A new paradigm of fatigue variability behavior and implications for life prediction

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

doi:10.1016/j.msea.2006.10.171

Cited by 67 publications

(86 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4), while some of the specimens failed from internal initiation sites under maximum stresses of 860 MPa or lower. Further details on the microstructure, experimental methods, results, and analysis are provided in [37,[39][40][41]54], which served as the backbone of the results to be presented below. residual-stress-free electropolished surfaces.…”

Section: Materials and Experimental Methodsmentioning

confidence: 99%

“…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%

“…In exploring this behavior in turbine engine alloys, we have developed a physically-based approach for describing fatigue variability, and this approach has been integrated into a Monte Carlo probabilistic life prediction model for materials [35,40,52]. The primary tenets of our fatigue variability description are summarized by [40]: (i) under nominal microstructural and loading conditions, a hierarchy of local deformation heterogeneities develop in a fatigue sample, corresponding to grain-scale cyclic micro-plasticity in certain microstructural arrangements or features; (ii) as a result of this hierarchy, a probability exists of an extreme microstructural arrangement that may initiate a crack-growth dominated failure, producing a life-limiting failure distribution for the material; and (iii) there are often different degrees of influence of a given variable on minimum vs. the mean lifetimes.…”

Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

“…The primary tenets of our fatigue variability description are summarized by [40]: (i) under nominal microstructural and loading conditions, a hierarchy of local deformation heterogeneities develop in a fatigue sample, corresponding to grain-scale cyclic micro-plasticity in certain microstructural arrangements or features; (ii) as a result of this hierarchy, a probability exists of an extreme microstructural arrangement that may initiate a crack-growth dominated failure, producing a life-limiting failure distribution for the material; and (iii) there are often different degrees of influence of a given variable on minimum vs. the mean lifetimes. For example, the effect of stress level on mean vs. life-limiting fatigue typically produces quite different responses, and such differing response of minimum and mean fatigue behavior has been observed for other important variables, including microstructure, surface treatment, temperature, and dwell time.…”

Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

See 3 more Smart Citations

Reducing uncertainty in fatigue life limits of turbine engine alloys

Larsen

Jha

Szczepanski

et al. 2013

International Journal of Fatigue

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Materials and Experimental Methodsmentioning

confidence: 99%

Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

Section: Life Limits and Competing-mode Of Fatiguementioning

confidence: 99%

See 2 more Smart Citations

Reducing uncertainty in fatigue life limits of turbine engine alloys

Larsen

Jha

Szczepanski

et al. 2013

International Journal of Fatigue

Self Cite

View full text Add to dashboard Cite

show abstract

“…In materials containing large amounts of discontinuities like surface and internal inclusions, fatigue cracks initiate at these discontinuities most likely due to the lower toughness of the discontinuities compared with the matrix [45][46][47][48][49][50][51]. If a fatigue crack forms at an inclusion and begins to propagate depends on the type of inclusion, size of the inclusion, distribution of inclusion and residual stresses present.…”

Section: Fatigue 15mentioning

confidence: 99%

Cracks in superalloys

Saarimäki¹

View full text Add to dashboard Cite

Linköping 2018Cover image: An orientation imaging map illustrating the general crack propagation behaviour of a 2160 s dwell-time tested Inconel 718 bar run at 550 ○ C, with a 15 % superimposed overload at the beginning of the dwell-time.During the course of research underlying this thesis, Jonas Saarimäki was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Jonas Saarimäki AbstractGas turbines are widely used in industry for power generation and as a power source at hard to reach locations where other possibilities for electrical power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects.The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD).The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when iii iv an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ-phase boundaries with subsequent oxidation of the δ phase.This thesis comprises two parts. Part I gives an introducti...

show abstract

The Variability of Fatigue in Notched Bars of IN100

Rosenberger

Buchanan

Ward³

et al. 2012

Superalloys 2012

View full text Add to dashboard Cite

IN100 is one of the workhorse nickel-base superalloys of the current fleet of turbine engines owned and operated by the US Air Force. Many of the life-limited locations on fracture critical IN100 components are associated with locations of stress concentrations, e.g. bolt holes, fillets, balance flange scallops, etc. The prior work by Jha, Caton, and others [1-3] examining the fatigue variability of nickel-base superalloys found a link between the minimum fatigue life and fracture mechanics. That is, the minimum fatigue life was predicted assuming immediate crack initiation and growth of a small crack. This prior work only examined the fatigue behavior of smooth fatigue bars. The current effort determined that the link between minimum fatigue life and fracture mechanics is applicable even when only a small volume of the material at the root of a notch is subject to the high stress conditions.

show abstract

A new paradigm of fatigue variability behavior and implications for life prediction

Cited by 67 publications

References 25 publications

Reducing uncertainty in fatigue life limits of turbine engine alloys

Reducing uncertainty in fatigue life limits of turbine engine alloys

Cracks in superalloys

The Variability of Fatigue in Notched Bars of IN100

Contact Info

Product

Resources

About