PSI - Issue 28

4

Lucas F. R. C. da Silva et al./ Structural Integrity Procedia 00 (2019) 000–000

Lucas F.R.C. da Silva et al. / Procedia Structural Integrity 28 (2020) 1426–1430

1429

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After applying the transformation for R=0, with equation 1, it is possible to treat the experimental results under ASTM E739 statistical procedure. The statistical treatment consists of a linear regression aiming the evaluation of the mean S-N curves, and the respective confidence intervals as well as the statistical indicators, which indicates the quality of the regression. Curves for mean ± 3 standard deviation presents an interval of confidence of 99%. Figure 2 shows the S-N mean curve obtained for single snug tight bolt joints, the S-N mean ±3 standard deviations, multiple bolt joints with drilled and punched holes and reduced net section experimental data. Figure 2 also presents Eurocode 3 class 90, this class being suggested for bolted joints non preloaded fitted. For multiple bolt connection it was considered that the load distribution is 50 % for each bolt. The mean minus three times Standard Deviation S-N curves obtained from ASTM E379 for snug tight bolt joints shows a slope m=8.5, Δ = 114 MPa with the coefficient of determination R²=0.802.

Fig. 3. Experimental results according to ASTM E 379 for preloaded bolts

Figure 3 shows the mean S-N curve obtained for single preloaded bolted joints, the S-N mean ±3 standard deviation and the experimental data. Figure 3 also presents Eurocode 3 class 112, this class being suggested for bolted joints with preloaded bolts. The mean minus three times Standard Deviation S-N curves obtained from ASTM E379 for snug tight bolt joints shows an inclination m = 5.3, Δ = 108 MPa with the coefficient of determination R²=0.859. 4. Conclusion The experimental data obtained submitted to ASTM E739 procedure showed that Eurocode class 90 curve for fatigue design seems to be conservative for high cycle fatigue and unsafe for low cycle fatigue. This work evaluated a slope m=8.5 and Δ = 114 MPa for snug tight bolts under fatigue loading. Eurocode class 112 also seems to be conservative for high cycle fatigue projects. ASTM E739 procedure evaluated a slope m=5.3 and Δ = 108 MPa for preloaded bolts. Multiple bolts connection with drilled hole showed lower fatigue resistance than all the tested specimens. This result can be explained due to the poor quality of the drilling as can be seen on figure 4.