Monclus, M A; Jennett, N M (2011) In search of validated measurements of the properties of visco-elastic materials by indentation with sharp indenters. Philos. Mag., 91 (7-9). pp. 1308-1328.

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Abstract

Industrial requirement for local polymer properties and properties of small volumes as input to part design (e.g. micro-mouldings, packaging, coatings, composite interfaces') is driving an urgent demand for validated high-resolution methods to characterise viscoelastic materials. Here, we develop two instrumented indentation methods and compare the data obtained with results obtained on the same materials by dynamic mechanical analysis and uniaxial tensile testing. We find sufficient agreement to suggest that a route to validated measurement methods is available. We use simple force-controlled 'force-increase ramp and hold' indentation creep experiments to obtain the modulus and viscoelastic properties of three commercial polymers [two photo stress materials and polyoxymethylene (POM)]. A creep analysis based on conical-pyramidal elastic-viscoelastic correspondence [ ] and a three element, standard linear solid (SLS) model gives an output of two elastic moduli (E1 and E2) and a viscosity (h). Results obtained using various maximum forces (Pmax) and two indenter geometries [pyramidal (Berkovich) and conical (0.6 um tip radius)] are compared with dynamic indentation (D.I) and dynamic mechanical analysis (DMA) measurements at 40 Hz on the same materials. Agreement for all materials is very good at low applied forces, where elastic deformation dominates. The same SLS creep model is used to fit uniaxial tensile data from the POM sample. The modulus obtained agrees both with the tensile result and the values obtained by indentation creep and D.I. We also show how E1, E2 andh can be used to mathematically calculate loss and storage modulus values for all frequencies without further measurement.

Item Type:	Article
Keywords:	Indentation, Polymers, Viscoelastic Properties, Creep Analysis
Subjects:	Advanced Materials Advanced Materials > Surface Engineering
Identification number/DOI:	10.1080/14786435.2010.504197
Last Modified:	02 Feb 2018 13:14
URI:	http://eprintspublications.npl.co.uk/id/eprint/4936

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