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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

A Model of Nonlinear Fatigue-Creep (Dwell) Interactions

[+] Author and Article Information
Xijia Wu

Institute for Aerospace Research, National Research Council Canada, Ottawa, ON, K1A 0R6, Canada

J. Eng. Gas Turbines Power 131(3), 032101 (Feb 10, 2009) (6 pages) doi:10.1115/1.2982152 History: Received April 01, 2008; Revised April 02, 2008; Published February 10, 2009

A nonlinear creep/dwell interaction model is derived based on nucleation and propagation of a surface fatigue crack and its coalescence with creep/dwell damages (cavities or wedge cracks) along its path inside the material, which results in the total damage accumulation rate as given by da/dN=(1+(lc+lz)/λ){(da/dN)f+(da/dN)env}, where (da/dN)f is the pure fatigue crack growth rate, (da/dN)env is the environment-assisted crack growth rate, lc/lz is the cavity/wedge crack size, and λ is the average spacing between the internal cavities or cracks. Since wedge cracks are usually present in the form of dislocation pile-ups at low temperatures and cavitation usually occurs at high temperatures, the model attempts to reconcile the creep-/dwell-fatigue phenomena over a broad temperature range of engineering concern. In particular, the model has been used to explain the dwell fatigue of titanium alloys and high temperature creep-fatigue interactions in Ni-base superalloys under tensile cyclic creep rupture, compressive cyclic creep rupture, and tension/compression-hold strain controlled cyclic test conditions.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic of damage development in a specimen cross-section

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Figure 2

Comparison of Eq. 15 with the experimental data on IMI 834 (10): (a) normalized dwell-fatigue life as a function of dwell time and (b) S-N curves with different dwell times.

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Figure 3

Comparisons of Eqs. 18,19 with experimental data for Rene 80 at 871°C

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Figure 4

Comparisons of Eqs. 18,19 with experimental data for IN 100 (coated) at 1000°C

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