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Cracking During Nanoindentation and its Use in the Measurement of Fracture Toughness

Published online by Cambridge University Press:  21 February 2011

D. S. Harding ,
W. C. Oliver  and
G. M. Pharr
D. S. Harding
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
G. M. Pharr
Affiliation:
Department of Materials Science, Rice University, P.O. Box 1892, Houston, TX 77251
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Abstract

Results of an investigation aimed at developing a technique by which the fracture toughness of a thin film or small volume can be determined in nanoindentation experiments are reported. The method is based on the radial cracking which occurs when brittle materials are deformed by a sharp indenter such as a Vickers or Berkovich diamond. In microindentation experiments, the lengths of radial cracks have been found to correlate reasonably well with fracture toughness, and a simple semi-empirical method has been developed to compute the toughness from the crack lengths. However, a problem is encountered in extending this method into the nanoindentation regime with the standard Berkovich indenter in that there are well defined loads, called cracking thresholds, below which indentation cracking does not occur in most brittle materials. We have recently found that the problems imposed by the cracking threshold can be largely overcome by using an indenter with the geometry of the corner of a cube. For the cube-corner indenter, cracking thresholds in most brittle materials are as small as 1 mN (∼ 0.1 grams). In addition, the simple, well-developed relationship between toughness and crack length used for the Vickers indenter in the microindentation regime can be used for the cube-corner indenter in the nanoindentation regime provided a different empirical constant is used.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 356: Symposium B2 – Thin Films: Stresses and Mechanical Properties V , 1994 , 663
Copyright
Copyright © Materials Research Society 1995

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