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Indentation hardness tests compose the majority of processes used to determine material hardness, and can be divided into three classes: macro, micro and nanoindentation tests. [2] [3] Microindentation tests typically have forces less than 2 N (0.45 lb f). Hardness, however, cannot be considered to be a fundamental material property.
The typical test uses a 10 mm (0.39 in) diameter steel ball as an indenter with a 3,000 kgf (29.42 kN; 6,614 lbf) force. For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball. The indentation is measured and hardness calculated as:
A Rockwell hardness tester. The Rockwell hardness test is a hardness test based on indentation hardness of a material. The Rockwell test measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). [1]
The hardness is given by the equation above, relating the maximum load to the indentation area. The area can be measured after the indentation by in-situ atomic force microscopy, or by 'after-the event' optical (or electron) microscopy. An example indentation image, from which the area may be determined, is shown at right.
The Janka hardness test (English: / ˈ dʒ æ ŋ k ə /; [1] German:), created by Austrian-born American researcher Gabriel Janka (1864–1932), measures the resistance of a sample of wood to denting and wear. [citation needed] It measures the force required to embed an 11.28-millimeter-diameter (7 ⁄ 16 in
Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test. ASTM D2240 durometers allow for a measurement ...
Meyer's law is an empirical relation between the size of a hardness test indentation and the load required to leave the indentation. [1] The formula was devised by Eugene Meyer of the Materials Testing Laboratory at the Imperial School of Technology, Charlottenburg, Germany, circa 1908.
For the situation where the asperities on the two surfaces have a Gaussian height distribution and the peaks can be assumed to be spherical, [31] the average contact pressure is sufficient to cause yield when = where is the uniaxial yield stress and is the indentation hardness. [1]