Hardness Testing - Brinell Hardness

Topics Covered

Background

Brinell Hardness

Calculating Brinell Hardness

Advantages of Brinell Hardness Measurements

Background

The hardness of a material is defined as its resistance to another material penetrating its surface and is related to its wear resistance and strength. Higher hardness is related generally related to higher strength, which in turn is related to its structure. It is also a measure of a materials resistance to plastic deformation.

Brinell Hardness

The Brinell hardness test is suitable for a range of materials hardness’. Brinell hardness testing involves forcing a hardened steel ball (or a tungsten carbide ball for extremely hard materials) into the surface of the specimen. The ball usually has a diameter of 10mm and is pressed into the sample using a predetermined load dependent on the relative hardness of the material e.g. 500kg for softer metals and 3000kg for hard metals.

The load is applied for a defined time, usually 10-15 seconds and the impression diameter measured using a low power microscope.

Calculating Brinell Hardness

The hardness is then calculated as a ratio of the load to the curved surface of the impression using the equation:

where:

HB = Brinell hardness

F = load in kg

D = the diameter of the indenter in mm

D_i = impression diameter in mm

Advantages of Brinell Hardness Measurements

Due to the size of the indenter and the impression, the Brinell system is more indicative of the bulk material hardness compared to other techniques which test over a much smaller area and may in fact be measuring impurities or inclusions.

Primary author: AZoM.com