Indentation hardness

This relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers.

Measuring mechanical properties for materials, for instance, of thin films, cannot be done using conventional uniaxial tensile testing.

[citation needed] Classical hardness testing usually creates a number which can be used to provide a relative idea of material properties.

The equation based definition of hardness is the pressure applied over the contact area between the indenter and the material being tested.

The results provide a lot of information about the mechanical behavior of the material, including hardness, e.g., elastic moduli and plastic deformation.

[4] Current technology can realize accurate force control in a wide range.

Though there are practical conversion tables for hard steels, for example, some materials show qualitatively different behaviors under the various measurement methods.

The methodologies involved are often grouped under the term Indentation plastometry, which is described in a separate article.

The term "microhardness" has been widely employed in the literature to describe the hardness testing of materials with low applied loads.

Microindentation tests typically have forces of 2 N (roughly 200 gf) and produce indentations of about 50 μm.

Due to their specificity, microhardness testing can be used to observe changes in hardness on the microscopic scale.

This elongated pyramid creates a shallow impression, which is beneficial for measuring the hardness of brittle materials or thin components.

Both the Knoop and Vickers indenters require polishing of the surface to achieve accurate results.

[citation needed] Scratch tests at low loads, such as the Bierbaum microcharacter test, performed with either 3 gf or 9 gf loads, preceded the development of microhardness testers using traditional indenters.

The first reference to the Vickers indenter with low loads was made in the annual report of the National Physical Laboratory in 1932.

[citation needed] There is some disagreement in the literature regarding the load range applicable to microhardness testing.

Thus at low loads, small measurement errors will produce large hardness deviations.

Also, in the vertical portion of the curves, small measurement errors will produce large hardness deviations.

However, it has been experimentally determined through "strainless hardness tests" that the effect is minimal with smaller indentations.

Indentation hardness on the other hand is constrained in three dimensions which prevent shear from dominating the failure.