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Spherical indentation analysis of stress relaxation for thin film viscoelastic materials

Cheneler, David; Mehrban, Nazia and Bowen, James (2013). Spherical indentation analysis of stress relaxation for thin film viscoelastic materials. Rheologica Acta, 52(7) pp. 695–706.

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The mechanical testing of thin layers of soft materials is an important but difficult task. Spherical indentation provides a convenient method to ascertain material properties whilst minimising damage to the material by allowing testing to take place in situ. However, measurement of the viscoelastic properties of these soft materials is hindered by the absence of a convenient yet accurate model which takes into account the thickness of the material and the effects of the underlying substrate. To this end, the spherical indentation of a thin layer of viscoelastic solid material is analysed. It is assumed that the transient mechanical properties of the material can be described by the generalised standard linear solid model. This model is incorporated into the theory and then solved for the special case of a stress relaxation experiment taking into account the finite ramp time experienced in real experiments. An expression for the force as a function of the viscoelastic properties, layer thickness and indentation depth is given. The theory is then fitted to experimental data for the spherical indentation of poly(dimethyl)siloxane mixed with its curing agent to the ratios of 5:1, 10:1 and 20:1 in order to ascertain its transient shear moduli and relaxation time constants. It is shown that the theory correctly accounts for the effect of the underlying substrate and allows for the accurate measurement of the viscoelastic properties of thin layers of soft materials.

Item Type: Journal Item
Copyright Holders: 2013 Springer-Verlag
ISSN: 1435-1528
Keywords: transient shear moduli; generalised standard linear solid model; stress relaxation; spherical indentation; soft solids
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Engineering and Innovation
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 43161
Depositing User: James Bowen
Date Deposited: 01 Jun 2015 09:51
Last Modified: 07 Dec 2018 18:32
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