Abstract
RECENTLY, S. Tolansky and V. R. Howes1 published some data on indentation compression strength with a diamond ball (0.39 mm. radius) on differently orientated diamond faces. They obtained values for the pressure which caused cracking on different diamond faces ranging from 1.2 to 1.8 × 1011 dyne-cm.−2 (1,200–1,800 kgm./mm.2). By comparing these values with those quoted in the literature it appears that they are extremely low : F. Auerbach2, absolute hardness of diamond 2,200 kgm./mm.2; Knoop, hardness3 of diamond 6,500–8,500 kgm./mm.2; Russian tests with triangular pyramids4 and my own tests5 with the same type of indenter indicated hardnesses greater than 14,000 kgm./mm.2. Recent tests with double cone indenters (radius 2 mm., included angle 154°) showed that diamond surfaces could be loaded to well over 3,000 kgm./mm.2 without showing any form of cracks even when investigated with the electron microscope (by courtesy of Mr. M. Seal, Cambridge).
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References
Howes, V. R., and Tolansky, S., Proc. Roy. Soc., A, 230, 294 (1955).
Auerbach, F., Smithsonian Report, 4, 207 (1891).
Knoop, Indust. Diamond Rev., 4, 103 (1944).
Khrushchov, M. M., and Berkovich, E. S., Zavodskaya Lab., (2), 193 (1950); Indust. Diamond Rev., 11, 42 (1951).
Grodzinski, P., and Stern, W., Indust. Diamond Rev., 11, 48 (1951).
Hertz, H., “Miscellaneous Papers”, (London, 1896).
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GRODZINSKI, P. Indentation Hardness of Diamond. Nature 177, 1228 (1956). https://doi.org/10.1038/1771228a0
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DOI: https://doi.org/10.1038/1771228a0
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