Hunt, R A; McCartney, L N (2001) Use of models to predict deformation during the elastic nano-indentation of coatings. NPL Report. MATC(A)45

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Abstract

This report describes progress that has been made with the development of a methodology to estimate, from nano-indentation tests, the elastic properties of coatings whose thickness are in the micron range. The report summarises the results of new work that has been carried out, and intercomparison results that formed part of the international INDICOAT project.
The basis and performance of an NPL developed hybrid model for predicting the indentation behaviour for coated systems is described. The model uses analytical techniques supplemented with FEA analyses for flat circular punches. The hybrid approach was developed to avoid the problem of having to deal with the moving contact boundary during loading. The methodology enables the application of the analysis to any axisymmetric indenter shape, and leads to predictions of the effective indenter modulus that are independent of indenter shape and coating thickness.
For elastic axisymmetric deformation, the load-penetration curves and surface profiles predicted in the INDICOAT project, by FEA modelling, and various analytical approaches including the NPL hybrid model, are in agreement indicating that these models are consistent with one another. The Gao et al model developed for flat circular punches is, however, shown to be inaccurate when compared to FEA solutions.
The analysis of the elastic behaviour of a pre-dented coated sample (using a spherical indenter) has shown that the contact is not Hertzian implying that the stress concentration effect of the indent is having a significant effect on load-penetration behaviour. This indicates that the Oliver and Pharr analysis, conventionally used to extract the effective modulus from the unloading part of elastic=plastic load penetration curves, has no sound scientific basis.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MATC(A)45
Subjects:	Advanced Materials Nanoscience Advanced Materials > Materials Modelling Nanoscience > Nano-Materials
Last Modified:	02 Feb 2018 13:17
URI:	http://eprintspublications.npl.co.uk/id/eprint/2084

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