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    Protocols are developed to assess viscoelastic moduli from unloading slopes in Berkovich nanoindentation across four orders of magnitude in time scale (0.01-100 s unloading time). Measured viscoelastic moduli of glassy polymers poly(methyl methacrylate), polystyrene, and polycarbonate follow the same trends with frequency (1/unloading time) as viscoelastic moduli generated from dynamic mechanical analysis and broadband viscoelastic spectroscopy but are 18-50% higher. Included in the developed protocols is an experimental method based on measured indent area to remove from consideration indents for which viscoplastic deformation takes place during unloading. Ancillary measurements of indent area and depth reveal no detectable (~1%) change in area between 200 s and 4.9 days following removal of indenter.

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    Jakes, Joseph E.; Lakes, Rod S.; Stone, Don S. 2012. Broadband nanoindentation of glassy polymers: Part I. Viscoelasticity. Journal of Materials Research. 27(2): 463-474.


    broadband nanoindentation, viscoelasticity, polymer

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