Gas Turbines: Structures and Dynamics

An Energy-Based Axial Isothermal-Mechanical Fatigue Lifing Method

[+] Author and Article Information
John Wertz, Todd Letcher

Department of Mechanical and Aerospace Engineering,  The Ohio State University, Columbus, OH 43210

M.-H. Herman Shen1

Department of Mechanical and Aerospace Engineering,  The Ohio State University, Columbus, OH 43210shen.1@osu.edu

Onome Scott-Emuakpor, Tommy George, Charles Cross

 Air Force Research Laboratory, Wright-Patterson AFB, OH 45433


Corresponding author.

J. Eng. Gas Turbines Power 134(10), 102502 (Aug 17, 2012) (7 pages) doi:10.1115/1.4007121 History: Received June 20, 2012; Revised June 22, 2012; Published August 17, 2012; Online August 17, 2012

An energy-based fatigue lifing method for the determination of the 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 lifing model, which states: the total strain energy dissipated during both a quasi-static process and a dynamic (fatigue) process is the same material property. The 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 dissipated during both a quasi-static process and a dynamic process at elevated temperatures; and (3) the incorporation of the effect of thermal loading into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed to produce full-life and critical-life predictions as functions of temperature, which were shown to have an excellent correlation with experimental fatigue data. For the highest operating temperature, the axial IMF full-life prediction was compared to lifing predictions made by both the universal slopes and the uniform material law prediction and was found to be more accurate at an elevated temperature.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Validation of full-life and critical-life predictive capabilities, AL 6061-T6, R = −1 [15-16]

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Figure 2

Idealized schematic of quasi-static strain energy density [19]

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Figure 3

(a) Idealized schematic of dynamic strain energy density [11,19]; (b) experimental hysteresis loop

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Figure 4

Specimen design; dimensions in mm

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Figure 5

Thermal distribution pattern

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Figure 6

Representative quasi-static curves

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Figure 7

Experimental fatigue data

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Figure 8

Representative frequency sweep T3

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Figure 9

Normalized energy dissipation histories

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Figure 10

Prediction versus experimental data T0

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Figure 11

Prediction versus experimental data T1

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Figure 12

Prediction versus experimental data T3

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Figure 13

Dynamic curve-fit parameters versus temperature

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Figure 14

Prediction versus experimental data T2

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Figure 15

Axial IMF versus US and UML T3



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