Abstract
Marine propeller blades have been designed so far mainly with the object of obtaining higher propulsion efficiency. Meanwhile, fatigue failure of marine propeller blades lately has increased. The reason is thought to be that the recent tendency toward higher power for engines and higher speed for ships has increased the load on blades and the fatigue strength of propeller blades has become the critical point in their design. Accordingly, the establishment of fatigue design rules for marine propeller blades is necessary. For this purpose, the fatigue strength of blade materials must be determined. However, only a few data have been available on the fatigue strength of blade materials and most of those data have been obtained by rotating bending fatigue tests in which stress conditions differ greatly from those in full-size propeller blades. In general, fatigue strength is affected considerably by the stress conditions, so that those data are not sufficient to give a basis for fatigue design rules for marine propeller blades. From this point of view, fatigue tests and crack propagation tests were conducted on two kinds of propeller blade material, Ni·Al-bronze and Mn-bronze. The stress and environmental conditions of the tests were selected carefully to be close to those of full-size propellers in use. The effects of stress ratio, stress frequency and so on on the fatigue strength and the fatigue crack propagation characteristics of the blade materials were examined.
