PSI - Issue 75

Florian Kalkowsky et al. / Procedia Structural Integrity 75 (2025) 581–592 Florian Kalkowsky et al. / Structural Integrity Procedia 00 (2019) 000 – 000 Δσ C,PS=50% = 45 N/mm² for test series IV and Δσ C,PS=95% = 70 N/mm² for test series VI were determined. As the 2 nd Eurocode generation didn’t consider the end distance 1 in the calculation of the DC the value of Δσ C = 35 N/mm² applies to both connection configurations, although the statistical evaluation of the tests showed a significantly different fatigue strength value. According to the authors, this was not only due to a difference in material strength. The fatigue resistances of the test series V and VII with Δσ C,PS=95% = 128 N/mm² respectively Δσ C,PS=95% = 140 N/mm² and the number of cycles until failure of the specimens were at a comparable level so that the insertion of an additional fastener did not lead to any significant change in fatigue resistance. As the components were made from the same batch of S355J2+N structural steel, only the notch effect would have been affected by the changed geometry, but this could not be determined from the results. Based on the directly comparison of the fatigue resistances for a variable slope parameter no increase could be found from test series I with Δσ C,PS=50% = 142 N/mm to test series V with Δσ C,PS=50% = 142 N/mm. But in general, the specimens from test series V showed high number of cycles until failure which once again confirms the increase in fatigue strength due to the higher material strength of the structural steel S355J2+N. Finally, the possible effect of the use of blind rivets as widely used fasteners in the field of lightweight steel structures was also to be investigated. Sleeve expanding blind rivets with nominal diameters of 6.4 mm and 10 mm were used for these connections. As a result of these investigations from test series VIII to X, the previously made observations from tests on bearing type connections with bolts could also be confirmed for connections with blind rivets as can be seen in Fig. 2 c). The fatigue resistance of the test series VIII with Δσ C,PS=95% = 105 N/mm² was comparable to these from test series IX with Δσ C,PS=95% = 106 N/mm². In all these series, ratios of the geometric parameters ( 1 and 2 ) to the hole diameter 0 were identical. These results therefore confirm once again that, despite the type of fastener, an identical notch effect was present in the connections, which dominated the fatigue strength of the components. The comparison with the DC’s according to current Eurocode 3 and 2 nd generation with DC 50 and DC 67 again shows a clear discrepancy for the test series with blind rivets. As with the connections with bolts, the use of the high-strength structural steel S500MC in test series X led to a significant increase in fatigue strength to Δσ C,PS=95% = 149 N/mm², which in turn almost corresponds to the ratio of the tensile strengths of the test materials from test series VIII and X when comparing the fatigue resistances. 3.3. Comparison of synthetic S-N curve based on FKM approach with fatigue test results In the previously shown evaluation of the test results compared to DC’s according to EN 1993-1-9 (2010) and the 2 nd generation FprEN 1993-1-9 (2024), a discrepancy could be identified for the majority of the test series. This discrepancy was attributed by the authors to an uncertain description of the notch effect and the dependence of the fatigue strength of the base material on material strength. The fatigue strength verification acc. to FKM-Guideline (2020) takes these important parameters into account as input parameters. Using the calculation method based on the FKM-Guideline (2020) for the fatigue strength verification with nominal stresses, the synthetic S-N curves type I shown in Fig. 3 were determined for all test series. 7

587

300 400 500

300 400 500

300 400 500

(b)

(a)

(c)

200

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200

108 157 135

124 169 165

118 158 120

140 156

50 Direct stress range Ds [N/mm²] 100

50 Direct stress range Ds [N/mm²] 100

50 Direct stress range Ds [N/mm²] 100

128 140

149 105 | 106

Fracture series VIII Run out series VIII P S = 95% m = 5 Synth. S-N Curve type I Fracture series IX P S = 95% m = 5 Synth. S-N Curve type I Fracture series X Run out series X P S = 95% m = 5 Synth. S-N Curve type I

Fracture series I Run out series I P S = 50% m = 5 Synth. S-N Curve type I Fracture series II P S = 50% m = 5 Synth. S-N Curve type I Fracture series III P S = 50% m = 5 Synth. S-N Curve type I

Fracture series IV P S = 50% m = 5 Synth. S-N Curve type I Fracture series V P S = 95% m = 5 Synth. S-N Curve type I Fracture series VI Run out series VI P S = 95% m = 5 Synth. S-N Curve type I

70

69

47

45

Fracture series VII P S = 95% m = 5 Synth. S-N Curve type I

20

20

20

10 4

10 5 Fatigue life N [-]

10 6 2×10 6

10 7

10 4

10 5 Fatigue life N [-]

10 6 2×10 6

10 7

10 4

10 5 Fatigue life N [-]

10 6 2×10 6

10 7

Fig. 3. Synthetic S-N curves type I of (a) Series I to III (b) Series IV to VII (c) Series VIII to X (d) with test results from fatigue tests