Multiaxial fatigue limit for defective materials: mechanisms and experiments

Thomas, Benedict; Nadot, Y.; Bezine, G.

doi:10.1016/j.actamat.2004.05.006

Cited by 101 publications

(83 citation statements)

References 11 publications

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“…The ratio  shows indeed an increase with the defect size. This is coherent with the trends observed in the literature by Endo et al [18] and Billaudeau et al [19] on other steels and represented in Fig. 6.…”

Section: Results and Discussion Of The Fatigue Testssupporting

confidence: 82%

Competition between microstructure and defect in multiaxial high cycle fatigue

Morel¹,

Guerchais²,

Saintier³

2015

Frattura Ed Integrità Strutturale

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ABSTRACT. This study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect.

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Section: Results and Discussion Of The Fatigue Testssupporting

confidence: 82%

Competition between microstructure and defect in multiaxial high cycle fatigue

Morel¹,

Guerchais²,

Saintier³

2015

Frattura Ed Integrità Strutturale

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“…In total, four tensile and two torsion specimens were drawn from the bottom of the wedge and had artificial defects applied post heat-treatment. This technique of generating artificial defects has been qualified in other crack propagation investigations [19,22], and the size of these defects is presented in Table 3. A cross-section of a typical artificial defect is given in Figure 3(c).…”

Section: Materials Preparation and Microstructurementioning

confidence: 99%

Multiaxial Kitagawa analysis of A356-T6

Roy

Nadot

Nadot-Martin

et al. 2011

International Journal of Fatigue

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Experimental Kitagawa analysis has been performed on A356-T6 containing natural and artificial defects. Results are obtained with a load ratio of R = −1 for three different loadings: tension, torsion and combined tensiontorsion. The critical defect size determined is 400 ±100 µm in A356-T6 under multiaxial loading. Below this value, the microstructure governs the endurance limit mainly through Secondary Dendrite Arm Spacing (SDAS). . It is shown that the CDM and gradient methods are accurate; however fatigue data for three loading conditions is necessary to allow accurate identification of an endurance limit.

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“…(2b) shows the crack path of a crack, initiated at the tip of an artificial defect in a C 35 carbon steel. The conclusion of this study is that, fatigue mechanisms for the material containing artificial defects are similar to the defect free material; a micro-crack initiates from the tip of the defect in the maximum shear planes and is forced to propagate perpendicularly to the maximum principal stress direction due to the stress distribution around the defect (for more details see [13]). Consequently, it does not seem possible to conclude that materials with a defect, under fatigue loading, behave like brittle ones, a defect is not always equivalent to a crack and initiation can be similar to a defect free material.…”

Section: Fatigue Mechanisms In the Giga Cycle Regimementioning

confidence: 96%

“…Two materials have been fatigued close to the fatigue limit: a nodular cast iron containing natural defects and a C 35 carbon steel containing artificial defects. The two materials have been tested in many different conditions with a careful observation of damage at the tip of the defect, for different sizes and geometries of defects [10][11][12][13][14]. Fig.…”

Section: Fatigue Mechanisms In the Giga Cycle Regimementioning

confidence: 99%

Propagation Lifetime from the Surface and Internal Defects in the Ultra High Cycle Fatigue Regime~!2008-03-10~!2008-05-06~!2008-07-03~!

Nadot¹

2010

TOMSJ

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Ultra High Cycle fatigue leads to a failure initiated in the bulk material of a material. Some results on the nodular cast iron are presented: initiation occurs from the defects, located at the surface or in the bulk. It has been shown that environment plays a major role that could explain the difference between fatigue lives, for the surface and internal initiation. The influence of the defect size and crack growth law is discussed and, the importance of fatigue crack initiation stage is revealed, in the ultra high cycle regime

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Multiaxial fatigue limit for defective materials: mechanisms and experiments

Cited by 101 publications

References 11 publications

Competition between microstructure and defect in multiaxial high cycle fatigue

Competition between microstructure and defect in multiaxial high cycle fatigue

Multiaxial Kitagawa analysis of A356-T6

Propagation Lifetime from the Surface and Internal Defects in the Ultra High Cycle Fatigue Regime~!2008-03-10~!2008-05-06~!2008-07-03~!

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