The Brinell test is a test which is used to determine the hardness of materials. Metals are commonly tested in this way, and the Brinell test can also be used on woods and some other materials. This is a form of materials testing, in which the goal is to learn more about a material by subjecting a sample to a set of standardized tests. Brinell test results for a number of common materials, ranging from mahogany to carbon steel, are readily available.
This test was developed in 1900 by Johann Brinell, a Swedish researcher. In the Brinell hardness test, a hard metal ball is pressed into a sample of material with a set amount of weight acting as pressure on the ball. The ball is held in place for 15-30 seconds, and then the weight is released. The ball will have left an indentation behind, and the hardness can be determined by dividing the weight by the area of the indentation.
The size of the ball varies, depending on the material being tested. Testers want to avoid using a ball which is so large that it interferes with the test results. The materials the ball is constructed from also vary, again depending on the material being tested. Chromium steel is one choice, as is tungsten carbide. When test results are published, the size and composition of the ball may be disclosed so that people have a frame of reference.
To understand why balls of different materials and sizes are used, instead of a standardized ball, think about pushing a hand through a cake. With minimal pressure, the hand should quickly travel from the top of the cake all the way to the cake plate. Now, think about using the same amount of pressure, with the same hand, on a marble kitchen counter. The counter would likely be unmoved, and if the pressure was increased, the hand would likely break before an indent appeared in the counter. This example illustrates why different materials are used in a Brinell test, with the ball size and composition being dependent on what is being tested.
Many people use machines which have been specifically designed to administer a Brinell test when they perform this materials test. The machine includes measuring devices which can very accurately determine the diameter of the indent. It is also possible to use a system adapted for the Brinell test, as long as the weight of the pressure can be controlled and a microscope is available to measure the indent.
By Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.