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Can indentation technique measure unique elastoplastic properties?

Published online by Cambridge University Press:  31 January 2011

Ling Liu
Affiliation:
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, New York 10027-6699
Nagahisa Ogasawara
Affiliation:
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, New York 10027-6699
Norimasa Chiba
Affiliation:
Department of Mechanical Engineering, National Defense Academy, Hashirimizu, Yokosuka 239, Japan
Xi Chen*
Affiliation:
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, New York 10027-6699
*
a) Address all correspondence to this author.e-mail: xichen@civil.columbia.edu
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Abstract

Indentation is widely used to extract material elastoplastic properties from measured force-displacement curves. Many previous studies argued or implied that such a measurement is unique and the whole material stress-strain curve can be measured. Here we show that first, for a given indenter geometry, the indentation test cannot effectively probe material plastic behavior beyond a critical strain, and thus the solution of the reverse analysis of the indentation force-displacement curve is nonunique beyond such a critical strain. Secondly, even within the critical strain, pairs of mystical materials can exist that have essentially identical indentation responses (with differences below the resolution of published indentation techniques) even when the indenter angle is varied over a large range. Thus, fundamental elastoplastic behaviors, such as the yield stress and work hardening properties (functions), cannot be uniquely determined from the force-displacement curves of indentation analyses (including both plural sharp indentation and deep spherical indentation). Explicit algorithms of deriving the mystical materials are established, and we qualitatively correlate the sharp and spherical indentation analyses through the use of critical strain. The theoretical study in this paper addresses important questions of the application range, limitations, and uniqueness of the indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material constitutive properties.

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Copyright
Copyright © Materials Research Society 2009

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