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Research Papers

A Slip Damping Model for Plasma Sprayed Ceramics

[+] Author and Article Information
Peter J. Torvik

 Air Force Institute of Technology, 1866 Winchester Road, Xenia, OH 45385torvik@att.net

J. Appl. Mech 76(6), 061018 (Jul 27, 2009) (8 pages) doi:10.1115/1.3132182 History: Received July 18, 2008; Revised April 03, 2009; Published July 27, 2009

Ceramic materials applied by air plasma spray are used as components of thermal barrier coatings. As it has been found that such coatings also dissipate significant amounts of energy during vibration, they can also contribute to reducing the amplitude of resonant vibrations. In order to select a coating material for this purpose, or to adjust application parameters for increased dissipation, it is important that the specific mechanism, by which such dissipation occurs, be known and understood. It has been suggested that the dissipative mechanism in air plasma sprayed coatings is friction, along interfaces arising from defects between and within the “splats” created during application. An analysis, similar to that for the dissipation in a lap joint, is developed for an idealized microstructure characteristic of such coatings. A measure of damping (loss modulus) is extracted, and the amplitude dependence is found to be similar to that observed with actual coating materials. A critical combination of parameters is identified, and variations within the microstructure are accounted for by representing values through a distribution. The effective or average value of the storage (Young’s) modulus is also developed, and expressed in terms of the parameters of the microstructure. The model appears to provide a satisfactory analytical representation of the damping and stiffness of these materials.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 4

Unit cell for material with microslip (a) location of unit cell and (b) detail of unit cell

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Figure 5

Distribution of axial forces; loaded and unloading (a) constituent 1 and (b) constituent 2

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Figure 6

Load distribution in constituent 2, before and during reloading

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Figure 7

Hysteresis loops with partial slip (a) initial loading; fully reversed load and (b) partially reversed loads

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Figure 8

Hysteresis loop for loading beyond full slip

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Figure 9

Loss modulus, single cell

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Figure 10

Influence of distribution parameter on loss modulus (a) computed from a slip model, and (b) observed, titania-alumina ceramic

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Figure 11

Storage modulus

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Figure 1

Force-displacement hysteresis loop with partial slip

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Figure 2

Microstructure of plasma sprayed MgAl spinel (by Shipton and Patsias (10); used with permission)

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Figure 3

Loss modulus for ceramic-coatings: (a) plasma sprayed titania-alumina and (b) 8% yttria stabilized zirconia

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