Mean vs. Life-Limiting Fatigue Behavior of a Nickel Based Superalloy

Jha, S. K.; Caton, M. J.; Larsen, J. M.

doi:10.7449/2008/superalloys_2008_565_572

Cited by 29 publications

(39 citation statements)

References 10 publications

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“…2. This separation in fatigue lifetimes, known as bimodal or competing-modes fatigue, has been observed in a wide range of alloys, including the superalloys: Rene'95 [21,22], Rene'88DT [23], IN100 [8,[24][25][26][27][28][29], Waspaloy [30], the single crystal alloy PWA 1484 [31], the titanium alloys Ti-10-2-3 [23,[32][33][34], Ti-6Al-2Sn-4Zr-6Mo [35][36][37][38][39][40][41][42], Ti-6Al-4V [43][44][45][46][47], gamma titanium aluminides [48,49], the aluminum alloy 7075-T651 [50], and others. Although such a separation of fatigue response has been known for some time [51], the significance of this behavior has not yet been generally captured in the strategies for fatigue design of turbine engine materials.…”

Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

“…As noted earlier, we previously established a general computational framework for physics-based understanding of fatigue variability [24,40]. In this approach, the lifetime distribution was modeled as a superposition of the probability densities of the crack-growth-dominated lifetime (Type I) and the crack-initiation-dominated, mean lifetime (Type II).…”

Section: Modeling Bimodal Fatiguementioning

confidence: 99%

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Reducing uncertainty in fatigue life limits of turbine engine alloys

Larsen

Jha

Szczepanski

et al. 2013

International Journal of Fatigue

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a b s t r a c tIn probabilistic design of materials for fracture-critical components in modern military turbine engines, a typical maximum design target risk (DTR) is 5 Â 10 À8 component failures/engine flight hour. This metric underscores the essential role of safety in a design process that simultaneously strives to achieve performance, efficiency, reliability, and affordability throughout the life cycle of the engine. Traditionally, the design and life management approaches for engine materials have typically relied on extensive testing programs to produce large databases of fatigue data, from which statistically based life limits are derived by extrapolation from the mean fatigue behavior. However, we have found that the statistical behavior of fatigue lifetimes under a given test condition often exhibits a bimodal form, and that the trends in mean vs. minimum fatigue lifetime typically respond differently to loading or to microstructural variables. Under such circumstances, the underlying life-limiting mechanisms appear to exhibit a probabilistic microstructural hierarchy in fatigue resistance that is controlled by susceptibility of local microstructural neighborhoods to early damage and the growth of small cracks. These findings suggest that significant opportunities may exist for reductions in uncertainty in materials life-cycle prediction and management, if such hierarchies can be understood and controlled. This paper explores the potential implications of these findings, and a number of possible approaches are suggested for incorporating the insights of life-limiting fatigue into methods of integrated computational materials engineering (ICME) to support optimized life-cycle design of materials and components in turbine engines. Benefits of this approach appear to include substantial improvements in model accuracy, coupled with reduced requirements for materials testing, potentially leading to a significant reduction in the time and cost to develop, validate, transition, and implement new, more fatigue resistant alloys. Published by Elsevier Ltd.

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Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

Section: Modeling Bimodal Fatiguementioning

confidence: 99%

Reducing uncertainty in fatigue life limits of turbine engine alloys

Larsen

Jha

Szczepanski

et al. 2013

International Journal of Fatigue

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“…In Ti-6-2-4-6, this has been attributed to a superposition of the crack-growth-controlled (life-limiting) mechanism with the crack-initiationdominated (mean) behavior [27]. The effect of microstructural and extrinsic variables on the lifetime variability can then be modeled in terms of the distinct influence of these on the crack initiation and growth regimes, affecting the degree of separation between the two superimposing behaviors, as shown in [27][28][29]. In terms of the crack-initiation mechanism, in the RS-free condition (i.e., electropolished surface), failures occurred exclusively by surface-initiation, as indicated in Fig.…”

Section: Fatigue Variability Behavior In the Rs-free Conditionmentioning

confidence: 99%

“…However, this aspect has not been sufficiently addressed in past SP studies. In the RS-free condition, for instance, it has been demonstrated that the average microstructure or the distribution about the mean characteristics is not an accurate predictor of the lifetime variability [27,28]. In particular, the lower-tail of lifetime has been shown to be often controlled by an extreme microstructural configuration or arrangement, which otherwise has a small probability of occurrence, and may not be accounted for in conventional statistical characterization of microstructure [29].…”

