PSI - Issue 68

M. Álvarez et al. / Procedia Structural Integrity 68 (2025) 272–278

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M. Álvarez et al. / Structural Integrity Procedia 00 (2025) 000–000

In this study, corrosion pits were considered as semi-elliptical defects, with an approximate pit depth in the range of 126-200 µm, and pit diameter between 350-720 µm. Pit size dimensions were estimated by means of Mitutoyo profilometer C-4500. 2.4. Corrosion-fatigue test conditions CF tests using precorroded S355G10+M specimens were performed at different axial load levels with σ max = 90%, 80%, 70% and 60%σ y , with artificial seawater and stress ratio R = 0.1. Fatigue testing frequency of 1 Hz was chosen, considering that frequencies up to 1.0 Hz should be appropriate regarding the evaluation of SN curves [Gkatzogiannis (2019)], to allow artificial seawater to penetrate the existing crack and locally corrode the material between each load cycle. Increasing the frequency in CF tests would discard the contribution of corrosion damage to the overall failure, and consequently the results from CF tests at high frequencies would be very similar to those results obtained from the fatigue tests in air [Mehmanparast (2021)]. ASTM G44-21 [American Society for Testing and Materials (2021)] was selected to set out conditions for the performance of alternate immersion corrosion tests in 3.5% NaCl aqueous solution. The alternate wetting test utilizes a 1 h cycle that includes a 10-minute period with the specimen receiving a 100 ml/min flow of artificial seawater, followed by a 50-minute period in absence of flow, during which the specimens are allowed to dry. This 1 h cycle was applied 24 h/day for the total number of cycles until failure. In-situ CF tests were conducted at room temperature on a servo-hydraulic machine, with the specimen surrounded by a plexiglass container to receive the artificial seawater flow during the wetting stage, as seen in Fig. 3 .

Fig. 3. In-situ corrosion-fatigue setup

3. Results and discussion 3.1. Post-mortem inspection after corrosion-fatigue tests After failure, specimens were observed in optical and scanning electron microscope (SEM), confirming in all cases that fracture occurred in the artificially generated pit, as observed in Fig. 4 .