Very high cycle fatigue of bearing steels with artificial defects in vacuum

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

doi:10.1080/02670836.2015.1119931

Cited by 23 publications

(11 citation statements)

References 29 publications

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“…The characteristics of FGA in VHCF of high-strength steels have been reported in detail by several researchers. 34,35,38,46,47 However, for the VHCF of titanium alloys, the present paper is likely the first time to reveal the nature of nanograins in and only in the RA of fatigue crack initiation for the case of R = À1. The notch effect and the size effect on VHCF behavior for titanium alloys are also very important topics.…”

Section: It Is Shown Inmentioning

confidence: 85%

Nanograin layer formation at crack initiation region for very‐high‐cycle fatigue of a Ti–6Al–4V alloy

Liu

Sun

et al. 2016

Fatigue Fract Eng Mat Struct

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A B S T R A C T The microstructural features and the fatigue propensities of interior crack initiation region for very-high-cycle fatigue (VHCF) of a Ti-6Al-4V alloy were investigated in this paper. Fatigue tests under different stress ratios of R = À1, À0.5, À0.1, 0.1 and 0.5 were conducted by ultrasonic axial cycling. The observations by SEM showed that the crack initiation of VHCF presents a fish-eye (FiE) morphology containing a rough area (RA), and the FiE and RA are regarded as the characteristic regions for crack initiation of VHCF. Further examinations by TEM revealed that a layer of nanograins exists in the RA for the case of R = À1, while nanograins do not appear in the FiE outside RA for the case of R = À1, and in the RA for the case of R = 0.5, which is explained by the Numerous Cyclic Pressing model. In addition, the estimations of the fatigue propensities for interior crack initiation stage of VHCF indicated that the fatigue life consumed by RA takes a dominant part of the total fatigue life and the related crack propagation rate is rather slow.Keywords crack initiation; fatigue life; nanograins; Ti-6Al-4V alloy; very-high-cycle fatigue. N O M E N C L A T U R E2a FiE = equivalent diameter of FiE 2a RA = equivalent diameter of RA ffiffiffiffiffiffiffiffi ffi area p = equivalent size of FiE or RA A, m = material parameters BFI = bright field image BSE = back scattered electron (imaging) EG = equiaxed α grain FIB = focused ion beam FiE = fish-eye FGA = fine granular area HAADF = high angle annular dark field (imaging) ΔK FiE = range of SIF in FiE region ΔK RA = range of SIF in RA ΔK th = threshold of SIF LM = lamellar structure NCP = numerous cyclic pressing NG = nanograin N f = total fatigue life N i = fatigue life of crack initiation RA = rough area SAD = selected (electron) area diffraction SIF = stress intensity factor VHCF = very-high-cycle fatigue

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Section: It Is Shown Inmentioning

confidence: 85%

Nanograin layer formation at crack initiation region for very‐high‐cycle fatigue of a Ti–6Al–4V alloy

Liu

Sun

et al. 2016

Fatigue Fract Eng Mat Struct

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“…grain refinement) is caused by the interaction between the dislocations in the vicinity of crack origin or initiated crack tip due to local high stress [33]. The micro crack forms within the refined grains [29,34] due to the decrease of threshold value for crack initiation in regions of fine grains [35], or along the fine graincoarse grain interface. The first case would lead to the observation of fine grains in the mated fracture surfaces; and the second case would give rise to observation of fine grains only in one side of the fracture surface.…”

Section: Discussionmentioning

confidence: 99%

The formation of discontinuous gradient regimes during crack initiation in high strength steels under very high cycle fatigue

Sun

Song

Zhou

et al. 2019

International Journal of Fatigue

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While fatigue is ubiquitous and is responsible for a large proportion of failure in engineering structures, we understand little regarding the mechanism of crack initiation and early-stage crack growth especially for very high cycle fatigue (VHCF) behavior. We identified in this report the microstructural evolution during interior crack initiation and early growth in a martensitic stainless steel in VHCF regime by constant and variable amplitude loading method. We observed in the post-mortem samples after VHCF a discontinuous gradient layer composed of ultrafine grains and coarse grains in the fractured surfaces using both electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The gradient ultrafine grains are resulted from excessive cyclic plastic deformation in the vicinity of the crack origin or crack tip, which promotes the formation of crack initiation. The equivalent crack growth rate in FGA (fine granular area) is also estimated based on the "tree ring" patterns under variable amplitude loading, which is in the magnitude of 10 −12-10 −11 m/cyc.

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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 bearing steels with artificial defects in vacuum

Cited by 23 publications

References 29 publications

Nanograin layer formation at crack initiation region for very‐high‐cycle fatigue of a Ti–6Al–4V alloy

Nanograin layer formation at crack initiation region for very‐high‐cycle fatigue of a Ti–6Al–4V alloy

The formation of discontinuous gradient regimes during crack initiation in high strength steels under very high cycle fatigue

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

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