Influence of mean stresses on fatigue life and damage of a turbine blade steel in the VHCF-regime

Kovacs, Stephan; Beck, T.; Singheiser, L.

doi:10.1016/j.ijfatigue.2012.12.012

Cited by 98 publications

(100 citation statements)

References 32 publications

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“…in Ti alloys [13] and in steels [14]. Kovacs [14] also reported the failure of martensitic steels (X10CrNiMoV12-2-2) in fatigue at high mean stresses with a typical ratchetting failure at a very high stress ratio (R = 0.7) and thus consistent with interpretation and observation in this study. …”

Section: Fatigue Livessupporting

confidence: 91%

Fatigue life and crack growth behavior of post welded Aluminum 5183 alloy

Gaur

Enoki

Okada³

et al. 2018

MATEC Web Conf.

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Abstract. In this study we investigated the fatigue life and crack growth behavior of Al-5183 alloy. Microscopic analysis revealed nearly equi-axed grains and no texture in longitudinal or cross-sectional plane of the welded plates. Gas porosities with an average size of 45 μm, comparable to grain size (55 μm), were present and often initiate fatigue failures. Load-controlled cyclic tests at different stress-ratios (R = -1, -0.5, 0.1, 0.5. 0.7 and 0.8) revealed decrease in fatigue lives with increase in R-ratio. At R > 0.7, no fatigue failure could be observed, suggesting a probable mean-stress saturation effect on fatigue. Mean stress also tends to control the crack initiation sites: surface initiated failures at low mean stresses while sub-surface pores induced failures at higher mean stresses. Fatigue-crack growth tests on CT specimens at different R-ratios (0.1, 0.5 and 0.8) revealed reduction in crack growth rates (and in threshold values) with increasing R-ratio. The ∆K applied for pores responsible for fatigue failures were often lower than or near to the threshold values and also, the size of such pores was of order of magnitude of grain size, thus crack initiated from pores are short cracks and further tests are progress.

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Section: Fatigue Livessupporting

confidence: 91%

Fatigue life and crack growth behavior of post welded Aluminum 5183 alloy

Gaur

Enoki

Okada³

et al. 2018

MATEC Web Conf.

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“…However, failures above 10 8 cycles were found for loading at R = 0, but not at R = -1 [23]. These results are similar to those found for martensitic 12 % Cr turbine steel (X10CrNiMoV12-2-2) that was tested in a wide range of load ratios between R = -1 and R = 0.7 [24]. Change of crack initiation from the surface in the HCF regime to subsurface in the VHCF regime was found for all load ratios.…”

Section: Introductionsupporting

confidence: 81%

“…No failures were detected above 10 8 cycles at load ratio R = -1. In contrast, failures above 10 8 cycles were found in experiments at load ratio R = 0.1, and fractures above 10 9 cycles occurred at load ratio R = 0.5 and R = 0.7 [24]. The influence of load ratio on the VHCF strength of a 12 % Cr martensitic steam turbine steel (grade 403/410) was investigated at load ratios between R = -1 and R = 0.8 [25].…”

Section: Introductionmentioning

confidence: 96%

Mean stress sensitivity of spring steel in the very high cycle fatigue regime

Schuller¹,

Karr²,

Irrasch³

et al. 2015

J Mater Sci

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The influence of load ratio on the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of shot-peened VDSiCr spring steel is investigated. S-N curves are measured with ultrasonic fatigue testing equipment at load ratio R = -1, R = 0.1 and R = 0.5 up to 10 10 cycles. Failures either occur below 5 9 10 6 or above 5 9 10 8 cycles. In the HCF regime cracks start exclusively at the surface. In the VHCF regime crack initiation occurs solely in the interior, at grain boundaries, inclusions or (rarely) in the matrix. The S-N curves continue to decrease beyond 10 9 cycles, most pronounced for R = -1 where the mean cyclic strength at 10 10 cycles is 5 % lower than at 10 9 cycles. VHCF strength presented in a Haigh diagram can be very well approximated with a straight line. The mean stress sensitivity factor is M = 0.47 for load ratios between R = -1 and R = 0.5.

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“…Another interesting case [26] is that, for a high-carbon bearing steel with axial cycling (50 Hz) under the stress ratios of R = 0 and R = 0.5, fatigue cracks initiated from the interior of specimen with FiE pattern and FGA morphology at the failure cycles of 6.22 Â 10 7 at R = 0, whereas the initiation region was with FiE but without FGA morphology at the failure cycles of 2.57 Â 10 5 at R = 0. A recently reported case [27] of VHCF for a martensitic 12% Cr steel (0.117% C), for which the specimens were tested by axial cycling (20 kHz) in laboratory air at the stress ratios from À1 to 0.7, showed that FGA was observed in the specimens at R = À1 but never found in the specimens fatigued at R = 0.1, 0.5 and 0.7. It is obvious that the presence or the absence of FGA in the crack initiation process of VHCF in above cases cannot be explained or reconciled by the existed proposed mechanisms.…”

Section: Introductionmentioning

confidence: 98%

The formation mechanism of characteristic region at crack initiation for very-high-cycle fatigue of high-strength steels

Hong

Liu

Lei

et al. 2016

International Journal of Fatigue

232

165

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a b s t r a c tFor high-strength steels, the crack initiation of very-high-cycle fatigue (VHCF) is commonly at the interior of material with fish-eye (FiE) morphology containing a fine-granular-area (FGA) surrounding an inclusion as crack origin, and FGA is regarded as the characteristic region of crack initiation. Here, we carefully examined the micro-morphology of FGA and FiE for two high-strength steels. The results revealed that the microscopic nature of FGA is a thin layer of nanograins. Then we proposed the formation mechanism of FGA: Numerous Cyclic Pressing (NCP) between originated crack surfaces, which causes grain refinement at originated crack wake and therefore the formation of FGA. The results of second set experiment showed that the cases with negative stress ratios exhibit the prevalence of nanograin layer in FGA region and the nanograin layer vanishes for the cases with positive stress ratios, which is a verification of the proposed NCP model.

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Influence of mean stresses on fatigue life and damage of a turbine blade steel in the VHCF-regime

Cited by 98 publications

References 32 publications

Fatigue life and crack growth behavior of post welded Aluminum 5183 alloy

Fatigue life and crack growth behavior of post welded Aluminum 5183 alloy

Mean stress sensitivity of spring steel in the very high cycle fatigue regime

The formation mechanism of characteristic region at crack initiation for very-high-cycle fatigue of high-strength steels

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