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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Comparison Between Linear and Nonlinear Fracture Mechanics Analysis of Experimental Data for the Ductile Superalloy Haynes 230

[+] Author and Article Information
Daniel Ewest

Siemens Industrial Turbomachinery AB,
Finspång SE-61283, Sweden
e-mail: Daniel.Ewest@Siemens.com

Per Almroth

Siemens Industrial Turbomachinery AB,
Finspång SE-61283, Sweden
e-mail: Per.Almroth@Siemens.com

Björn Sjödin

Siemens Industrial Turbomachinery AB,
Finspång SE-61283, Sweden
e-mail: Bjorn.Sjodin@Siemens.com

Daniel Leidermark

Division of Solid Mechanics,
Linköping University,
Linköping SE-58183, Sweden
e-mail: Daniel.Leidermark@liu.se

Kjell Simonsson

Division of Solid Mechanics,
Linköping University,
Linköping SE-58183, Sweden
e-mail: Kjell.Simonsson@liu.se

1Industry doctoral student at Linköping University.

Contributed by the Manufacturing Materials and Metallurgy Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 19, 2015; final manuscript received August 25, 2015; published online November 17, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(6), 062101 (Nov 17, 2015) (7 pages) Paper No: GTP-15-1413; doi: 10.1115/1.4031712 History: Received August 19, 2015; Revised August 25, 2015

With increasing use of renewable energy sources, an industrial gas turbine is often a competitive solution to balance the power grid. However, life robustness approaches for gas turbine components operating under increasingly cyclic conditions are a challenging task. Ductile superalloys, as Haynes 230, are often used in stationary gas turbine hot parts such as combustors. The main load for such components is due to nonhomogeneous thermal expansion within or between parts. As the material is ductile, there is considerable redistribution of stresses and strains due to inelastic deformations during the crack initiation phase. Therefore, the subsequent crack growth occurs through a material with significant residual stresses and strains. In this work, fatigue crack propagation experiments, including the initiation phase, have been performed on a single edge notched specimen under strain controlled conditions. The test results are compared to fracture mechanics analyses using the linear ΔK and the nonlinear ΔJ approaches, and an attempt to quantify the difference in terms of a life prediction is made. For the tested notched geometry, material, and strain ranges, the difference in the results using ΔKeff or ΔJeff is larger than the scatter seen when fitting the model to the experimental data. The largest differences can be found for short crack lengths, when the cyclic plastic work is the largest. The ΔJ approach clearly shows better agreement with the experimental results in this regime.

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References

Figures

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Fig. 6

Fatigue crack growth rates versus ΔJeff versus crack growth rate, from Ref. [17]

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Fig. 5

Schematic force–displacement curve, with opening force indicated and integration area (grey) for the ΔJeff-integral

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Fig. 3

Stress–strain evolution for case D1 and the change in slope is due to crack closure

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Fig. 2

Visual crack length versus number of cycles to failure

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Fig. 1

The test specimen geometry, units given in mm

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Fig. 7

ΔJeff and ΔJeffK versus crack length. (a) Case D1, Rε = 0 and Δε = 0.750%, (b) Case D2, Rε − ∞ and Δε = 0.600%, (c) Case D3, Rε = 0 and Δε = 0.568%, (d) Case D4, Rε = 0 and Δε = 0.407% and (e) Case D5, Rε = 0 and Δε = 0.300%.

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Fig. 8

Calculated crack length with ΔJeff and ΔKeff approaches with visual crack length from test versus number of cycles. (a) Case D1, Rε = 0 and Δε = 0.750%, (b) Case D2, Rε − ∞ and Δε = 0.600%, (c) Case D3, Rε = 0 and Δε = 0.568%, (d) Case D4, Rε = 0 and Δε = 0.407% and (e) Case D5, Rε = 0 and Δε = 0.300%.

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Fig. 9

Calculated da/dN and crack length with ΔJeff and ΔKeff approaches with test results. (a) Case D1, Rε = 0 and Δε = 0.750%, (b) Case D2, Rε − ∞ and Δε = 0.600%, (c) Case D3, Rε = 0 and Δε = 0.568%, (d) Case D4, Rε = 0 and Δε = 0.407% and (e) Case D5, Rε = 0 and Δε = 0.300%.

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Fig. 4

Schematic stress–strain loop, indicating the stress–strain states used to calculate ΔJ

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