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Special Issue Honoring Professor Fazil Erdogan’s Contributions to Mixed Boundary Value Problems of Inhomogeneous and Functionally Graded Materials

Delamination of Compressively Stressed Orthotropic Functionally Graded Material Coatings Under Thermal Loading

[+] Author and Article Information
Bora Yıldırım1

Mechanical Engineering Department, Hacettepe University, 06800 Ankara, Turkeyboray@hacettepe.edu.tr

Suphi Yılmaz

 Aselsan Inc., 06172 Ankara, Turkey

Suat Kadıoğlu

Mechanical Engineering Department, Middle East Technical University, 06531 Ankara, Turkey

1

Corresponding author.

J. Appl. Mech 75(5), 051106 (Jul 11, 2008) (10 pages) doi:10.1115/1.2936239 History: Received May 30, 2007; Revised September 26, 2007; Published July 11, 2008

The objective of this study is to investigate a particular type of crack problem in a layered structure consisting of a substrate, a bond coat, and an orthotropic functionally graded material coating. There is an internal crack in the orthotropic coating layer. It is parallel to the coating bond-coat interface and perpendicular to the material gradation of the coating. The position of the crack inside the coating is kept as a variable. Hence, the case of interface crack is also addressed. The top and bottom surfaces of the three layer structure are subjected to different temperatures and a two-dimensional steady-state temperature distribution develops. The case of compressively stressed coating is considered. Under this condition, buckling can occur, the crack can propagate, and the coating is prone to delamination. To predict the onset of delamination, one needs to know the fracture mechanics parameters, namely, Mode I and Mode II stress intensity factors and energy release rates. Hence, temperature distributions and fracture parameters are calculated by using finite element method and displacement correlation technique. Results of this study present the effects of boundary conditions, geometric parameters (crack length and crack position), and the type of gradation on fracture parameters.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

The geometry of the embedded crack problem

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Figure 2

Nodal displacements in x2 and x1 directions near the crack tip

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Figure 3

Plane 2 elements and modeling of crack tip region

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Figure 4

Close-up view of the crack tip region

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Figure 5

Deformed mesh of the FGM, bond coat and substrate system (a) just before buckling, ΔT∕T0=0.8; (b) just after buckling, ΔT∕T0=0.88; (c) at maximum temperature difference, ΔT∕T0=3.34 (a∕h1=20, MR1 material, true scale, lateral rotation is prevented)

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Figure 6

Deformed shape of the FGM, bond coat and substrate system: (a) overall deformation response at maximum temperature difference, ΔT∕T0=3.34; (b) close-up view of crack region (a∕h1=20 and MR1 material, true scale, lateral rotation is allowed)

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Figure 7

Displacement of the midpoint of upper crack surface (a∕h1=20 and MR1 material)

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Figure 8

Normalized SIFs, for buckling and bowing cases (a∕h1=20 and MR1 material)

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Figure 9

Normalized strain energy release rates for buckling and bowing cases (a∕h1=20 and MR1 material)

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Figure 10

Normalized Mode I and Mode II SIFs for crack at the bond coat-FGM interface, a∕h1=20

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Figure 11

Normalized energy release rate values for crack at the bond coat-FGM interface, a∕h1=20

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Figure 12

Normalized Mode I and Mode II SIFs for crack at the bond coat-FGM interface, MR1 material properties for FGM

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Figure 13

Normalized energy release rate values for crack at the bond coat-FGM interface, MR1 material properties for FGM

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Figure 14

Normalized Mode I and Mode II SIFs for changing crack heights, a∕h1=20 and MR1 material properties

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Figure 15

Normalized energy release rate values for changing crack heights, a∕h1=20 and MR1 material properties

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