Very-high-cycle fatigue (VHCF, the fatigue failure beyond 10⁷ cycles) of high-strength alloys is a new area of fatigue disciplinary and a challenge to the traditional fatigue limit at 10⁷ cycles. The components of airplanes, high-speed trains, etc. require the theory and methods of VHCF to ensure the safe performance up to 10¹¹ cycles.

This project proposed a new concept of crack initiation characteristic region in VHCF for high-strength alloys. The threshold value for this region is a function of Burgers vector and shear modulus of material. This region of tens of microns in diameter consumes more than 95% of total fatigue life. The crack initiation characteristic region was revealed to be a nanograin layer, and a model of Numerous Cyclic Pressing (NCP) was proposed to successively explain its formation mechanism.

This project established models of fatigue life and fatigue strength prediction for VHCF; proposed a model to explain the competition mechanism of VHCF crack initiation from surface or from interior in air and in corrosive environment, and revealed the new phenomenon of remarkable degradation of VHCF strength in corrosive environment for high-strength alloys.

Schematic and brief description of NCP model