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Brinell Hardness Test
At the beginning of the 20th century. Johan August Brinell, a Swedish Metallurgist, proposed a rapid, standard method of measuring the hardness of metallic materials. The method as most commonly applied consists of indenting a surface with a 10 mm hard steel ball with a 3000 kg load for 30 seconds. The Brinell Hardness Number (BHN) is then measured by measuring the diameter of the indentation using a straightforward formula (or usually plucked off of a chart).
The load is reduced to 500kg for very soft materials, and the steel ball is replaced with tungsten carbide for very hard materials. Substantial section thicknesses are required to ensure that the test is "valid", that is, edge effects or gross section deformation remain negligible.
As a standardized test, the procedure is very useful in industrial settings, primarily as a quality-control tool. In common steels, as a rule-of-thumb, BHN 515 is approximately equal to the ultimate tensile strength.
The test is useless in the context of bicycles since almost no part of a modern bicycle would survive intact the effect of a 10 mm ball at 3000 kg and no part of a bicycle is sufficiently massive to ensure a "valid" test.
The BHN number, albeit a very useful tool in manufacturing, is not a satisfactory physical constant nor is it applied to design. Also, the BHN number is not reproducible under nonstandard ball diameters and loads unless geometric similitude is maintained.
Other hardness tests have largely replaced the Brinell test.
(This definition contributed by John Fox)
