An investigation of the effects of stress ratio and crack closure on the micromechanisms of fatigue crack growth in Ti-6Al-4V
- Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering
The effects of positive stress ratios on the fatigue crack growth behavior of a forged, mill-annealed Ti-6Al-4V alloy (with duplex {alpha} + {beta} microstructure) are discussed. Differences between fatigue crack growth rates at low and high stress ratios are shown to be due largely to crack closure. A 1% offset procedure is shown to collapse closure corrected low stress ratio data with the closure-free high stress ratio data. A three parameter multiple regression model is developed for the prediction of the fatigue crack growth rate as a function of stress ratio, crack closure and stress intensity factor range for Ti-6Al-4V. The micromechanisms of fatigue crack growth in the near-threshold and Paris regimes are elucidated via crack tip transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Crack tip TEM shows that Stage II fatigue crack growth in Ti-6Al-4V is crystallographic in nature. Stage II cracks are shown to unzip along intersecting slip bands that are induced as a result of shear localization. The unzipping crack growth mechanism observed in polycrystalline Ti-6Al-4V is shown to be consistent with Neumann`s alternating slip model for the information of striations in single crystals.
- OSTI ID:
- 524536
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 7 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
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