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Materials 2018, 11(4), 497; https://doi.org/10.3390/ma11040497

FEM Modeling of In-Plane Stress Distribution in Thick Brittle Coatings/Films on Ductile Substrates Subjected to Tensile Stress to Determine Interfacial Strength

1
Aerospace Research Institute of Materials & Processing Technology, Beijing 100076, China
2
Research Center for Composite Materials, School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
3
Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA
*
Author to whom correspondence should be addressed.
Received: 12 February 2018 / Revised: 19 March 2018 / Accepted: 23 March 2018 / Published: 27 March 2018
(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)
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Abstract

The ceramic-metal interface is present in various material structures and devices that are vulnerable to failures, like cracking, which are typically due to their incompatible properties, e.g., thermal expansion mismatch. In failure of these multilayer systems, interfacial shear strength is a good measure of the robustness of interfaces, especially for planar films. There is a widely-used shear lag model and method by Agrawal and Raj to analyse and measure the interfacial shear strength of thin brittle film on ductile substrates. The use of this classical model for a type of polymer derived ceramic coatings (thickness ~18 μm) on steel substrate leads to high values of interfacial shear strength. Here, we present finite element simulations for such a coating system when it is subjected to in-plane tension. Results show that the in-plane stresses in the coating are non-uniform, i.e., varying across the thickness of the film. Therefore, they do not meet one of the basic assumptions of the classical model: uniform in-plane stress. Furthermore, effects of three significant parameters, film thickness, crack spacing, and Young’s modulus, on the in-plane stress distribution have also been investigated. ‘Thickness-averaged In-plane Stress’ (TIS), a new failure criterion, is proposed for estimating the interfacial shear strength, which leads to a more realistic estimation of the tensile strength and interfacial shear strength of thick brittle films/coatings on ductile substrates. View Full-Text
Keywords: polymer derived ceramic coatings; FEM modelling; thick films; in-plane Stress; interfacial shear strength; crack density polymer derived ceramic coatings; FEM modelling; thick films; in-plane Stress; interfacial shear strength; crack density
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wang, K.; Zhang, F.; Bordia, R.K. FEM Modeling of In-Plane Stress Distribution in Thick Brittle Coatings/Films on Ductile Substrates Subjected to Tensile Stress to Determine Interfacial Strength. Materials 2018, 11, 497.

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