Long life fatigue strength design method for metallic material
First Claim
1. A long-life fatigue strength design method for a mechanical part to be made of a metallic material, comprising:
- determining a functional relationship between a number of stress cycles to failure and a size of a trapped-hydrogen-affected area around a non-metallic inclusion in the metallic material, said determining of the functional relationship being based on a fatigue test performed on a portion of the metallic material;
determining an equivalent defect size, the equivalent defect size being a size of the non-metallic inclusion after growth corresponding to an assumed number of working stress cycles on a mechanical part to be made of the metallic material, said determining of the equivalent defect size being based on the determined functional relationship; and
designing the mechanical part by using the equivalent defect size in a calculation of an ultra-long life fatigue strength.
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Abstract
A long life fatigue strength design method for a metallic material is capable of allowing design of an optimum mechanical part according to a set service life by considering an increase in ODA (area affected by hydrogen observed blackish by a metallurgical microscope) size according to the assumed service life of the mechanical part. The method includes obtaining, from the results of a fatigue test, a functional relation between the number of stress cycles to failure and the size of a hydrogen affected area around an inclusion affected by trapped hydrogen. From the functional relation, equivalent defect sizes as the sizes of the inclusions after growth corresponding to the assumed number of cycles of working stress on the mechanical part using the metallic material are obtained, and the mechanical part is designed using the equivalent defect sizes in the calculation of a long life fatigue strength such as allowable stress, whereby a failure life design can be performed with the ODA size growth taken into account according to the assumed service life of the mechanical part.
18 Citations
10 Claims
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1. A long-life fatigue strength design method for a mechanical part to be made of a metallic material, comprising:
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determining a functional relationship between a number of stress cycles to failure and a size of a trapped-hydrogen-affected area around a non-metallic inclusion in the metallic material, said determining of the functional relationship being based on a fatigue test performed on a portion of the metallic material;
determining an equivalent defect size, the equivalent defect size being a size of the non-metallic inclusion after growth corresponding to an assumed number of working stress cycles on a mechanical part to be made of the metallic material, said determining of the equivalent defect size being based on the determined functional relationship; and
designing the mechanical part by using the equivalent defect size in a calculation of an ultra-long life fatigue strength. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification