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Effects of Residual Stress on the Measurement of Hardness and Elastic Modulus using Nanoindentation

Published online by Cambridge University Press:  22 February 2011

G.M. Pharr ,
T.Y. Tsui ,
A. Bolshakov  and
W.C. Oliver
G.M. Pharr
Affiliation:
Department of Materials Science, Rice University, P.O. Box 1892, Houston, TX 77251
T.Y. Tsui
Affiliation:
Department of Materials Science, Rice University, P.O. Box 1892, Houston, TX 77251
A. Bolshakov
Affiliation:
Department of Materials Science, Rice University, P.O. Box 1892, Houston, TX 77251
W.C. Oliver
Affiliation:
Nano Instruments, Inc., P.O. Box 14211, Knoxville, TN 37914
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Abstract

The effects of stress on the measurement of hardness and elastic modulus in aluminum alloy 8009 have been studied experimentally and by finite element simulation. The experiments were performed by making a linear array of nanoindentations on the side of a stressed bend bar, sampling regions of high uniaxial tension, high uniaxial compression, and a variety of stresses in between. When analyzed according to standard methods, the nanoindentation data reveal a decrease in both hardness and modulus with increasing stress from compression to tension. While the decrease in hardness is consistent with previous observations made in conventional hardness testing, the modulus decrease was unexpected. Finite element simulation revealed that the drops in hardness and modulus are not real, but occur because the procedure for determining contact area from the nanoindentation load-displacement data does not account for pileup around the indentation. The finite element simulation shows that large compressive stresses promote pileup while tensile stresses reduce it, and this must be properly accounted for if accurate hardnesses and moduli are to be obtained. Experimental results are presented which further support this point of view.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 338: Symposium – Materials Reliability in Microelectronics IV , 1994 , 127
Copyright
Copyright © Materials Research Society 1994

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References

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