Characterization of fatigue crack-initiation facets in relation to lifetime variability in Ti–6Al–4V

Golden, Patrick J.; John, Reji; Jha, S. K.; Szczepanski, C J; Porter, William

doi:10.1016/j.ijfatigue.2011.11.017

Cited by 113 publications

(58 citation statements)

References 20 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%

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%

Reducing uncertainty in fatigue life limits of turbine engine alloys

Larsen

Jha

Szczepanski

et al. 2013

International Journal of Fatigue

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“…Two types of fatigue fracture surface for faceted crack initiation, i.e. surface-with-facets (crack initiation from the surface of specimen with subsurface facets) and interior-with-facets (crack initiation from the interior of specimen with facets) were reported in HCF and VHCF regimes of a Ti-6Al-4V alloys, and no pre-existed defects were observed in the crack initiation region [9]. The faceted morphology was in relation with the cleavage of primary a grains [10], and the groups of primary a grains that formed facets were regarded as the clusters of primary a grains [11].…”

Section: Introductionmentioning

confidence: 99%

Faceted crack initiation characteristics for high-cycle and very-high-cycle fatigue of a titanium alloy under different stress ratios

Liu

Sun

Hong

2016

International Journal of Fatigue

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a b s t r a c tUltrasonic fatigue tests were conducted at the stress ratios of À1, À0.5, À0.1, 0.1 and 0.5 for a Ti-6Al-4V alloy in high-cycle and very-high-cycle fatigue regimes. Experimental results showed that faceted crack initiation was the main failure mode for specimens at the stress ratios of À0.1, 0.1 and 0.5, and multi-site faceted crack initiation was observed at the stress ratios of 0.1 and 0.5. The measurements indicated that the number of facets increased with the increase of stress ratio. Based on the observations, the mechanism of faceted crack initiation was proposed, i.e., (i) cleavage of isolated primary a grains in cluster; (ii) gradual growth of originated cracks (facets), and the coalescence of adjacent facets; and (iii) coalesced facets forming a main crack in the cluster. Moreover, a model based on Poisson defect distribution is proposed to describe the effects of stress ratio on faceted crack initiation, which is in agreement with the experimental results.

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“…The initiation facets were found to lie around 10 • from the basal plane. Surface facets were tilted 30 • , whilst subsurface facets were 30 • − 60 • towards the loading direction [6]. The point of fracture origin is susceptible to the loading conditions and can also occur subsurface [7].…”

Section: Introductionmentioning

confidence: 99%

Influence of complex LCF and dwell load regimes on fatigue of Ti–6Al–4V

et al. 2016

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Real components are usually subjected to variable amplitude fatigue, and yet the deformation micromechanisms that occur due to such load changes have barely been the subject of study. Here, unidirectionally rolled equiaxed Ti6Al-4V plate was subjected to mixed dwell and variable amplitude low cycle fatigue (LCF), with the finding that overloads near the yield stress were found to retard subsequent fatigue crack growth, whilst elastic underloads were found to accelerate subsequent growth. Dwell intervals were found to be especially damaging, to a far greater extent than either dwell or LCF alone. Dwell facets were found to initiate subsurface and to be smoother than LCF facets, but were otherwise similar in orientation (∼ 30 • to the loading axis) and crystallographic plane, 2-13 • from (0002). However, no alteration of the slip bands underlying striations was observed at the point of load changes using TEM. In failure investigation, striation counting is an important tool; the loading changes used were not found to affect the number of striations formed. Dislocation networks were found between similarly oriented grains in the as-received material, which disintegrated under dwell loading and at high stresses.

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Characterization of fatigue crack-initiation facets in relation to lifetime variability in Ti–6Al–4V

Cited by 113 publications

References 20 publications

Reducing uncertainty in fatigue life limits of turbine engine alloys

Reducing uncertainty in fatigue life limits of turbine engine alloys

Faceted crack initiation characteristics for high-cycle and very-high-cycle fatigue of a titanium alloy under different stress ratios

Influence of complex LCF and dwell load regimes on fatigue of Ti–6Al–4V

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