT classes as a function of f y [1].