Fatigue crack growth in miniature specimens: The equivalence of Delta K-correlation and that based on the change in net-section strain energy density

In fatigue crack growth experiments of miniature specimens of Ti-6Al-4V alloy, it is shown that the stress intensity factor range ( Delta K) cannot uniquely correlate the crack growth rates based on the standard stress intensity factor solution, but can only on the basis of the solution for uniformly displaced ends. It also is shown that, remarkably, a similar and strong correlation exists between the change in the net section strain energy amplitude and the rate of fatigue crack growth. The proposed approach is direct and simpler and it throws a new light on the nature of driving force for fatigue crack growth in structural materials.