A model to predict S–N curves for surface and subsurface crack initiations in different environmental media

Qian, Guian; Zhou, Chan; Hong, Youshi

doi:10.1016/j.ijfatigue.2013.11.013

Cited by 32 publications

(29 citation statements)

References 46 publications

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“…However, it is widely accepted that corrosion fatigue crack initiation points are due to surface defects (such as corrosion pits and voids) of aluminium alloys caused by NaCl aqueous solutions by previous literature. 10,[13][14][15]27,28 In addition, effects of second cracks of high-strength aluminium alloy, 7475-T7351 and 7075-T651, as shown in Fig. 2a and b, and voids of high-ductility aluminium alloys, LY12-CZ and 2024-T4, as shown in Fig.…”

Section: R E S U L T S a N D Discussion Smentioning

confidence: 94%

“…In recent years, many studies have focused on the fatigue behaviour of Al alloys in the corrosive environment. 14 Li et al 15 estimated the effect of pre-corrosion states on the fatigue microcrack initiation and early stage propagation behaviour of 6151-T6 aluminium alloy based on scanning electron microscopy (SEM) in situ observation. Hui et al 16 and Qian et al…”

Section: Introductionmentioning

confidence: 99%

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Synergistic effect of environmental media and stress on the fatigue fracture behaviour of aluminium alloys

Yang

Wang

et al. 2016

Fatigue Fract Eng Mat Struct

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A B S T R A C T The present study aims at explaining the synergistic effect of environmental media and stress/strain on fatigue lives of aluminium alloys. Rotating bending fatigue tests were carried out using four different aluminium alloys LY12-CZ, 2024-T4, 7475-T7351 and 7075-T651, at air state, 3.5% and 5.0% NaCl aqueous solutions. These results indicated that synergistic actions of the environmental media and cyclic loading accelerated the fatigue crack propagation of aluminium alloys. Furthermore, various influence factors (such as solution concentration, cyclic numbers, high (low) strength aluminium alloys etc.) of the fatigue life at synergistic actions of the environmental media and stress were quantificationally discussed in this paper.Keywords aluminium alloy; corrosion environment; fatigue life; fracture behaviour; synergistic effect. N O M E N C L A T U R Eα = the stress concentration factor (1.08) B, C = the distance between adjacent striations, respectively d, L = the geometry size, respectively g = the acceleration of gravity (9.8 m/s 2 ) N f = number of cycles to failure σ = stress amplitude (MPa) R = stress ratio I N T R O D U C T I O NThere have been growing interests in light metals, such as aluminium, magnesium and titanium-aluminium alloys, which have been widely applied to aeronautic and automotive industries because of their high strength-toweight ratios, 1-3 but improvements are needed in their fatigue properties, 4-8 very high-cycle fatigue behaviour of aluminium alloys 9-11 and some factors of high humidity on fatigue properties of aluminium alloys. 12As one of the important materials in aeronautic and automotive structures, the aluminium alloy is usually directly exposed to the corrosive environment with stress/strain, 13 in which the corrosive fatigue cracking mechanism is rather a complex process and needs to be deeply understood. More data, especially fatigue properties in such an environment, are crucial for safety. In recent years, many studies have focused on the fatigue behaviour of Al alloys in the corrosive environment.14 Li et al. 15estimated the effect of pre-corrosion states on the fatigue microcrack initiation and early stage propagation behaviour of 6151-T6 aluminium alloy based on scanning electron microscopy (SEM) in situ observation. Hui et al. 16 and Qian et al.14 conducted fatigue life tests in the laboratory air and salt water environment by using several pre-corrosion 7XXX aluminium alloys and a structural steel 40Cr and reported that the salt water environment significantly reduced the fatigue performance, especially under low stress amplitude and the fatigue life is about 2.2% of that at air state. These results indicated that the effect of different pre-corrosion states on the fatigue damage of aluminium alloys is mainly producing more stress concentration sites (or pits) and inducing more fatigue cracks. Zhang et al. 17proposed a novel model to predict the residual fatigue life of 2A12 aluminium alloy subjected to alternating corrosion and fatigue based on the ...

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Section: R E S U L T S a N D Discussion Smentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Synergistic effect of environmental media and stress on the fatigue fracture behaviour of aluminium alloys

Yang

Wang

et al. 2016

Fatigue Fract Eng Mat Struct

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“…It has been known that a fatigue crack always initiates from the interior of specimen for VHCF, 9,10 which is different from the surface crack initiation mechanism for low-cycle fatigue and high-cycle fatigue. 11,12 In addition, the unique influences of stress ratio, [13][14][15] strength level, 16 loading frequency, 16,17 specimen size 18,19 and environmental condition 20,21 on the behavior of VHCF have been reported. However, the theories of physics and mechanics for the explanation of VHCF experiments still need further development.…”

Section: Introductionmentioning

confidence: 99%

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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“…For high-strength steels, cracks are prone to initiate at specimen subsurface or interior [9][10][11][12][13] in VHCF regime, and a distinct crack initiation feature of ''fish-eye" morphology embracing a region of ''fine-granular-area (FGA)" usually presents at fracture surface. Another typical feature of VHCF behavior for highstrength steels is that the S-N curve is a stepwise or duplex shape [14][15][16][17][18][19][20][21] with regard to surface-induced and interior-induced crack initiation, respectively. Bathias and Paris [22] investigated several high-strength steels via ultrasonic fatigue test technique and revealed that subsurface crack initiated from either nonmetallic inclusions or other microstructural inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

“…Their result demonstrated that the formation of FGA is responsible for a majority part of total fatigue life and the fraction of fatigue life contributed by FGA is beyond 95% in VHCF regime. Further, a D ⁄ parameter has been proposed to discuss the competition of crack initiation from the surface and from the interior of specimen [20,21], which gave an explanation for the preference of fatigue crack initiation either from the surface or from the interior of specimen.…”

Section: Introductionmentioning

confidence: 99%

Very-high-cycle fatigue behavior of a structural steel with and without induced surface defects

Jiang

Sun

Liu

et al. 2016

International Journal of Fatigue

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a b s t r a c tFatigue tests via rotary bending were performed on the specimens with and without induced surface defects for a structural steel of medium carbon content to investigate the effect of surface defects on fatigue behavior in high-cycle fatigue and very-high-cycle fatigue (VHCF) regimes. The S-N data showed that induced surface defects substantially degraded the related fatigue strength. For the specimens without surface defects failed in VHCF regime, crack initiated from the interior of specimens with inclusions or matrix inhomogeneities as crack origin and the initiation regions were of different extents of rough surface. The observations on the profile samples cut from crack initiation regions revealed that the region was a layer of nanograins for the case of inclusion as crack origin, and was without grain refinement for the case of grain boundary as crack origin. For the specimens with induced surface defects, crack initiated from surface defects and the initiation region was without grain refinement. The characteristics of crack initiation were carefully examined and the effect of surface defects on fatigue strength degradation was analyzed by available models.

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A model to predict S–N curves for surface and subsurface crack initiations in different environmental media

Cited by 32 publications

References 46 publications

Synergistic effect of environmental media and stress on the fatigue fracture behaviour of aluminium alloys

Synergistic effect of environmental media and stress on the fatigue fracture behaviour of aluminium alloys

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

Very-high-cycle fatigue behavior of a structural steel with and without induced surface defects

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