Spherical indentation analysis of stress relaxation for thin film viscoelastic materials

Cheneler, David and Mehrban, Nazia and Bowen, James (2013) Spherical indentation analysis of stress relaxation for thin film viscoelastic materials. Rheologica Acta, 52 (7). pp. 695-706. ISSN 0035-4511

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Abstract

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 Article
Journal or Publication Title:
Rheologica Acta
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/3100/3104
Subjects:
ID Code:
67469
Deposited By:
Deposited On:
08 Nov 2013 15:15
Refereed?:
Yes
Published?:
Published
Last Modified:
01 Apr 2020 03:23