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Research Papers: Gas Turbines: Structures and Dynamics

A Fracture-Mechanics-Based Methodology for Fatigue Life Prediction of Single Crystal Nickel-Based Superalloys

[+] Author and Article Information
Srikant Ranjan

Mechanical and Aerospace Engineering Department, University of Florida, Gainesville, FL 32611-6300srikant@ufl.edu

Nagaraj K. Arakere1

Mechanical and Aerospace Engineering Department, University of Florida, Gainesville, FL 32611-6300nagaraj@ufl.edu

1

Corresponding author.

J. Eng. Gas Turbines Power 130(3), 032501 (Mar 26, 2008) (11 pages) doi:10.1115/1.2838990 History: Received October 16, 2006; Revised October 17, 2006; Published March 26, 2008

A comprehensive fracture-mechanics-based life prediction methodology is presented for fcc single crystal components based on the computation of stress intensity factors (SIFs), and the modeling of the crystallographic fatigue crack growth (FCG) process under mixed-mode loading conditions. The 3D finite element numerical procedure presented for computing SIFs for anisotropic materials under mixed-mode loading is very general and not just specific to fcc single crystals. SIFs for a Brazilian disk specimen are presented for the crack on the {111}) plane in the ⟨101⟩ and ⟨121⟩ directions, which represent the primary and secondary slip directions. Variation of SIFs as a function of thickness is also presented. Modeling of the crystallographic FCG behavior is performed by using the resolved shear stress intensity coefficient, Krss. This parameter is sensitive to the grain orientation and is based on the resolved shear stresses on the slip planes at the crack tip, which is useful in identifying the active crack plane as well as in predicting the crack growth direction. A multiaxial fatigue crack driving force parameter, ΔKrss, was quantified, which can be used to predict the FCG rate and, hence, life in single crystal components subject to mixed-mode fatigue loading.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Strain range versus cycles to failure (Nf) for LCF test data (PWA1493 AT 1200F) (4)

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Figure 2

Shear stress amplitude [Δτmax] versus cycles to failure (Nf)(4)

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Figure 3

Arrangement of quarter-point wedge elements along segment of crack front with nodal lettering convention (31)

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Figure 4

BD specimen with center crack lying in the (111) plane and oriented along the [101¯] direction

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Figure 5

BD specimen having center crack lying in the {111} slip plane and aligned along the [1¯21¯] direction

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Figure 6

KI versus 2a∕W ratio for [101¯] and [1¯21¯] orientations of BD specimen at ϕ=0deg

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Figure 7

KII versus 2a∕W ratio for [101¯] and [1¯21¯] orientations of BD specimen at ϕ=0deg

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Figure 8

KIII versus 2a∕W ratio for [101¯] and [1¯21¯] orientations of BD specimen at ϕ=0deg

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Figure 9

KI versus crack angle with force for [101¯] and [1¯21¯] orientations of BD specimen at 2a∕W=0.55

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Figure 10

KII versus crack angle with force for [101¯] and [1¯21¯] orientations of BD specimen at 2a∕W=0.55

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Figure 11

KIII versus crack angle with force for [101¯] and [1¯21¯] orientations of BD specimen at 2a∕W=0.55

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Figure 12

Half meshed model of BD specimen and the crack coordinate system

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Figure 13

Variation of SIF KI along BD specimen thickness at different crack angle for the [101¯] orientation

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Figure 14

Variation of SIF KII along BD specimen thickness at different crack angle for the [101¯] orientation

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Figure 15

Variation of SIF KI along BD specimen thickness at different crack angle for the [1¯21¯] orientation

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Figure 16

Variation of SIF KII along BD specimen thickness at different crack angle for the [1¯21¯] orientation

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Figure 17

Variation of SIF KIII along BD specimen thickness at different crack angle for the [101¯] orientation

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Figure 18

Variation of SIF KIII along BD specimen thickness at different crack angle for the [1¯21¯] orientation

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Figure 19

(a) Unsymmetry about midplane for crack oriented along {111} ⟨101⟩; (b) symmetry for crack lying along {111} ⟨121⟩

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Figure 20

Details of crack tip displacements and stresses at a distance r and θ from the crack tip in the crack coordinate system

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Figure 21

Burgers vector b is along slip direction ⟨011⟩ and slip plane direction is normal vector n along ⟨111⟩

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Figure 22

Trace of primary slip planes on the plane normal to the crack plane

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Figure 23

Crack growth on the {111} slip plane can be observed for BD specimen B(43)

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Figure 24

FCG rate of three specimens A, B, and C as a function of ΔKrss

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