Improvement in fatigue design of marine propeller blades

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Improvement in fatigue design of marine propeller blades

Fukui, Y. / Sasaki, Y. / Moriya, K.

A study has been carried out concerning the design stress of marine propellers made of Mn bronze and Ni-Al bronze under the consideration of the fatigue strength at 10⁹ cycles. The fatigue strength up to 10⁸ cycles and the crack propagation characteristics of the materials were obtained in laboratory tests conducted on the same condition as full-scale propellers in service, and these test data were utilized in the study. The test data were analysed statistically and calculated with fracture mechanics. The S-N curve which is necessary for the fatigue design could be obtained through this procedure. The relation between the design stress and the design life, which is dependent on each kind of vessels and the degree of safety, was made clear by applying Miner's rule to the design S-N curve and a stress frequency distribution model which coincided well with the measured data on a vessel in service. It becomes possible for us to have the reasonable design stress through this study, if the stress frequency distributions would be obtained for each kind of vessels in various service conditions.