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I'd like to know about the constant in knoop's hardness formula. where it from ?Ulisses Bastos Campregher
- PortoAlegre, RS, Brazil
Hardness scales are very very interesting. I'm sure you know about the Mohs scale that classifies all mineral compounds from 1 - 10. There is also a modified Mohs scale that adds a .5 to the same classification. The Knoop scale takes these same minerals and gives them numerical values of 1 - 7000. There are about a dozen other scales and a lot of these are just variations of the Mohs scale but the contact stylus is different or the means to measure the indent is different. I have a book coming out soon that covers this subject.
I assume you refer to the 14229 number found in ASTM E 384, among other sources. This is the constant that relates the projected area of the indentation to the length of the long diagonal, which is what you measure. I believe that Paragraph 3.3 in the ASTM specification covers the derivation fairly well.
I hope this helps!
metallurgist - E. Aurora, New York