Section: Introductionmentioning

confidence: 99%

Nominal Versus Local Shot-Peening Effects on Fatigue Lifetime in Ti-6Al-2Sn-4Zr-6Mo at Elevated Temperature (Preprint)

Jha¹,

John²,

Larsen³

2008

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information AFRL-RX-WP-TP-2008-4342 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTESPAO case number 88ABW-2008-0104, cleared 09 September 2008. This is a work of the U.S. Government and is not subject to copyright protection in the United States. Paper contains color. ABSTRACTA study of the elevated temperature fatigue lifetime variability in the shot-peened condition of the a+b titanium alloy, -Ti-6Al-2Sn-4Zr-6Mo, is presented. It is shown that failures separate into two distributions: (i) governed by the nominal residual stress profile, promoting subsurface crack initiation and longer lifetimes, and (ii) the life-limiting behavior that is controlled by localized material-shot-peening interaction. In the residual-stress-free condition, failures occurred predominantly by surface crack initiation at the microstructural scale, on the order of 10 um, by crystallographic facet formation in one of a few a particles and/or colonies. This mechanism was mitigated under the nominal shot-peening residual stress profile, producing failures initiating from the subsurface region by crystallographic faceting spread over a significantly larger area (equivalent diameter of about 100-200 um) thank in the absence of residual stress. SUBJECT TERMSFatigue variability, lifetime distribution, shot-peening, residual stress, Ti-6Al-2Sn-4Zr-6Mo AbstractA study of the elevated temperature (260°C) fatigue lifetime variability in the shot-peened condition of the α+β titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, is presented. It is shown that failures separate into two distributions: (i) governed by the nominal residual stress profile, promoting subsurface crack initiation and longer lifetimes, and (ii) the life-limiting behavior that is controlled by localized material -shot-peening interaction. In the residual-stress-free condition, failures occurred predominantly by surface crack initiation at the microstructural scale, on the order of 10 μm, by crystallographic facet formation in one or a few α particles and/or colonies.This mechanism was mitigated under the nominal shot-peening residual stress profile, producing failures initiating from the subsurface region by crystallographic faceting spread over a significantly larger area (equivalent diameter of about 100-200 μm) than in the absence of residual stress. Although the microstructure-scale surface crack-initiation was suppressed, the life-limiting failures under shot-peening continued to occur by ...

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“…Nowadays the maximum stress of the aero-engine turbine disk is approximately 1100 Mpa [5] (with the rotation speed 10000r/min). And considering the existing test data [6,7] , the stress levels were set at 1100MPa and 1200MPa for the low cycle fatigue and 900MPa and 1000MPa for the high cycle fatigue respectively.…”

Section: Experiments Proceduresmentioning

confidence: 99%

The study of the relationship between life limiting factor and stress level for FGH96

Yang

Shi

Miao³

et al. 2018

MATEC Web Conf.

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Abstract. FGH96 is a Chinese made powder metallurgy nickel based superalloy. This reserach aims to investigate the effect of stress on the microstructure of the worst fatigue life at 600℃. The specimens were first polished by abrasive paper and then electropolished to elimate the effect of surface residual stress. The fatigue tests were conducted at 600℃, and the loading ratio was 0.05 at the frequency of 5Hz. Tests were conducted at 900，1000，1100，1200MPa respectively. The fatigue life under the same condition were compared and the fractography of specimens were examined under SEM to further identify the lifelimiting factors of the material. The initiation mode transferred from facet initiated to inclusion initiated from lower stress level to higher stress level. Meanwhile, the initiation position transferred from internal to surface with the increase of stress level. This means at higher stress level, fatigue life is mainly limited by inclusion at surface while at lower stress level the limit is controlled by internal facet.

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Mean vs. Life-Limiting Fatigue Behavior of a Nickel Based Superalloy

Cited by 29 publications

References 10 publications

Reducing uncertainty in fatigue life limits of turbine engine alloys

Reducing uncertainty in fatigue life limits of turbine engine alloys

Nominal Versus Local Shot-Peening Effects on Fatigue Lifetime in Ti-6Al-2Sn-4Zr-6Mo at Elevated Temperature (Preprint)

The study of the relationship between life limiting factor and stress level for FGH96

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