As can be seen from Fig. 14, we assumed that the initial damagevalue D is 0 before the test loading. As the number of loading cyclesincreases, the damage value D increases slowly, the slope of the curve increases, and the damage develops faster and faster. As the ratio of Nto Nf reaches 0.9 and 0.99, the the damage values D of the specimen areapproximately 0.4 and 0.8, respectively, which indicates that the fatiguecracks initiation and propagation process accounted for a verylarge proportion of the total fatigue life, in contrast, the transientfracture stage was not fully developed. As the number of loading cyclesapproached the total fatigue life, the damage value D increased rapidly,which shows the specimen developed a fast transient fracture.