New approach for the correlation of fatigue crack growth in metals on the basis of the change in net-section strain energy

A new approach to correlate fatigue crack growth data of metals on the basis of the change in net-section strain energy is presented. Extensive experimental data, including some historically significant fatigue crack growth data, generated using center-cracked (CCT) and single-edge notched (SENT) tension specimens, are used to demonstrate this correlation. It is shown that this correlation, quite remarkably, is as strong as that based on the stress intensity factor range (ΔK) in fracture mechanics. The reason for this surprising similarity is explored using the analysis of the net-section stress increase in fracture mechanics specimens. It is found that the actual role of the finite-width-correction factor in fracture mechanics is to create the stress amplification effect on the finite specimen, having a given crack length, to produce the same K as that of an infinite specimen. The present work demonstrates that the phenomenon of fatigue crack growth can be easily understood on the basis of the accumulated change in net-section strain energy which directly relates to the accumulated work done at the loading ends, which determines the rate of fatigue crack growth. It is a simpler and a physical approach for the accurate description of fatigue crack growth behavior of metals. The approach simultaneously validates the use of fracture mechanics parameters (∆K) for fatigue crack growth, by providing the insight that the physical meaning of stress intensity factor is embedded in the change in the net-section strain energy.