PSI - Issue 79

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

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corrosion fatigue in seawater of around 95 MPa at N = 1·10 8 cycles for a wall thickness of 450 mm and of around 127 MPa for 25 mm wall thickness. Wenschot (1983) thus showed a wall thickness influence on fatigue but did not show further results for other process or component related parameters. Further fatigue strength values are given in Meigh (2000) for aluminum bronzes. The influence of corrosion under salt spray is also highlighted. However, there is a lack of precise information on alloy composition and a design spec ification for the use of these characteristic values in component design. There is also no information on the behavior of the materials under tensile loads. Results and a summary of findings on the corrosion behavior of aluminum bronzes can be found in Fleetwood (1970). However, it deals more with the pure corrosion behavior and less with superimposed mechanical stress and does not specify any fatigue strength values. The effect of microstructural discontinuities in CuAl bronzes was investigated by Sarkar (2015) and Chakrabarti (2014). There, a decrease in fatigue strength and an increase in scattering depending on the position and size of the defects were determined and the local defects were examined using X-ray computed tomography. These investigations are thus consistent with the experience gained in Bleicher (2017) for cast iron. Sarkar (2015), however, only assessed small castings with dimensions of 25x25x110 mm, which provide only limited comparable characteristic values for use in large ship propellers with wall thicknesses above 400 mm. The corrosion behavior or the superimposition of effects from the microstructure were not investigated. Bertoglio (2016) gives a nearly comprehensive overview over fatigue data under tensile and alternating loading done on aluminum bonze alloys in the recent decades and summarizes specific effects on fatigue strength like mean stresses and wall thicknesses by deriving influence factors. Moreover, data under different load ratios are recalculated to achieve a SN diagrams with all so far available fatigue data in literature for a comparison to DNV standards (DNV 2021). The result shows that experimental fatigue data from different sources are conservative related to international design standards. Moreover, Bertoglio (2016) summarizes design values for aluminum bronze alloys from literature and calculates slopes in the medium cycle fatigue regime as well as standard deviations for NiAlCu alloys both under air and corrosive media. It must be stated that in all investigations different chemical compositions of aluminum bronze alloys are investi gated. Moreover, mostly fatigue data are not sufficient for a good statistical evaluation due to a lack of magnitude of fatigue tests or superposition effects like wall thickness changes or defect situation. 2. Material 2.1. Chemical composition Main alloying elements in aluminum bronzes are aluminum, nickel, iron and manganese accompanied by zinc, tin, lead, silicon and sulfur. Every single element has a specific influence on the development of the final material proper ties. High attention needs to be paid to quantity of the main alloying elements as well as the purity from disturbing elements which might lead to negative effects on the microstructure and the mechanical properties. Specifications for aluminum bronze compositions are given by international standards like for example the IACS regulations (2023) and are summarized in Table 1. An excess of aluminum in the alloy leads to pure aluminum excretions from the supersat urated Cu-Al solid solution at the grain boundaries. Additionally, these precipitations influence the strength and cor rosion resistance while a significant excess of aluminum promotes the formation of brittle phases within the structure and has to be avoided.

Table 1: Chemical composition range for a CuAlNi - aluminum bronze (CU3) in accordance to IACS regulations (2023). Chemical composition (in %-weight) for Cu3 alloy Cu Al Ni Fe Mn Zn Sn 77 - 82 7.0 – 11.00 3.0 – 6.0 2.0 – 6.0 0.5 – 4.0 max. 1.0 max. 1.0