Roberts, S J; McCartney, L N (2003) Predicting steady state interface debonding in a multi-layered coated system under biaxial mechanical and thermal loading. NPL Report. MATC(A)144

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Abstract

In this report, it is described how the effective macroscopic strains may be predicted for an undamaged multi-layered system, consisting of isotropic materials and subjected to combined in-plane biaxial loading, out-of-plane bending and thermal residual stresses. The theory, extending an earlier approach developed for a single coating, makes use of the stress and deformation fields within the layered system and takes account of thermal stresses arising from mismatched elastic and thermal expansion coefficients. The model also takes into account anticlastic bend deformation. It is then shown how energy balance principles can be used to predict the steady state interfacial debonding associated with through-thickness cracks in a coated system.
Some sample predictions are made for debonding in regular multi-layered systems involving two types of coating material denoted by A and B. The debonding is assumed to occur at the interface of the multi-layered coating with the substrate made from a different material. For the first test case, the thicknesses of the A and B coatings are equal and held fixed while the number of AB layer pairs is increased. Thus, a variety of total coating thicknesses are considered and it is shown that the coating will debond more readily as the thickness of the coating system increases. For the second case, the total thickness of the multi-layer coating is held fixed but is subdivided into an increasing number of AB or BA layer pairs whose thickness decreases as the number of AB or BA layer pairs increase. The multi-layer coatings consisting of AB or BA layer pairs are also homogenised and applied as just a single coating having homogenised properties. Results suggest that at least 25 AB or BA layer pairs are needed in order that the homogenised coating behaves in a similar way to the discretely modelled AB or BA coating systems.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MATC(A)144
Subjects:	Advanced Materials Advanced Materials > Materials Modelling
Last Modified:	02 Feb 2018 13:16
URI:	http://eprintspublications.npl.co.uk/id/eprint/2817

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