Periods of Fatigue-Crack Propagation

It is important to stress that there is an initial time of fatigue when only a surface crack is initiated but the crack embryo cannot yet grow. It is preferable to term this time as an incubation period of fatigue. 

It is appropriate to divide the total number of cycles to the fatigue fracture Nf into three terms  

The higher the amplitude of alternating stress the smaller the critical crack size. At large Njncub Ngj. With this condition the initiation of a crack is a very 

We have derived [83] the equation for the length of the fatigue-crack embryo. 

E - the curve of fracture for the Ti + 6AI + 4V alloy, test data [87] D - calculated values of T incub for the same alloy. 

---