| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method for evaluating the fatigue fracture of a cylindrical metal material that is capable of not only surely reproducing a fatigue fracture occurring on the inner surface of a cylindrical metal material but simply evaluating fatigue characteristics of the inner surface of the cylindrical metal material with high accuracy. <P>SOLUTION: Characteristics of the fatigue fracture of a cylindrical metal material are evaluated in the following manner. First, a cylindrical test piece 1 is prepared in which the outer diameter of the center part 1b is set equal to or less than 90% of that of a restraint part 1a; the ratio of the outer to inner diameters of the center part 1b satisfies the relation of (outer diameter/inner diameter)≤2; and the thickness of the center part 1b is set equal to or greater than 1 mm. Second, a compressive residual stress equal to or greater than 25% of the tensile strength of the metal material is applied on the outer surface of the center part 1b and a compressive residual stress equal to or less than 2.5% of the tensile strength thereof is applied to a point 0.8 mm deep from the outer surface. Third, a fatigue fracture is caused on the inner surface of the cylindrical test piece 1 by applying a repeated bending or torsional load to the cylindrical test piece 1, and then the characteristics of the fatigue fracture of the cylindrical metal material are evaluated based on conditions of the repeated bending or torsional load under which the fatigue fracture occurs. <P>COPYRIGHT: (C)2012,JPO&INPIT |
