Static and dynamic nanoindentation of polystyrene and poly(methyl methacrylate) coatings on glass substrate was studied during this project. An analytical determination of the reduced modulus profile of the coating/substrate system was developed, and the delamination behaviour of the coatings was investigated. Reduced moduli profiles showed an unexpected drop which was attributed to delamination and which has not previously been reported. The reduced modulus profiles of the coating/substrate systems were extracted and sigmoidal equations were fitted to them. It was found that the best fitting equation was a sigmoid with 2 adjustable parameters that control the slope of the sigmoid and its offset point. The variety of equations proposed in the literature was found to give less good fits. Those two parameters were found to be proportional to the coating thickness. Thus based on these results for a given coating thickness the reduced modulus profile of further PS & PMMA coatings of any thickness can be predicted without any testing, and the thickness of PS & PMMA coatings can be determined with just a few nanoindents. A novel way to determine when delamination of coatings occurred was found by plotting the variation of the final depth of indent against the contact depth. The delamination load, the depth at which it occurs and the radius of delamination can all be deduced. Delamination was found to reduce the measured coating/substrate modulus under static nanoindentation, this drop in modulus also indicated the indentation depth and load at which the delamination of coatings occurs. This drop in modulus was not present in dynamic nanoindentation. Nanoindentation tests were made with both Berkovich tip and a cube corner tip; it was found that the reduced modulus profile and delamination behaviour of the coating/substrate system was independent of the tip geometry. A comparison of the static and dynamic nanoindentation of PS and PMMA coatings showed that the reduced modulus profiles had very similar shapes in both methods used. A stress analysis was used to calculate the critical indent depth (her), maximum indentation depth at which the properties of the substrate goes unnoticed, for PS. It was shown that a glass substrate has a smaller critical indent depth than a PS one.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575472 |
| Date | January 2010 |
| Creators | Samson, Pierre |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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