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Research Papers

A Model for the Determination of Residual Fatigue Life of a Nickel-Based Superalloy

[+] Author and Article Information
Duyi Ye1

Institute of Process Equipment and Control Engineering, Zhejiang University, Zheda Road 38, Hangzhou 310027, P.R.C.duyi̱ye@zju.edu.cn

Jinyang Zheng

Institute of Process Equipment and Control Engineering, Zhejiang University, Zheda Road 38, Hangzhou 310027, P.R.C.

1

Corresponding author.

J. Eng. Mater. Technol 130(3), 031010 (Jun 11, 2008) (8 pages) doi:10.1115/1.2931148 History: Received May 04, 2007; Revised November 01, 2007; Published June 11, 2008

In this paper, both the dissipation of the plastic-strain energy and the exhaustion of the static toughness during high-temperature low-cycle fatigue of GH4145/SQ superalloy were investigated. Together with the analysis of the microscopic aspects of the material, an energy-based damage mechanics model was developed for the prediction of the residual fatigue life of the high-temperature fastened parts in power plant. Experimental results show that the static toughness is a parameter that is highly sensitive to the fatigue damage process. The deterioration of the static toughness during fatigue process reveals the exhaustion of the materials’s ability to absorb energy, which is essentially associated with the irreversible energy dissipation process of the fatigue failure. Based on the dissipation of the plastic-strain energy and the exhaustion of the static toughness during fatigue, a damage variable is defined that is consistent with the fatigue damage mechanism. The variable is sensitive to the fatigue process and can be measured with a simple experimental procedure. A fatigue damage evolution equation is derived on the basis of Lemaitre’s potential of dissipation in the framework of continuum damage mechanics. Furthermore, an equation for the determination of the residual fatigue life is deduced. The fatigue damage mechanics model is verified by comparing the predicted results with the experimental observations. The fatigue damage mechanics model developed may provide a feasible approach to determining the residual fatigue life of the high-temperature fastened parts in power plant.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Photograph of a broken stud in a high-pressure inner cylinder

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Figure 2

SEM image of fracture surface of the broken stud showing striations along the crack propagation direction

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Figure 3

Hysteresis energy of GH4145/SQ superalloy as a function of number of cycles and strain amplitude at 538°C

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Figure 4

Typical dislocation patterns formed in GH4145/SQ superalloy prefatigued at 0.5% strain amplitude with (a) 0cycle, (b) 5cycles, (c) 2×103cycles, and (d) 4669cycles

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Figure 5

Variation of the static toughness of GH4145/SQ superalloy with the number of cycles at 538°C

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Figure 6

Typical fractographies of specimens prefatigued with different cyclic fraction (N∕Nf) at 0.5% strain amplitude followed by tensioning to fracture: (a) N∕Nf=0; (b) N∕Nf=0.1; (c) N∕Nf=0.1; (d) N∕Nf=0.4; (e) N∕Nf=0.8; (f) N∕Nf=1.0

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Figure 7

Correlation between the dissipation fraction of the plastic-strain energy and the exhaustion fraction of the static toughness during fatigue failure process of GH4145/SQ superalloy (11)

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Figure 8

Comparison of the damage evolution curves by Eq. 26 with experimental results

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Figure 9

Comparison of the residual fatigue-life between prediction and experiment

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