PSI - Issue 79

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

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2.2. Cast samples Based on the recommendations of DNV (2021) and in cooperation with the classification society DNV, which surveilled the project “Bross”, a casting geometry with a relevant wall thickness of 40 mm was defined referring to a typical cooling condition and wall thickness of large ship propellers in the direction of the component’s tip. This geometry was used for different production batches from which “Batch 1”, “Batch 2” and “Batch 7” were finally investigated. The round bars as a wrought material for the latter manufacturing of fatigue specimens were removed in relation to a pre-defined withdrawal plan. The feeding system was designed in a way that the areas relevant for the fatigue specimens are not affected by shrinkages during the solidification of the batch. Moreover, the feeding system and thus the filling process has a decisive influence on components quality. A turbulent filling process causes non-metallic inclusions through mold material erosion and supports the formation of oxidic impurities. This has been avoided by simulating the casting process beforehand and by the development of a casting system enabling a smooth filling of the mold. After cooling, the cast samples were cut, the position of the fatigue specimen is marked and specimens of each batch were separated and prepared for subsequent material analysis, Fig. 1. Also, tensile specimens were removed from separately cast samples being cast parallel to the 40 mm samples. The results from the tensile tests are listed in Table 2.

Fig. 1. Left: Design of the mold with casting, gating and feeding system; right: Raw cast samples with marked specimen positions and designa tion (first number = number of batch, second number = number of plate, third number = number of specimen within one plate).

Table 2: Mechanical properties derived for the investigated casting in com parison to regulations from IACS (2023). R m [MPa] R p0.2 [MPa] A [%] Samples with 40 mm 682 288 19 IACS W24 recommendation > 590 > 245 > 16

3. Fatigue investigations The cyclic material behavior was determined with the help of stress-controlled fatigue investigations with the fa tigue specimens given in Fig. 2. All fatigue tests were conducted at room temperature. While the tensile tests were only conducted in air, the fatigue investigations were done under air and in seawater both under tensile, R σ = 0, and alternating loading, R σ = -1. Nonetheless, the main load cases and also the design process refers to the fatigue behavior under alternating loading, (DNV 2021). So, the focus of the presented fatigue investigations is given to this load ratio as well. Over the service life of a ship propeller, a maximum number of cycles of more than N = 1∙10 8 can be achieved. As such and in accordance to the guidelines (DNV 2021), the fatigue tests were performed until the limit number of cycles N lim = 1∙10 8 . The stress-controlled fatigue tests were conducted on servo-hydraulic test rigs with maximum load of 160 kN under constant amplitude loading, Fig. 3.