PSI - Issue 75

Fritz Wegener et al. / Procedia Structural Integrity 75 (2025) 363–374 Wegener et al. / Structural Integrity Procedia 00 (2025) 000–000 3 Acc. to the 1 st Gen. of EC3, DC 50 applies for bolting assemblies subjected to normal stress and is to be understood as a lower limit. However, in the current revision FprEN 1993-1-9 (2024-02), the detail categories are considered in amore di ff erentiated way, see Figure 1 (b). In particular, the e ff ect of thread rolling and hot-dip galvanizing is taken into account by adjusting the DC. The size e ff ect is considered by means of a reduction factor for fatigue resistance k s , which leads to a reduction in the bearable direct stress range for d > 30 mm acc. to Equation 1 with n = 0 . 25. For hot-dip galvanized bolting assemblies, the exponent n was adjusted to n = 0 . 10 based on the findings of Glienke et al. (2021b) and Glienke et al. (2023). ∆ σ C , red =∆ σ C · k s =∆ σ C · 30 d n (1) 2.2. Fatigue strength assessment using the notch-strain approach The basis of the notch-strain approach is the comparison of the local stress and strain at the failure-critical location with the fatigue resistance determined for the base material. The fundamental applicability of the notch-strain ap proach to bolting assemblies has been intensively investigated in the past, see for example Marten (2009), Schneider (2010), Olveda et al. (2014) and Eichsta¨dt (2019). The individual elements of the notch-strain approach are shown in Figure 2.

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Fig. 2: Schematic diagram of the individual elements of the notch-strain approach in its application to bolting assemblies (a) Material behaviour; (b) Loading conditions; (c) Damage parameter; (d) Analytical S-N curve.

The basis for this is the determination of the cyclic stress-strain curve and the strain-life curve in strain-controlled material tests, see Figure 2 (a). The cyclic stress-strain curve can be described with the Ramberg-Osgood equation, see Equation 2, using the cyclic strain hardening coe ffi cient K ′ and cyclic strain hardening exponent n ′ according to Ramberg and Osgood (1943). The strain-life curve is described by the Co ffi n-Manson relation with fatigue strength