Probabilistic Life of DA718 for Aircraft Engine Disks

Deyber, S.; Alexandre, Franck; Vaissaud, J.; Pineau, A.

doi:10.7449/2005/superalloys_2005_97_110

Cited by 14 publications

(9 citation statements)

References 13 publications

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“…It should be added that in many cases it has been observed that the fatigue cracks can be initiated at bulge-like features formed by volume expansion of oxidising NbTi (CN) particles [154,155]. It is easily understood that this situation implies a size effect: the fatigue life is a decreasing function of component size as shown by Deyber et al [156].…”

Section: Microstructural Degradation Due To Surface Oxidationmentioning

confidence: 96%

Failure of metals II: Fatigue

Pineau¹,

McDowell²,

Busso³

et al. 2016

Acta Materialia

254

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Section: Microstructural Degradation Due To Surface Oxidationmentioning

confidence: 96%

Failure of metals II: Fatigue

Pineau¹,

McDowell²,

Busso³

et al. 2016

Acta Materialia

254

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“…Furthermore, fine grain microstructures (ASTM > 10) were demonstrated to be particularly sensitive to crack initiation when brittle surface or near-surface NMIs were present, especially at low temperatures [1,[4][5][6][7][8][9][10][11]. While NMIs in fine grain IN718 alloys are important in this cycling regime, other microstructural features such as coarse favorably oriented grains or twin boundaries can also play a key role in the crack initiation process [12][13][14][15]. At lower cyclic stress amplitudes, i.e.…”

Section: Introductionmentioning

confidence: 99%

Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Texier

Cormier

Villechaise

et al. 2016

Materials Science and Engineering: A

105

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Fatigue crack initiation in the direct aged version of the nickel-based superalloy Inconel 718 has been investigated at room temperature in the low stress/very high cycle regime via ultrasonic fatigue testing. Three different microstructures have been examined at the same strain amplitude in order to understand the influence of non-metallic inclusions (NMIs), i.e. carbides, carbonitrides and nitrides, and Σ3 twin boundary density on lifetime and failure mode. A slight refinement in grain structure and a higher Σ3 twin boundary density is associated with substantial reductions in lifetime. Decreasing Σ3 twin boundary density for fine grain microstructures results in a change in crack initiation mechanism from strain localization within grains at the high end of the grain size distribution to cracking of NMIs. To study the early stages of crack initiation and growth, specimens with pre-cracked NMIs were also tested in order to examine the role of the surrounding grain structure. Pre-cracked NMIs mainly result in macroscopic failure initiation at NMIs independent of the wrought microstructure. However, pre-loading specimens within the plastic domain highlighted the competition in crack initiation mode between cracked-NMIs and favorably oriented twin boundaries. Crack arrest from most of the pre-cracked NMIs demonstrates that surrounding grain structure (grain orientation, local plasticity and roughness in the vicinity of crack tip due to pre-straining) play a key role in the fatigue life of components stressed in the nominal elastic regime.

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“…However, crack initiation due to carbide or carbonitride are widely reported [9,11], and especially for fatigue tests on 718 Alloys.…”

Section: Discussionmentioning

confidence: 99%

Strain rate and temperature effects on crack initiation of direct aged 718 Alloy

Perrais

Burteau²,

Seror³

et al. 2014

MATEC Web of Conferences

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Abstract. During mechanical tests at high temperature in an oxidizing atmosphere, the effects of strain rate on crack initiation are noticeable. This effect is due to a coupling between local mechanical loading and oxidation. Samples were machined in a turbine disk made of direct aged alloy 718. Tests were performed to understand the effect of these couplings on crack initiation and to ensure lifetime is optimized. This study compared the cracking resistance of two different specimen geometries at a given plastic strain and performed quantitative measurement of the mechanical loading conditions inducing crack initiation between 600• C and 650• C. Sample geometries consisted in tensile flat specimens and V-shaped samples. This specific geometry was used to localize strain and damage in the apex of the V and to reach strain rates lower than those possible on standard specimens. Digital image correlation technique was used to provide strain measurements. For each temperature and strain rate, finite element calculations using the identified constitutive law were performed to get a refined level of strain in different areas at the V apex. Tests were stopped after an imposed displacement corresponding to a given plastic strain distribution. SEM observations of the surface of the flat tensile samples revealed no crack initiation. On the contrary, SEM observations at the apex of V specimens for which the level of cumulative strain was close to the level of cumulative strain of flat samples reveal the presence of intergranular damage when the strain rate used was below a given level.

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Probabilistic Life of DA718 for Aircraft Engine Disks

Cited by 14 publications

References 13 publications

Failure of metals II: Fatigue

Failure of metals II: Fatigue

Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Strain rate and temperature effects on crack initiation of direct aged 718 Alloy

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