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    Author(s): M.J. Wald; J.M. Considine; K.T. Turner
    Date: 2013
    Source: Experimental Mechanics; published online January 2013. pp. 11.
    Publication Series: Scientific Journal (JRNL)
    Station: Forest Products Laboratory
    PDF: Download Publication  (649.12 KB)

    Description

    Instrumented indentation is a technique that can be used to measure the elastic properties of soft thin films supported on stiffer substrates, including polymer films, cellulosic sheets, and thin layers of biological materials. When measuring thin film properties using indentation, the effect of the substrate must be considered. Most existing models for determining the properties of thin films from indentation measurements were developed for metal and dielectric films bonded to semiconductor substrates and have been applied to systems with film-substrate modulus ratios between 0.1 and 10. In the present work, flat punch indentation of a thin film either bonded to or in contact with a substrate is examined using finite element modeling. A broad range of film-substrate modulus ratios from 0.0001 to 1 are investigated. As the substrate is effectively rigid compared to the film when the film-substrate modulus ratio is less than 0.0001, the results are also useful for understanding systems with lower film-substrate modulus ratios. The effects of the contact radius, film thickness, elastic properties, and friction between the film and the substrate on the measured stiffness were quantified using finite element modeling in order to understand how the elastic properties of the film can be extracted from indentation measurements. A semi-analytical model was developed to describe the finite element modeling results and facilitate the use of the results to analyze experimental measurements. The model was val-idated through analysis of indentation measurements of thin polyethylene sheets that were supported on substrates of various stiffness.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Wald, M.J.; Considine, J.M.; Turner, K.T. 2013. Determining the elastic modulus of compliant thin films supported on substrates from flat punch indentation measurements. Experimental Mechanics.53: 931-941.

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    Keywords

    Indentation, thin films, finite elements, substrate effects, soft material

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