Issue 43

P. Zampieri et alii, Frattura ed Integrità Strutturale, 43 (2018) 90-96; DOI: 10.3221/IGF-ESIS.43.06 94 F ATIGUE TESTS atigue tests were conducted using a MTS810 hydraulic test system with a load capacity of 250kN (Fig. 4 a). Stress cycles were performed setting a sinusoidal load control signal (constant amplitude, R=0, 5 Hz frequency). All fatigue tests were made at room temperature. Two sets of samples were tested: set A composed of 8 uncorroded specimens and set B composed of 10 corroded specimens (Fig. 4 b). The results obtained from fatigue tests for both sets in terms of stress range Δσ and number of cycles to failure N were reported in a bi-logarithmic chart and interpolated by a regression curve calculated by the least squares method. In addition, the S-N curve with Ps (probability of survival) 97.7%, 10% and 90% were computed by Student’s distribution. The expression used for the S-N curve provided by the EC3 [15] is shown below: 6 2 10 k k R R R C N        (1) where k is the inverse slope of the S-N curve, Δσ C is the stress range at 2 million cycles of the detail category, Δσ R is the stress range (independent variable) and N R is the number of cycles (dependent variable). In Fig. 5 the data obtained from fatigue tests on uncorroded specimens and the corresponding S-N curves with Ps = 10%, 50%, 90% e 97.7% are reported. In Fig. 6 the data obtained from fatigue tests on corroded specimens and the corresponding S-N curves with Ps = 10%, 50%, 90% e 97.7% are shown. The two different S-N curves (Ps 97.7%) obtained from the experimental tests presented in this paper have about the same slope but the curve representative of corroded specimens moves downward respect to the curve of virgin samples. Figure 5 : Test results with Ps 10-50-90-97.7% of not corroded joints. Figure 6 : Test results with Ps 10-50-90-97.7% of corroded joints. 10 100 1000 1.00E+04 1.00E+05 1.00E+06 1.00E+07 Stress range [N/mm 2 ] Number of cycles Ps 50% Ps 97.7% Ps 10-90% 10 100 1000 1.00E+04 1.00E+05 1.00E+06 1.00E+07 Stress range [N/mm 2 ] Number of cycles Ps 50% Ps 97.7% Ps 10-90% F