Short Fatigue Crack Growth in a Nickel-base Superalloy at Room and Elevated Temperature PDF Download
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Author: J. C. Healy
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Category : Materials
Languages : en
Pages :
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Author: J. C. Healy
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Category : Materials
Languages : en
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Author: J. Byrne
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Category : Materials
Languages : en
Pages :
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Author: James Finis McCarver
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Category : Nickel alloys
Languages : en
Pages : 200
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Author: Fernando Jorge Ventura Antunes
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Category :
Languages : en
Pages :
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Author: NE. Ashbaugh
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Category : Crack arrest
Languages : en
Pages : 11
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An experimental program was conducted to evaluate the effects of frequency and R on the near-threshold crack growth behavior of Inconel 718 at 649°C in laboratory air. Frequencies from 0.01 to 400 Hz and R from 0.1 to 0.9 were applied to compact tension [C(T)] and middle- or center-cracked tension [M(T)] specimens under decreasing-K conditions using computer-controlled test machines. Digital load-displacement data were obtained to determine crack length and closure load. The fatigue crack growth threshold in Inconel 718 at 649°C obtained using decreasing ?K testing was generally associated with a crack arrest phenomenon which could be attributed to the buildup of oxides with time. Over the ranges of R and v used in this investigation, the growth rate behavior at the onset of crack arrest appears to be a combination of time-dependent and cyclic-dependent behavior. Even at 400 Hz, purely cyclic behavior was apparently never reached. For crack growth rate modeling, both frequency and stress ratio have to be incorporated in the characterization of ?Kth. Over the ranges of parameters tested, a cyclic threshold was approached at high frequencies and low R and a sustained load time-dependent threshold was obtained at high R, indicating that the cyclic contribution to the growth rate was negligible.
Author: Sara Dalby
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Category :
Languages : en
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Author: S. Dalby
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Category : Materials
Languages : en
Pages :
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Author: John A. Newman
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Category : Fracture mechanics
Languages : en
Pages : 16
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Author: R. M. Pelloux
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Category :
Languages : en
Pages : 38
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Fatigue behavior of short cracks was studied in Inconel X-750, Inconel 718, Waspaloy and PM-Rene 95. Crack growth rates were measured for crack lengths from 50 microns to 2mm. Three regimes of behavior were generally observed: 1) an initiation regime in which crack propagation rates are nearly zero; 2) a short crack regime in which crack propagation rates increase slowly and variably with crack length but with propagation rates higher than would be predicted by LEFM in the near-threshold regime; and 3) a long crack regime in which conventional fracture mechanics is applicable. The threshold criterion and crack propagation rates for short cracks are shown to be strongly dependent on the stress ratio. Negative stress ratios promotes rapid crack initiation. This behavior is confirmed theoretically by a Dugdale model which establishes a criterion for crack extension based on the accumulation of plastic work in the crack tip plastic zone. Fractographic investigations show that short cracks propagate in a transgranular-crystallographic mode following a zig-zag path which is macroscopically perpendicular to the applied stress. An experimental technique was developed to generate small eliptical crack initiation sites using a pulsed Nd-YAG laser. An AC potential drop system for continuous and automated measurements of crack length at elevated temperature has been assembled.
Author: D. W. Hunt
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Category : Materials
Languages : en
Pages :
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