Mechanisms of Creep-Fatigue Interactions

Pineau, A.

doi:10.1007/978-94-009-2277-8_12

Cited by 17 publications

(7 citation statements)

References 32 publications

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“…(i) brittle cracking through thick oxide films or along grain boundaries contaminated with oxygen atoms [5,6], (ii) embrittlement due to sulphur atoms released by reactions between oxygen and metal sulphides [ 201, (iii) strain localisation in intergranular zones weakened by depletion of alloying elements due to their preferential oxidation [ 1,6], (iv) formation of voids or gas bubbles ahead of cracks due to vacancy injection associated with oxide growth or reaction between oxygen and carbides to produce carbon monoxide or dioxide [6,21,22], and (v) cavitation associated with formation of solid oxide particles or dissolution of metal carbides due to oxidation-induced depletion of alloying elements [ 6,221. It has also been suggested that intergranular cracking involving many of the above processes is promoted by a more inhomogeneous slip mode [4]. Previous studies of creep crack growth in Waspaloy indicate that the rate of cracking depends markedly on the microstructure and environment [ 231.…”

Section: Mechanisms Of Enhanced Crack Growth Due To Creep and Oxidationmentioning

confidence: 99%

Fatigue Crack Growth in Nickel‐based Superalloys at 500‐700°c. I: Waspaloy

Lynch

Radtke

Wicks

et al. 1994

Fatigue Fract Eng Mat Struct

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The effects of cyclic frequency, hold time, and stress-intensity-factor range ( A K ) on rates of fatigue crack growth in air at 500-700°C have been studied for Waspaloy-a nickel-based superalloy used for gas-turbine engine discs. The main effects observed were: (i) higher rates of crack growth for lower cyclic frequencies at high AK at 600 and 700°C. and (ii) lower rates of crack growth at low AK (and higher AK thresholds) for longer hold times at 7WC, compared with those at a baseline frequency of 2 Hz. Metallographic and fractographic observations suggested that the effects of cyclic frequency and hold time could be rationalised in terms of the competing effects of enhancement of cracking due to creep and inhibition of cracking caused by oxide-induced crack closure, fracture-surface-roughness induced crack closure, and crack-branching/deflection. Possible mechanisms for promoting intergranular and transgranular cracking at low cyclic frequencies or long hold times are discussed. NOMENCLATURE K = stress intensity factor dn/dt = crack growth rate per unit time AK =stress intensity factor range da/dN = crack growth rate per cycle AK, = threshold stress intensity factor range

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Section: Mechanisms Of Enhanced Crack Growth Due To Creep and Oxidationmentioning

confidence: 99%

Fatigue Crack Growth in Nickel‐based Superalloys at 500‐700°c. I: Waspaloy

Lynch

Radtke

Wicks

et al. 1994

Fatigue Fract Eng Mat Struct

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“…For cycling rates above this transition frequency, where there is minimal time for oxygen to diffuse along grain boundaries near the crack tip, the fracture surface is primarily transgranular, and the FCGR is slower . The transition frequency has been shown to depend on ΔK, temperature and microstructure, especially grain size . As the temperature drops below 650°C, the frequency of loading has to drop off significantly to continue to promote intergranular fracture and an acceleration of the crack growth rate .…”

Section: Introductionmentioning

confidence: 99%

Impact of compressive hold on out‐of‐phase thermomechanical fatigue crack growth in IN 718

Radzicki

Johnson

Neu

et al. 2017

Fatigue Fract Eng Mat Struct

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Accurate characterization and understanding of the fatigue crack growth behaviour of components in jet turbine engines is critical for successfully using a damage tolerant design method to maximise safety and efficiency. The hot section components experience changing loads and temperatures, and hence, fatigue crack growth rates are typically studied under thermomechanical loading. One question that remains unclear is the role of the compressive holds that are often part of an aircraft loading‐temperature spectrum. This experimental study was undertaken to investigate a turbine disk alloy, Inconel 718, subjected to different cycling and temperature profiles considering different lengths of hot compressive holds to determine its effect on the fatigue crack growth rate. It was found that the addition of a compressive hold at temperatures from 650 to 725 °C has no significant impact on the fatigue crack growth rate when compared with a cycle without a compressive hold. Fractographic analysis shows that crack growth is primarily transgranular in all cases studied suggesting that grain boundary oxidation, often observed during hot tensile holds, is insignificant.

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“…In the whole range between these two extremes, the failure process is usually termed creep-fatigue interaction (e.g. [6]). …”

Section: Introductionmentioning

confidence: 99%

Micromechanical Studies of Cyclic Creep Fracture Under Stress-Controlled Loading

Giessen

Tvergaard

1996

J. Phys. IV France

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Abstract. This paper deals with a study of intergranular failure by creep cavitation under stress-controlled cyclic loading conditions. Loading is assumed to be slow enough that diffusion and creep mechanisms (including grain boundary sliding) dominate, leading to intergranular creep fracture. This study is based on numerical unit cell analyses for a planar polycrystal model with the grains and grain boundaries modeled individually, in order to investigate the interactions between the mechanisms involved and t o account for the build-up of residual stress fields during cycling. The behaviour of a limiting case with a facet-size microcrack yields important insight for damage accumulation under balanced loading. Under unbalanced loading, the time-average accumulation of creep cavitation gives rise to macroscopic ratchetting, while its rate is demonstrated to depend subtly on material and loading conditions.

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Mechanisms of Creep-Fatigue Interactions

Cited by 17 publications

References 32 publications

Fatigue Crack Growth in Nickel‐based Superalloys at 500‐700°c. I: Waspaloy

Fatigue Crack Growth in Nickel‐based Superalloys at 500‐700°c. I: Waspaloy

Impact of compressive hold on out‐of‐phase thermomechanical fatigue crack growth in IN 718

Micromechanical Studies of Cyclic Creep Fracture Under Stress-Controlled Loading

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