Abstract
I AM greatly interested in the letter on “A Curious Feature in the Hardness of Metals,” by Mr. Hugh O'Neill and Dr. F. C. Thompson, which appears at p. 773 of NATURE of December 9, for in my paper “Experiments with Clay in its relation to Piles,” read before the Society of Engineers on March 10, 1919, will be found an account of the “pressure of fluidity” of clay. Briefly this may be described thus. When a horizontal disc resting on clay is gradually loaded it slowly sinks into the clay, each increment of load producing a corresponding increment of penetration, but when the load on the disc reaches a certain critical value the disc continues to sink at about ten times the speed without any further increase of the load. This load divided by the area Of the disc I have called the pressure of fluidity of the clay. This quantity has been found, within a considerable range, to be independent of the area of the disc used for its determination. The only factor upon which it depends, in the case of the London clay used, is the percentage of water in the clay, and by this it is very greatly affected, as will be seen from the following equations, which fit the results closely within the ranges stated, and the table below.
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ACKERMANN, A. Experiments on Hardness and Penetration. Nature 111, 17 (1923). https://doi.org/10.1038/111017a0
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DOI: https://doi.org/10.1038/111017a0
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