A Critical Examination of Stresses Within and Around Coatings

[+] Author and Article Information
Anthony P. Parker

Defence Academy of the United Kingdom,  Cranfield University, Swindon, SN6 8LA, United Kingdomtony_parker@tesco.net

Rolf R. de Swardt

 LIW Division of Denel, P.O. Box 7710, Pretoria, 0001, RSAfeadoctor@yahoo.com

J. Pressure Vessel Technol 128(2), 267-272 (Jan 08, 2006) (6 pages) doi:10.1115/1.2172615 History: Received November 18, 2005; Revised January 08, 2006

In many cases apparently complex interactions between a coating and a substrate may be reduced to a combination of two simple loading scenarios, namely, constant direct stress and linearly varying direct stress applied to the edges of the coating. Stresses within and around coatings are carefully and critically examined. Stress functions incorporating analytical limits are presented for the case of constant and linearly varying direct stress applied to the edge of a coating. Results provide accurate interfacial peeling and shear stresses, and were compared to equivalent finite element (FE) solutions. A technique is proposed for extrapolation of FE results that permits recovery of limiting values. Results were also compared to other recently published data. It is shown that inappropriate use of two sets of results may have produced erroneous interpretations. The particular case of a thin coating prone to craze-cracking is addressed. Direct stress at the free surface of a craze-cracked coating is a strong function of “island” size. In particular, the direct stress at the centerline of such a coating is compressive for island width of <4X coating thickness; this may help to explain the relative dimensions of craze cracking.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Basic coating-substrate geometry (top), basic loaded-edge geometry (bottom)

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Figure 2

Notched-infinite plate with constant tension on θ=0; stresses along θ=π∕2 for π∕2⩽β⩽2π

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Figure 3

Superposition of configurations used in formulation: (a) and (b) represent semi-infinite plates

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Figure 4

Coating interfacial stresses (constant stress loading)

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Figure 5

Superposition showing peeling stress is zero for tc=ts and a=b; (b) represents uniaxial tension, (c) represents anti-symmetric loading

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Figure 9

Thru-the-thickness coating direct stresses (superposed results, d∕tc=2)

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Figure 6

Superposition showing shear stress is zero for tc=ts and a=b: (b) represents pure bending, (c) represents symmetric loading

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Figure 7

Typical metallographic section of chromium-plated gun tube subjected to laser-pulse heating

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Figure 8

Coating interfacial and surface stresses with ts⪢tc (continuous lines-constant tensile stress loading, hatched line-superposed result)



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