@inproceedings{b67faf5f5e5c4d60894fb951e39593ed,
title = "Determining worst-case fatigue thresholds for grain-bridging ceramics",
abstract = "A method for determining worst-case cyclic fatigue thresholds in grain-bridging ceramics by quantifying the role of bridging is demonstrated for a model alumina. Crack-growth properties for both long and short (< 2 mm) cracks emanating from machined notches (root radii, ρ ∼ 15 - 150 μm) were investigated. When compared as a function of the applied stress-intensity range (ΔK), growth rates (da/dN) were far higher and fatigue thresholds ΔKTH were markedly lower with short cracks, with growth being observable at the lowest driving forces for short cracks emanating from razor micronotches (ρ ≈ 15 μm). For growth rates < 10-8 m/cycle, da/dN vs. ΔK data for short cracks merged with the steady-state data for long cracks after ∼2 mm of extension. This value corresponds well to the measured crack-bridging zone length for long fatigue cracks grown near ΔKTH. The crack-tip shielding contribution due to bridging was quantified using multi-cutting compliance and crack-opening profile techniques. Bridging stress-intensity factors were computed and subtracted from applied stress intensities to estimate an effective, near-tip driving force, ΔKeff. These results, in terms of ΔKeff, provided a lower threshold below which both long and short cracks are not observed to propagate and an estimate of the intrinsic toughness for the start of the R-curve. Such results quantitatively affirm that the reduced role of grain bridging is a primary source of the transient behavior of short cracks in grain-bridging alumina-based ceramics under cyclic loading. These methods are additionally applied to estimate the worst-case fatigue threshold and intrinsic toughness of a self-reinforced SiC based ceramic, for which direct testing at small crack sizes has been prohibitively difficult.",
keywords = "Alumina, Fatigue crack, Grain-bridging ceramics, Razor micronotches, Worst-case fatigue",
author = "Kruzic, {J. J.} and R. Yuan and Cannon, {R. M.} and Ritchie, {R. O.}",
year = "2003",
month = mar,
doi = "10.1002/9781118788035.ch7",
language = "English",
isbn = "9781118000427",
series = "TMS Annual Meeting",
publisher = "John Wiley & Sons",
pages = "61--68",
editor = "Liaw, {P.K. } and { Buchanan}, R.A. and D.L. Klarstrom and R.P. Wei and Harlow, {D.G. } and Tortorelli, {P.F. }",
booktitle = "Materials Lifetime Science & Engineering",
address = "United States",
note = "Materials Lifetime: Science and Engineering ; Conference date: 02-03-2003 Through 06-03-2003",
}