Issue 48

J. F. Barbosa et alii, Frattura ed Integrità Strutturale, 48 (2019) 400-410; DOI: 10.3221/IGF-ESIS.48.38 406 (HCF) the generalized Power Law curve presented a very pronounced degradation rate. The Kohout-Věchet model presented a coherent behaviour in the HCF region and are recommended to better indicate the fatigue limit of the material. Regarding the metallic material from Luiz bridge tested at R=-1 (fatigue test under strain-controlled conditions), which can be seen in Fig. 3, the fatigue curves for the Power Law and Logistic model obtained very similar performance. The differences between them becoming more evident only in number of cycles higher than 10 6 . In the low-cycle fatigue region, for the Power Law, Logistic and Kohout-Věchet curves a very similar adjustment is observed. A poor performance of the S-N curve obtained from the Kohout-Vechet model for numbers of cycles to failure between 10 5 and 10 6 is verified, improving estimates to values above 10 6 . By analyzing the adjustement of the curve of the ASTM standard to the experimental data in the LCF region, it is verified an increasing distances between the experimental data and predictions, and consequently increasing the MSE value, making this model with the largest mean square error. Figure 3 : Comparison of the S-N curves for the fatigue data of the metallic material from the Luiz I bridge, R=-1 ( fatigue test under strain-controlled conditions) . Figure 4: Comparison of the S-N curves for the fatigue data of the metallic material from the Trezói bridge, R=-1 ( fatigue test under strain-controlled conditions) . The available fatigue data from the material from the Trezoi Bridge consists on only 10 experimental points. Therefore, the conclusions to be obtained for the LCF and HCF regions are limited. Fig. 4 shows a marked difference in the fit of the analyzed S-N curves in the HCF region. The Power Law formulation obtained the lowest MSE (Tab. 1) followed by the Logistic model. These models achieved a good agreement with the experimental fatigue data above 10 6 cycles. The ASTM standard and Kohout-Věchet methods did not provided good estimates in the HCF region. However, it is not possible to 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 100 150 200 250 300 350 400 450 500 Max. Stress [MPa] N(Number Cycles) Logistic Kohout-Vechet Power Law ASTM E739 Exp. Data Luiz R=-1 10 2 10 3 10 4 10 5 10 6 100 200 300 400 500 Max. Stress [MPa] N(Number of Cycles) Logistic Kohout-Vechet Power Law ASTM E739 Exp. Data Trezoi R=-1