PSI - Issue 38

Robin Hauteville et al. / Procedia Structural Integrity 38 (2022) 507–518 Robin Hauteville, Xavier Hermite, Fabien Lefebvre / Structural Integrity Procedia 00 (2021) 000 – 000

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6. Experimental results and median S-N curve As an example, this methodology is applied on a dataset following these steps of analysis: • Grubbs ’ test: 2 points were deemed statistically outlier for a 90% confidence level, • Bartlett's test: test is done for a 90% confidence level → Test is validated, • Median S-N curves obtained by including runouts data for Basquin, Stromeyer and Bastenaire models, • Fisher-Snedecor test is done for the 3 models → Test is validated, • Design curves for these 3 models are plotted. In the Figure 5, the two outliers are identified but kept for the analysis because none fracture analysis was carried out yet to justify their rejection. The three median S-N curves are plotting on this figure, and all are consistent for this case. Basquin model seems to be more conservative than the other models due to its no-asymptotic behaviour and gives a lower endurance limit at 2 million cycles based on the Table 1. Stromeyer and Bastenaire models are quite equivalent regarding endurance limit values at 2 million cycles. However, for the fatigue limit (E parameter) Stromeyer gives a lower value than Bastenaire and this is may be due to the high C value but its fitting with dataset seems to be good. A more advanced analysis should be necessary to determine which model is more adapted for this dataset. For each model, the design curve for a confidence level of 90% and the probabilities of survival of 90% and 99% are plotted in the Figure 6, the Figure 7 and the Figure 8.

Table 1: Endurance and fatigue limits for Basquin, Stromeyer and Bastenaire models Basquin Stromeyer

Bastenaire

Endurance limit at 2.10 6 cycles (MPa) (p=50%) Endurance limit at 2.10 6 cycles (MPa) (p=90%) Endurance limit at 2.10 6 cycles (MPa) (p=99%)

186.2 172.4 163.0

204.1 180.8 163.8 129.2

208.0 187.8 173.2 197.9

Fatigue limit (MPa)

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Figure 5: Outliers and Basquin, Bastenaire and Stromeyer model