Very high cycle fatigue of high-strength steels: Crack initiation by FGA formation investigated at artificial defects

Spriestersbach, Daniel; Brodyanski, A.; Lösch, J.; Kopnarski, Michael; Kerscher, Eberhard

doi:10.1016/j.prostr.2016.06.141

Cited by 38 publications

(22 citation statements)

References 20 publications

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“…Figure 4(c) shows an example of this type of crack initiation site, which is difficult to analyze due to surface roughness in comparison with observations from past literature at 593°C and 20 Hz. [34] This rough area, also visible in Figure 4(a) and less obviously in Figure 4(b), could be assimilated to the fine granular area (FGA, also called optical dark area) observed during VHCF tests at R = À 1 that exceed 10 7 cycles on high-strength steels [35,36] and a titanium alloy. [37] In polycrystalline alloys, the FGA is generally defined by a rough area with a grain refinement.…”

Section: Resultsmentioning

confidence: 80%

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

Cervellon

Cormier

Mauget

et al. 2018

Metall Mater Trans A

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Section: Resultsmentioning

confidence: 80%

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

Cervellon

Cormier

Mauget

et al. 2018

Metall Mater Trans A

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“…The model proposed by Murakami seems, due to the fact that the hydrogen content of the investigated material will be very low after the heat treatment, not to be applicable to the results of the present study. In Spriestersbach et al showed the presence of a FGA around an artificial surface defect after VHCF failure in vacuum conditions and therewith clarifies that no hydrogen seems to be necessary for FGA formation. The model by Shiozawa et al discusses detachment of carbides as the root cause for FGA formation mainly based on investigations of 100Cr6 with ten times higher carbon content compared with the material tested in the present work.…”

Section: Resultsmentioning

confidence: 99%

Influence of mean stress and notches on the very high cycle fatigue behaviour and crack initiation of a low‐pressure steam turbine steel

Ritz

Beck

2017

Fatigue Fract Eng Mat Struct

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The aim of the present work is to investigate the influence of different stress concentration factors (1.09, 1.31, and 2.42) and several R‐values on the fatigue behaviour of martensitic steel X10CrNiMoV12‐2‐2 up to 2 · 109 load cycles at ambient temperature. The tests were performed using an ultrasonic fatigue testing system developed at the authors' institute. The S‐N curves of specimens with the lowest investigated stress concentration factor of 1.09 show for both R = −1 and R = 0.5 a flat slope with transition from surface to volume crack initiation at about 1–2 · 107 load cycles. The maximum number of load cycles where fracture occurs increases with increasing R‐value. The √area approach by Murakami describes lifetime behaviour within about 4 decades of lifetime and a wide range of load ratios. In case of internal crack initiation at R = −1, the fracture surface contains a fine granular area (FGA) around the inclusion within the typical “fish‐eye” fracture. With increasing notch factor, the fatigue strength up to 2 · 109 load cycles decreases and the slope of the S‐N curve becomes steeper in the low cycle fatigue and high cycle fatigue regime, especially for αk = 2.42. In this case, damage at internal defects is suppressed and fatigue cracks are generally initiated at the notch root.

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“…But surface failure is not known to lead to VHCF in high‐strength steels. For fatigue test with artificial surface defects, only if fatigue tests are performed in vacuum VHCF cracks initiate by FGA formation as shown by Spriestersbach et al In an air environment, no surface failure is observed for high‐strength steels in VHCF in these tests with surface defects. Thus, for high‐strength steels, the threshold for surface failure definitely would be questionable.…”

Section: Introductionmentioning

confidence: 89%

Threshold values for very high cycle fatigue failure of high‐strength steels

Spriestersbach

Grad

Kerscher

2017

Fatigue Fract Eng Mat Struct

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Cracks leading to failure in very high cycle fatigue (VHCF) of high‐strength steels mostly initiate at subsurface inclusions at stress intensity factors (SIF) below the classical threshold value Kth for long cracks, especially for negative stress ratios. Here, a characteristic fine granular area (FGA) can be observed at the fracture surface in the vicinity of these initiating inclusions. According to various researchers, the FGA formation might be responsible for the late initiation of a propagable long crack. This study aims to clarify the threshold values of SIF for crack initiation for VHCF failure with FGA formation at nonmetallic inclusions. For this purpose, ultrasonic fatigue tests (R = −1) with the high‐strength steel 100Cr6 (SAE 52100) were carried out until an ultimate number of cycles of 109. In addition, very high cycle stress increase tests were performed. A serial grinding investigation of fatigued specimens acted as a technique to evaluate the distribution of unharmful inclusion in the tested volume. By the combination of these tests, a threshold value of the SIF for the VHCF by FGA formation at inclusions can be derived. This threshold value depends on the size of the crack initiating inclusion.

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Very high cycle fatigue of high-strength steels: Crack initiation by FGA formation investigated at artificial defects

Cited by 38 publications

References 20 publications

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

Influence of mean stress and notches on the very high cycle fatigue behaviour and crack initiation of a low‐pressure steam turbine steel

Threshold values for very high cycle fatigue failure of high‐strength steels

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