An investigation of the effects of stress ratio and crack closure on the micromechanisms of fatigue crack growth in Ti-6Al-4V

Journal Article · Tue Jul 01 00:00:00 EDT 1997 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(96)00380-1· OSTI ID:524536

Dubey, S; Soboyejo, A B.O.; Soboyejo, W O ^[1]

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1. 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, Vol. 45, Issue 7; Other Information: PBD: Jul 1997
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
FATIGUE
CRACK PROPAGATION
TITANIUM BASE ALLOYS
ALUMINIUM ALLOYS
VANADIUM ALLOYS
STRESSES
MATHEMATICAL MODELS
REGRESSION ANALYSIS
PREDICTION EQUATIONS
STRESS INTENSITY FACTORS
SLIP