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Effect of unloading strain rate on the elastic modulus of a viscoelastic solid determined by nanoindentation

Published online by Cambridge University Press:  01 March 2006

Naoki Fujisawa  and
Michael V. Swain
Naoki Fujisawa*
Affiliation:
School of Aerospace, Mechanical & Mechatronic Engineering, University of Sydney, Sydney NSW 2006, Australia
Michael V. Swain
Affiliation:
Biomaterials Unit, Department of Oral Sciences, School of Dentistry, University of Otago, Duniden, New Zealand; Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, United Dental Hospital, Surry Hills NSW 2010, Australia; and School of Aerospace, Mechanical & Mechatronic Engineering, University of Sydney, Sydney NSW 2006, Australia
*
a) Address all correspondence to this author. e-mail: n.fujisawa@usyd.edu.au
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Abstract

The elastic modulus of an amorphous polymer was investigated by nanoindentation using combinations of ten total penetration depths and three constant unload rates. This experimental design provided a range of unloading strain rates coexisting with a range of depths. The elastic modulus of the material was found to correlate strongly with the unloading strain rate, whereas its correlation with the indentation depth was statistically nonsignificant. Thus, the increase of elastic modulus that occurred with decreasing depth at each constant unload rate was merely due to the increasing unloading strain rate associated with the decreasing depth. The true depth dependence of a rate-dependent material can therefore be studied only by maintaining a constant unloading strain rate across the entire depth range. The implications of these results to the continuous stiffness measurement technique are considered.

Keywords

Elastic propertiesPolymer
Type
Articles
Information
Journal of Materials Research , Volume 21 , Issue 3 , March 2006 , pp. 708 - 714
Copyright
Copyright © Materials Research Society 2006

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References

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