Effect of load ratio and maximum stress intensity on the fatigue threshold in Ti-6Al-4V

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journal

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Original languageEnglish
Pages (from-to)129-147
Journal / PublicationEngineering Fracture Mechanics
Issue number2
Online published30 Nov 2000
Publication statusPublished - 1 Feb 2001
Externally publishedYes


There has been a renewed interest of late in the mechanisms responsible for the influence of the load ratio, R, and the maximum stress intensity, Kmax, on the threshold for fatigue-crack growth, ΔKth. While mechanistic explanations in the past have largely focused on the role of crack closure, it is certainly not the only mechanism by which Kmax influences ΔKth. In this work, we examine the effect of a wide range of loading frequencies (ν = 50-1000 Hz) and load ratios (R = 0.10-0.95) on fatigue-crack propagation and threshold behavior in a Ti-6Al-4V turbine blade alloy consisting of approximately 60 vol% primary-α and approximately 40 vol% lamellar α+β. The data presented in this paper indicate that at Kmax values above 6 MPa√m (> 0.5), where macroscopic crack closure is no longer detected in this alloy, ΔKth decreases approximately linearly with increasing Kmax. This result is discussed in terms of possible mechanistic explanations, including sustained-load cracking, microscopic near-tip closure, and static fracture modes, based on considerations of experimental evidence from both the current study and the literature.