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Research Papers: Gas Turbines: Structures and Dynamics

Life Prediction for Turbopropulsion Systems Under Dwell Fatigue Conditions

[+] Author and Article Information
Kwai S. Chan

ASME Fellow

Jonathan P. Moody

Southwest Research Institute®,
San Antonio, TX 78238

Simeon H. K. Fitch

Elder Research Inc.,
Charlottesville, VA 22903

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 15, 2012; final manuscript received June 27, 2012; published online October 11, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 134(12), 122501 (Oct 11, 2012) (8 pages) doi:10.1115/1.4007321 History: Received June 15, 2012; Revised June 27, 2012

The objective of this investigation was to develop an innovative methodology for life and reliability prediction of hot-section components in advanced turbopropulsion systems. A set of three generic time-dependent crack growth models was implemented and integrated into the Darwin® probabilistic life-prediction code. Using the enhanced risk analysis tool and material constants calibrated to IN 718 data, the effect of time-dependent crack growth on the risk of fracture in a turboengine component was demonstrated for a generic rotor design and a realistic mission profile. The results of this investigation confirmed that time-dependent crack growth and cycle-dependent crack growth in IN 718 can be treated by a simple summation of the crack increments over a mission. For the temperatures considered, time-dependent crack growth in IN 718 can be considered as a K-controlled environmentally-induced degradation process. Software implementation of the generic time-dependent crack growth models in Darwin provides a pathway for potential evaluation of the effects of multiple damage modes on the risk of component fracture at high service temperatures.

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Figures

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Fig. 1

The proposed methodology enables designers and analysts to perform life and reliability on hot-section components subject to aggressive mission profiles with high peak temperature and long dwell times that can lead to time-dependent damage modes such as creep, stress rupture, and stress corrosion. The Darwin enhancements developed under this study will enable the analyst to compute reliability contours such as oxygen-assisted cracking along a grain boundary as shown schematically in this figure.

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Fig. 2

Schematics of time-dependent crack growth curves of Ni-based superalloys at elevated temperatures: (a) K-controlled crack growth, and (b) diffusion-controlled crack growth

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Fig. 3

Experimental data for crack growth at 1100 °F and 1200 °F with power law fits

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Fig. 4

A comparison of the da/dt data of IN 718 for SF and CT specimens without and with 2 min dwell (2 MDW) from the PDRI dataset [2]

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Fig. 5

(a) Log-log plot of B versus reciprocal absolute temperature for IN 718, and (b) log-linear plot of da/dt versus reciprocal absolute temperature for IN 718 from the PDRI dataset [2], Sadananda and Shahinian (S&S) [13], and Browning [12]

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Fig. 6

Fatigue crack growth rate of IN 718 at K = 25 ksi(in)1/2 as a function of frequency at various temperatures. Time-dependent fatigue crack growth is observed only in air at temperatures at or above 1000 °F. Cycle-dependent fatigue crack growth is observed in IN 718 at temperatures at or below 750 °F and at 1200 °F in vacuum. IN 718 data are from the PDRI dataset [2], UDRI [6], and Chang et al. [11].

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Fig. 7

Comparisons of computed and measured fatigue crack growth response of IN 718 with and without a 2 min dwell (2 MDW): (a) 1100 °F, and (b) 1200 °F. Experimental data are from the PDRI Program [2].

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Fig. 8

Comparison of computed and measured fatigue crack growth response of IN 718 at K = 25 ksi(in.)1/2 as a function of frequency for 1100 °F and 1200 °F. Experimental data are from the PDRI Program [2].

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Fig. 9

Comparison of computed and measured fatigue crack growth response of IN 718 at K = 25 ksi(in)1/2 as a function of frequency at various temperatures ranging from 75 °F to 1200 °F. Experimental data are from the PDRI Program [2], UDRI [6], and Chang et al. [11].

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Fig. 10

Finite-element model of a gas turbine rotor design selected for the time-dependent crack growth demonstration problem using Darwin

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Fig. 11

Surface anomaly distribution utilized in the Darwin demonstration problem

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Fig. 12

Darwin results of maximum stress intensity, Kmax, as a function of flight cycle for the demonstration problem

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Fig. 13

Darwin results of cracked area as a function of flight cycle for the rotor design used in the demonstration problem

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Fig. 14

Computed conditional probability of fracture as a function of flight cycle for the rotor design used in the demonstration problem

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