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Technical Briefs

An Energy-Based Axial Isothermal- Mechanical Fatigue Lifing Procedure

[+] Author and Article Information
John Wertz, Onome Scott-Emuakpor, Tommy George, Charles Cross

Department of Mechanical and Aerospace Engineering,  The Ohio State University, Columbus, OH 43210 Air Force Research Laboratory, Wright-Patterson AFB, OH 45433

M.-H. Herman Shen1

Department of Mechanical and Aerospace Engineering,  The Ohio State University, Columbus, OH 43210shen.1@osu.edu Air Force Research Laboratory, Wright-Patterson AFB, OH 45433shen.1@osu.edu

1

Corresponding author.

J. Eng. Gas Turbines Power 134(2), 024502 (Dec 14, 2011) (5 pages) doi:10.1115/1.4004394 History: Received April 11, 2011; Revised May 22, 2011; Published December 14, 2011; Online December 14, 2011

An energy-based fatigue lifing procedure for the determination of full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature fatigue model, which states: the total strain energy density accumulated during both a monotonic fracture event and a fatigue process is the same material property. The energy-based axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy accrued during both a monotonic fracture process and a fatigue process at various elevated temperatures; and (3), the incorporation of the effect of temperature into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed in conjunction with the monotonic fracture curve testing procedure to produce fifteen fracture curves at four operating temperatures. The strain energy densities for these fracture curves were compared, leading to the assumption of constant monotonic fracture energy at operating temperatures below the creep activation temperature.

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Figures

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Figure 1

Temperature distribution study results

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Figure 2

Representative monotonic fracture curves at temperatures T0 , T1 , T2 , & T3 . (b) T1 , T2 , & T3 average strain energy density versus T0 strain energy density normal distribution

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Figure 3

(a) Effect of free-free boundary condition on engineering monotonic fracture curve (b) Monotonic fracture strain energy density (c) Effect of free-free boundary condition on fatigue hysteresis loop (d) Cyclic strain energy density

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