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Research Papers

Modeling Effects of Compliant Coatings on HCF Resistance of Primary Inclusions in High Strength Steels

[+] Author and Article Information
Rajesh Prasannavenkatesan

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

David L. McDowell1

George W. Woodruff School of Mechanical Engineering, and School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405david.mcdowell@me.gatech.edu

Gregory B. Olson

Department of Materials Science and Engineering, Robert R. McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208-3108; Questek Innovations LLC, Evanston, IL 60201

Herng-Jeng Jou

 Questek Innovations LLC, Evanston, IL 60201

1

Corresponding author.

J. Eng. Mater. Technol 131(1), 011012 (Dec 22, 2008) (6 pages) doi:10.1115/1.3030943 History: Received June 18, 2008; Revised October 14, 2008; Published December 22, 2008

Nucleation of fatigue cracks at nonmetallic primary inclusions in high cycle fatigue of martensitic steel is computationally investigated. We explore the capabilities of an elastic interphase material adhered to the inclusion surface to alter the driving force for fatigue crack nucleation in the matrix. By varying the elastic stiffness of the encapsulating interphase, the stresses and cyclic plastic strains are examined in the matrix in the proximity of a partially debonded inclusion, a worst case scenario for nucleation. The matrix is modeled as elastic-plastic with pure kinematic hardening expressed in a hardening minus dynamic recovery format. The inclusion and interphase are modeled as isotropic linear elastic. An idealized spherical, homogeneous inclusion is considered to facilitate parametric study. A nonlocal average value of the maximum plastic shear strain amplitude was used in a modified form of the Fatemi–Socie parameter in the proximity of inclusions as a fatigue indicator parameter to facilitate comparative parametric study of potency for crack nucleation.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic showing a partially debonded elastic inclusion with coating embedded in an elastoplastic matrix subjected to cyclic loading

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Figure 2

Cross section of the FE mesh through the center of the inclusion, showing refinement close to the inclusion. Cyclic loading is in the Z direction.

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Figure 3

Cross-sectional views of the 3D section with embedded inclusion elaborating on the debonded surface, boundary conditions for uniaxial loading, and cyclic loading direction. Views across (a) XY, (b) XZ, and (c) YZ cutting planes through the center of the inclusion.

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Figure 4

Variation in the FS parameter with applied strain range and strain ratio

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Figure 5

Variation in the normalized nonlocal FS parameter with ζ (normalized by respective values at ζ=1)

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Figure 6

Elastic stiffness ratio versus crack nucleation life for several applied strain ranges and strain ratios (Rε=0 and −1)

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