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Research Papers: Gas Turbines: Structures and Dynamics

An Energy-Based Approach to Determine the Fatigue Strength and Ductility Parameters for Life Assessment of Turbine Materials

[+] Author and Article Information
M.-H. Shen

Professor
Fellow ASME
Department of Mechanical
and Aerospace Engineering,
The Ohio State University,
201 W. 19th Avenue,
Columbus, OH 43210
e-mail: shen.1@osu.edu

Sajedur R. Akanda

Department of Mechanical
and Aerospace Engineering,
The Ohio State University,
201 W. 19th Avenue,
Columbus, OH 43210
e-mail: akanda.2@buckeyemail.osu.edu

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 9, 2014; final manuscript received October 14, 2014; published online December 30, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(7), 072503 (Jul 01, 2015) (7 pages) Paper No: GTP-14-1542; doi: 10.1115/1.4029204 History: Received September 09, 2014; Revised October 14, 2014; Online December 30, 2014

An energy-based framework is developed to determine the fatigue strength parameters of the Basquin equation and the fatigue ductility parameters of the Manson–Coffin equation to predict high cycle fatigue (HCF) and low cycle fatigue (LCF) life of a steam turbine rotor base and weld materials. The proposed framework is based on assessing the complete energy necessary to cause fatigue failure of a material. This energy is considered as a fundamental material property and is known as the fatigue toughness. From the fatigue toughness and the experimentally determined fatigue lives at two different stress amplitudes, the cyclic parameters of the Ramberg–Osgood constitutive equation that describes the hysteresis stress–strain loop of a cycle are determined. Next, the coefficients and the exponents of the Basquin and the Manson–Coffin equations are computed from the fatigue toughness and the cyclic parameters of a material. The predicted fatigue life obtained from the present energy-based framework is found to be in a good agreement with the experimental data.

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Figures

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Fig. 1

A hysteresis loop representative of average plastic strain range Δɛ¯p and the average plastic energy w¯p to cause fatigue failure of a material in a fatigue test at stress range Δσ

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Fig. 2

The hysteresis loop of Fig. 1 shifted to the origin of the axis

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Fig. 3

Addition of elastic and plastic strain-life curves to produce total strain-life curve

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Fig. 4

Schematic diagram of a flat dogbone specimen for a monotonic tension test

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Fig. 5

Experimental setup of a monotonic tension test

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Fig. 6

Schematic diagram of a round dogbone specimen for a fatigue test

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Fig. 7

Experimental setup of a fatigue test

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Fig. 8

Engineering stress–strain curve of the WM

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Fig. 9

Cyclic plastic energy history of the WM at stress amplitude of 80% of yield strength. Test frequency was 0.1 Hz.

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Fig. 10

Hysteresis loops of the WM. Cycle 5 represents region 1, cycle 1501 represents region 2, and cycle 3059 represents region 3.

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Fig. 11

Experimental and predicted S–N curves of the WM

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Fig. 12

Cyclic plastic energy history of the BM at stress amplitude of 80% of yield strength. Test frequency was 0.1 Hz.

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Fig. 13

Experimental and predicted S–N curves of the BM

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