JPS6231297B

PURPOSE:To make possible the inspection of only the propeller vane range which has the possibility that defects of more than permissible defect sizes exist internally by forecasting whether the defect internally existing in the entire area of the propeller vane develops as a fatigue crack in the actual use or not. CONSTITUTION:The magnitude of fluctuating stresses to be exerted upon the pressure surface of propeller vanes for ships is calculated based on unsteady lifting surface theory, and the coefficient of the lower limit stress expansion of propeller vane material is measured empirically from the propagation rate of fatigue cracking. A method of destruction dynamically evalulating whether the defect exisiting internally in the propeller vane develops as a fatigue cracking as said defect as a starting point or not is adapted by these fluctuating stress values, the values of coefficient of the lower limit stress expansion, and the position and wall thickness of the propeller vane, whereby the maximum size (permissible defect size) of the defect sizes at which the fatigue cracking does not develop in each position of the propeller vane is analyzed. Ultrasonic flaw detection is then performed by limiting to the range where there is the possibility that the defects of the sizes larger than the permissible defect sizes exist internally.