PSI - Issue 79

Christoph Bleicher et al. / Procedia Structural Integrity 79 (2026) 239–247

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Before the fatigue tests started, the specimens were pre-corroded in seawater for 2 weeks according to recommen dations of DNV to enhance the corrosive effect. A comparison of a fatigue specimen with and without pre-corrosion is given in Fig. 2. The changes in surface color can be seen due to the corrosive effect of seawater. During pre-corrosion the threads of each specimen were covered to prevent early failure in the clamping due to the pre-corrosion. For the fatigue tests under seawater, a chamber was used to keep the seawater during the investigations around the specimen. To meet the requirements for fatigue testing according the DNV certification standard DNV-CG-0039 (2021) standardized seawater according to ASTM D1141-98 (2013) was used. The seawater was circulated during the test with 100 ml/min. With the help of a small pump, the sea water was brought into contact with the ambient air to make the test environment comparable to the operating environment for propellers.

Fig. 2: Upper: Fatigue specimen; lower: Fatigue specimen without (upper) and with pre-corrosion (lower).

Fig. 3: Fatigue test setup.

The fatigue tests under ambient air were performed at test frequencies of 5 to 105 Hz depending on the stress level to prevent a heating of the specimens at higher stress amplitude levels. For the fatigue investigations under seawater the test frequency was kept at 15 Hz based on discussions with DNV. The low test frequency assures a corrosion effect for all specimens since corrosion is mainly driven by time.