舶用プロペラ翼の疲労破壊

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Fatigue failure in marine propeller blades of Ni-Al bronze was studied. i) First of all, the calculation of stress pattern and alternating stress imposed on propeller blades in service was carried out by the unsteady lifting surface theory. Results of the calculation indicate to be almost equal level in stress with that of actual measurements reported in the literature and therefore it is considered that the calculated results can be used for the study of fatigue behavior in propeller blades. ii) Fatigue test in sea water was carried out with large sized unnotched and notched (α=5.2, 9.7) specimens taken from actual propeller blades, and the fatigue life up to crack initiation was estimated with obtained fatigue curves and stress-frequency curve already known. It has been suggested, from the result of fatigue test, that there will be some possibilities of crack initiation within a year if very sharp flaw of α≥5.2 exists at the root of blade on the surface of pressure side under a probable stress-frequency. iii) Also fatigue crack propagation test was carried out in brine environment with W.O.L. type specimens taken from actual propeller blades, and fatigue life up to the failure after crack initiation was estimated on the actual broken propeller blade with a help of method of fracture mechanics. The formula of da/dN=3.37×10-14 (ΔK) 5.2 was obtained and the estimated fatigue life was 626 days. The formula showing the relationship between maximum allowable flaw size and alternating stress imposed on propeller blades was also obtained.
公益社団法人日本マリンエンジニアリング学会の論文

舶用プロペラ翼の疲労破壊

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