The role of competing mechanisms in the fatigue-life variability of a titanium and gamma-TiAl alloy

Jha, S. K.; Larsen, J. M.; Rosenberger, A. H.

doi:10.1007/s11837-005-0116-z

Cited by 7 publications

(6 citation statements)

References 26 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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“…The Weibull distribution of fatigue lifetimes of the SP samples at stress amplitudes of 260 MPa also revealed the bimodal distribution found in the S-N-diagram (Figure 6). The two failure mechanisms are considered separately, analogous to Jha et al [7]. Crack initiation from the surface led to a lower characteristic lifetime of~4.34 × 10 5 cycles.…”

Section: Lifetime Results and Crack Initiation Behaviormentioning

confidence: 96%

“…For volume cracks, the environmental influence on crack propagation is suppressed [16,17]; thus, an increase in cyclic lifetime can be expected. A strong dependence of the fatigue lifetime on the crack initiation site was reported in [7]. The effect of shot peening on the room temperature fatigue behavior of different γ-TiAl alloys was the subject in several publications, e.g., [15,18], and it is found that shot peening can improve the fatigue resistance for this class of material.…”

Section: Introductionmentioning

confidence: 98%

“…In service, turbine blades endure creep and fatigue loading, which typically determine their lifetime. While the isothermal and thermomechanical fatigue properties of TiAl alloys have been studied several times, see, e.g., [6][7][8][9][10][11][12], little attention has been paid to the possibilities of mechanical surface treatments such as shot peening to possibly achieve higher cyclic lifetimes.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

Breuner

Guth

Gall

et al. 2021

Metals

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One possibility to improve the fatigue life and strength of metallic materials is shot peening. However, at elevated temperatures, the induced residual stresses may relax. To investigate the influence of shot peening on high-temperature fatigue behavior, isothermal fatigue tests were conducted on shot-peened and untreated samples of gamma TiAl 48-2-2 at 750 °C in air. The shot-peened material was characterized using EBSD, microhardness, and residual stress analyses. Shot peening leads to a significant increase in surface hardness and high compressive residual stresses near the surface. Both effects may have a positive influence on lifetime. However, it also leads to surface notches and tensile residual stresses in the bulk material with a negative impact on cyclic lifetime. During fully reversed uniaxial tension-compression fatigue tests (R = −1) at a stress amplitude of 260 MPa, the positive effects dominate, and the fatigue lifetime increases. At a lower stress amplitude of 230 MPa, the negative effect of internal tensile residual stresses dominates, and the lifetime decreases. Shot peening leads to a transition from surface to volume crack initiation if the surface is not damaged by the shots.

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“…However, some have also pointed out that dwell-fatigue properties can vary within a single forged part (Davies, 1997;Ress, 1995;Uta, 2009). Titanium alloys are known to have texture heterogeneities, i.e., regions much larger than the grain dimensions where the local orientation distribution of the grains differs from one region to the next (Germain et al, 2005;Jha et al, 2005;Le Biavant-Guerrier, 2000;Moreau et al, 2013;Toubal et al, 2009aToubal et al, , 2009bToubal et al, , 2010. These relatively large regions, sometimes of millimetric dimensions, present specific crystallographic orientations and play a significant role in the early dwellfatigue damage of titanium parts (Le Biavant-Guerrier, 2000;Uta et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Bimodal dwell-fatigue Weibull distribution of forged titanium IMI 834

Toubal

Bocher

Moreau

2014

International Journal of Damage Mechanics

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This study addresses cumulative damage and its evolution during the cold dwell fatigue of a neartitanium alloy. An experimental study was undertaken to examine the evolution of life, strain, strength and damage of 13 titanium IMI 834 samples cut from a single disk forging. The samples were tested in the same dwell-fatigue loading conditions. In the dwell phase, the load is maintained at 80% of ultimate tensile strength (824 MPa, 90% of yield strength) for 30 s. The secant Young's modulus and inelastic strain at minimum load were measured in order to document the evolution of the irreversible damage against the number of cycles for all specimens. Experimental observations show significant differences in dwell-fatigue life and damage behavior. This mechanical analysis and an analysis of the cumulative Weibull reliability distribution suggest a bimodal dwell-fatigue failure process. Some features of the mechanical behavior can be used to sort the samples according to each of the two failure modes and improve the reliability of the fatigue test campaign.

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The role of competing mechanisms in the fatigue-life variability of a titanium and gamma-TiAl alloy

Cited by 7 publications

References 26 publications

Reducing uncertainty in fatigue life limits of turbine engine alloys

Reducing uncertainty in fatigue life limits of turbine engine alloys

Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

Bimodal dwell-fatigue Weibull distribution of forged titanium IMI 834

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