According to the measured value of stress intensity factor, kmax and Kmin can be obtained, and the range of stress intensity factor Δ K can be calculated. The crack will only expand when it opens, but the compressive load will not make the crack expand. Therefore, the range of stress intensity factor has two cases. The fatigue life can be calculated according to the following formula.
When Δ K ≤ Δ kth, the crack will not propagate.
Where R is the stress ratio; Kmin and kmax are the minimum and maximum values of stress respectively; Δ K is the range of stress intensity factor; Δ kth is the important parameter of fatigue crack propagation; n is the number of cycles; AC is the initial crack size; A0 is the critical fracture size of crack; C and N are the basic parameters describing the fatigue crack propagation performance, which are determined by experiments.