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Measurement of the fracture toughness of CVD-grown ZnS using a miniaturized disk-bend test

Published online by Cambridge University Press:  31 January 2011

Jimin Zhang  and
Alan J. Ardell
Jimin Zhang
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, California 90024
Alan J. Ardell
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, California 90024
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Abstract

Novel apparatus and methodology have been developed for measuring the fracture toughness of ceramics using small disk-shaped samples 3 mm in diameter. The method involves the Vickers indentation of specimens ranging in thickness from 300 to 700 μm, and testing them in a ring-on-ring bending mode. Experiments on ZnS grown by chemical vapor deposition (CVD) have been used to evaluate the technique. The apparent fracture toughness of this material increases with crack length (R-curve behavior). This behavior is analyzed using established equations in conjunction with a new graphical method that obviates the need for measuring the apparent toughness of samples containing very large cracks. The fracture toughness at “infinite” crack length, 0.86 ± 0.08 MPa · m1/2, is in very good agreement with the values obtained by conventional methods. The effect of sample size on the accuracy of the results is thoroughly discussed. The thickness, t, of the sample should exceed by a factor of ten the initial crack length produced by the indentation. Also, since samples are tested at various indentation loads, P, the ratio of their thicknesses should be chosen to satisfy the condition t ∝ P2/3. The importance of several parameters in the design of the apparatus is also discussed.

Type
Articles
Information
Journal of Materials Research , Volume 6 , Issue 9 , September 1991 , pp. 1950 - 1957
Copyright
Copyright © Materials Research Society 1991

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