Brinell scale


The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.

History

Proposed by Swedish engineer Johan August Brinell in 1900, it was the first widely used and standardised hardness test in engineering and metallurgy. The large size of indentation and possible damage to test-piece limits its usefulness. However, it also had the useful feature that the hardness value divided by two gave the approximate UTS in ksi for steels. This feature contributed to its early adoption over competing hardness tests.

Test details

The typical test uses a diameter steel ball as an indenter with a 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:
where:
Brinell hardness is sometimes quoted in megapascals; the Brinell hardness number is multiplied by the acceleration due to gravity, 9.80665 m/s2, to convert it to megapascals.
The BHN can be converted into the ultimate tensile strength, although the relationship is dependent on the material, and therefore determined empirically. The relationship is based on Meyer's index from Meyer's law. If Meyer's index is less than 2.2 then the ratio of UTS to BHN is 0.36. If Meyer's index is greater than 2.2, then the ratio increases.
BHN is designated by the most commonly used test standards as HBW. In former standards HB or HBS were used to refer to measurements made with steel indenters.
HBW is calculated in both standards using the SI units as
where:

Common values

When quoting a Brinell hardness number, the conditions of the test used to obtain the number must be specified. The standard format for specifying tests can be seen in the example "HBW 10/3000". "HBW" means that a tungsten carbide ball indenter was used, as opposed to "HBS", which means a hardened steel ball. The "10" is the ball diameter in millimeters. The "3000" is the force in kilograms force.
The hardness may also be shown as XXX HB YYD2. The XXX is the force to apply on a material of type YY. Thus a typical steel hardness could be written: 250 HB 30D2. It could be a maximum or a minimum.
symbolDiameter of Indenter
mm		F/D2Test force
N/kgf
HBW 10/3000103029420
HBW 10/1500101514710
HBW 10/100010109807

Advantages

It can be used to test for non-homogeneous materials. Brinel provides the opportunity to test using different forces and different indenters. The testing process is non-destructive.

Standards