A general scenario of fish-eye crack initiation on the life of high-strength steels in the very high-cycle fatigue regime

摘要

When high-strength steels are subjected to very high-cycle fatigue loading, crack initiation site shifts from surfaces to the interior, and a fish-eye forms on the fracture surface. Majority of the fatigue life is estimated to be associated with the formation of this internal crack morphology. In the present work, features of such internal cracks in two high-strength steels are studied. Specifically, three initiation patterns are investigated. A general internal crack initiating scenario is proposed base on an understanding of dislocation slip in the materials. A simplified threshold is calculated from Young's modulus and interatomic spacing, defining the transition from the initiation stage to the crack propagation. The relationship between internal crack initiation and slower descending S-N curves is discussed.