Region III, at high stress intensities, crack growth rates are extremely high and little fatigue life is involved.
This curve may be divided into three regions, which are discussed in the cyberlink powerdirector ultimate v13 crack following sections.
In this method, a component is designed such that if a crack forms, it will not grow to a critical size between specified inspection intervals.
The point of transition from Region II and Region III behavior is dependent on the yield strength of the material, stress intensity factor, and stress ratio.By the use of fracture mechanics principles it is possible to predict the number of cycles spent growing a crack to some specified length or to final failure.Various crack growth rate curves can be generated by varying the magnitude of the cyclic loading and/or the size of the initial crack.The crack growth rate accelerates as the maximum stress intensity factor approaches the fracture toughness of the material.Fatigue crack growth rate and the cycles-to-failure assuming a Safe-Life design approach.Crack growth rate is defined as crack extension per cycle, da/dN.If the plastic zone is sufficiently small that it is embedded within an elastic singularity zone, the stress intensity factor may still give a good indication of the stress environment at the crack tip.Although experimental verification of the existence of this threshold is difficult, Kth is usually shown to be between 5 and 15 ksi-in1/2 for steels and between 3 and 6 ksi-in1/2 for aluminum alloys.The Stress Intensity Factor module can be used to calculate values.Most of the current bentley azure repair manual applications of linear elastic fracture mechanics (lefm) concepts used to describe fatigue crack growth behavior are associated with Region.It is important to note that the fatigue-life estimation is strongly dependent on ai, crack bitdefender plus 2012 and is generally not sensitive to the final crack length, af (when ai value does not significantly affect the accuracy of the solution.Most structures operate in this region.Values of the exponent n can range from.0.0 with most values being between.0 and.0.

In many practical engineering situations this region may be ignored because it does not affect the total crack propagation life.
An example would be power trains that operate at very high speeds.
The crack length a is plotted versus the corresponding number of cycles N at which the crack was measured.