What is Brinell Hardness?

The Brinell hardness test is used to determine the hardness of materials in relationship to other materials along a consistent scale, so that scientists can both replicate results and have a frame of reference for the given hardness of a material. During the test, a small steel or carbide ball is forced into the material of unknown hardness with a set amount of pressure. The area of the resulting indentation is measured, and a mathematical formula is applied to yield a Brinell hardness number. Brinell hardness is commonly used in reference to metals and alloys, although it can refer to other materials as well.

The test is named for Johan August Brinell, a Swedish engineer who lived from 1849-1925. His work with metals led to several discoveries including the Brinell hardness test. His name is also attached to brinelling, an engineering term which refers to the point at which a metal will fail as a result of load and impact. He developed Brinell hardness in 1900, and the discovery revolutionized the engineering field, as it created a standardized scale which could be easily referenced.

In a test for Brinell hardness, the ball used is typically approximately 4/10 of an inch (10 millimeters) in diameter. If the material is extremely hard, the ball will be made from tungsten or carbide, while a plain steel ball is sufficient for softer substances. The amount of pressure also varies depending on the material, but a standard amount of pressure for harder substances is 6,614 pounds (3,000 kilograms). The ball is forced into the material being tested for thirty seconds and then removed so that the indent can be measured. The formula divides the force used by the surface area of the indentation.

When giving the Brinell hardness of a material, it is conventional to list the conditions of the test, and metric measurements are used. The listing starts with the Brinell hardness number, follows with the type of ball used, and then lists the diameter of the ball, the amount of force applied, and the amount of time. For example, pine, an extremely soft wood, would be listed like this: 1.6 HBS 10/100/30. This means that the Brinell hardness of pine is 1.6 when it is impressed with a hardened steel ball which is 4/10 of an inch (10 millimeters) in diameter under a weight of 220 pounds (100 kilograms) for 30 seconds.