Brinell hardness test
The development of the test method
The Swedish engineer Johan August Brinell lived from 1849 to 1925. During his career he researched for alternatives to the resistance test methods that existed until then. His original suggestion was to find a method which was less time-consuming than the tensile test. In 1900, Brinell achieved the breakthrough and he developed the hardness test by means of a ball pressure test. In the same year of his invention he presented this method at the world exhibition in Paris.
Since then this test method has been call the Brinell hardness test method. Today this method is used to determine the hardness of materials with non-uniform microstructures, soft to medium hard metals and even wood.
Performing the test
In the Brinell hardness test a test ball made of sintered carbide is pressed on the material and the impression made by the ball is then evaluated. Originally test balls made of hard metal or hardened steel were used. However, these are no longer allowed since 2006. Since then only balls made of hard metal (sintered carbide) are used. The diameter of the test ball is 10 mm, 5 mm, 2.5 mm, 2 mm or even 1 mm. Which ball is used is determined according to the thickness of the material to be tested. The normal dwell time for the pressure load, depending on the type of material, is 10 to 15 seconds. The dwell time can also be increased up to 30 sec. for very soft materials.
When using the Brinell hardness test it is necessary to ensure that the surface of the material to be tested is smooth, flat and free from impurities. Further, attention must be paid to impact-free and vertical penetration of the test ball. After the pressure load the vertical and horizontal diameter of the impression created are measured. The average of these two values is calculated and this diameter is then used to calculate the Brinell hardness.
F = Test force set at the Brinell hardness test machine (in Newtons)
D = Diameter of the test ball
The formula for calculating Brinell hardness is as follows:
- Due to the relatively little effort required the Brinell hardness test method can be used easily and even under not so good circumstances.
- Relatively high test forces can be applied. Simple but robust equipment is available for this.
- Simple microscopes or magnifying glasses can be used to evaluate the impression made in the test material.
- As already described, the area to be tested must be very clean. This makes a certain amount of preparation necessary. This means that the Brinell test is not a fast method. This method is also not useful for material testing in series.
- The method cannot be used for small or thin materials or even very hard materials, or only conditionally. Due to the visual determination there is a risk of incorrect measurements, however, automatic processing of the images by means of a computer can reduce this risk significantly.