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Viscoelastic effects during unloading in depth-sensing indentation

Published online by Cambridge University Press:  31 January 2011

A. H. W. Ngan  and
B. Tang
A. H. W. Ngan
Affiliation:
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China
B. Tang
Affiliation:
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China
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Abstract

With polypropylene as a prototype viscoelastic material at room temperature, it was found that a “nose” may appear in the unloading segment of the load–displacement curve during nanoindentation when the holding time at peak load is short and/or the unloading rate is small, and when the peak load is high enough. The load at which the nose appears was also found to decrease linearly with decreasing unloading rate. A linear viscoelasticity analysis was performed to interpret this effect. The analysis predicts a linear variation between the nose load and the unloading rate, and the slope of such a linear variation is also shown to be proportional to the viscosity parameter of the material. Thus, by measuring the slope of the nose-load versus unloading rate plot at a given temperature, the viscosity parameter of the specimen can be found. This is a new way of measuring the viscosity parameter of a material in addition to the existing method of force modulation and noting the frequency response of the displacement.

Type
Articles
Information
Journal of Materials Research , Volume 17 , Issue 10 , October 2002 , pp. 2604 - 2610
Copyright
Copyright © Materials Research Society 2002

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References

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