PSI - Issue 79

Martin Sladký et al. / Procedia Structural Integrity 79 (2026) 421–432

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where ∆ λ denotes the normalized stress range. Each figure also includes the normalized design S–N curve, shown in red, defined by a normalized stress range of 1 at 2 × 10 6 cycles and a fixed slope of m = 5, as recommended by Hobbacher and Baumgartner (2024).

Nominal stress-based approach

0.1 4 6 9 Normalized stress range ∆ λ [-] ∆ λ P 50% = 2.016 T σ = 1:2.519 m= 5 0.2 0.4 0.6 1 2

CHS lap CHS fillet

CHS-Plate fillet S CHS-Plate fillet G RHS fillet OPB RHS fillet IPB Plate fillet T Ben Plate fillet T Ten Plate-RHS fillet Plate fillet L Best-fit S-N curve Design S-N curve

10 4

10 5

10 6

10 7

Fatigue life in cycles N [-]

Fig. 5. S–N data for the nominal stress-based approach, normalized to the corresponding FAT class, with white-filled markers denoting specimens excluded from the evaluation of parameters listed in the annotation box.

Hot-spot stress-based approach

9

6

CHS lap CHS fillet

1 Normalized stress range ∆ λ [-] ∆ λ P 50% = 2.236 T σ = 1:1.566 m= 5 2 4

CHS-Plate fillet S CHS-Plate fillet G RHS fillet OPB RHS fillet IPB Plate fillet T Ben Plate fillet T Ten Plate-RHS fillet Plate fillet L Best-fit S-N curve Design S-N curve

0.7

10 4

10 5

10 6

10 7

Fatigue life in cycles N [-]

Fig. 6. S–N data for the hot-spot stress-based approach, normalized to the corresponding FAT class, with white-filled markers denoting specimens excluded from the evaluation of parameters listed in the annotation box.

The individual fatigue life estimation approaches were compared using parameters derived from the fitted S–N curves. The comparison parameters included the normalized stress range at 10 6 cycles, ∆ λ P 50% , indicating the average