Abstract
The development of bending fatigue can be divided into the fatigue crack initiation stage and the crack growth stage, and the fatigue crack initiation life predominantly determines the total fatigue life. After a fatigue crack initiated on a power transmission element such as a gear, the crack will always grow until a fatigue break, so, none of fatigue break can be considered practically as none of fatigue crack initiation; and the bending fatigue strength can also be defined as the stress under that the fatigue crack will not initiate. The purpose of this research is to estimate bending fatigue strength based on the crack initiation. A practical method for the detection of a fatigue crack initiation using an ion-sputtered film was used in bending fatigue tests. The ratio of the fatigue crack initiation life among the total fatigue life was investigated. The ratios are clarified that increase with the decrease of bending stress, and reach the maximum value of 1.0 at the fatigue limit. The bending fatigue strength can be estimation based on the relationship between the relationship between the ratio and bending stress, and the appropriate number of load cycles to judge that the fatigue break will not happen can also be determined from the relationship between the ratio and fatigue life.
