Fatigue crack growth discrepancies with stress ratio

This paper examines cracking in D6ac and 4340 steel along with Mil Annealed and STOA Ti–6Al–4V and finds that the data implies that in the Paris Region (Region II) of the crack growth curve there is only a minimal R ratio dependency. Presented is a theoretical basis for explaining this behaviour and suggest alternative ways for characterising crack growth prediction through the use of the Generalised Frost–Dugdale crack growth law. The Fatigue Damage Map method is then used to explain the physics behind this behaviour.