Johann August Brinell (Sweden) presented his new hardness testing method at the world exhibition in Paris in 1900.
In this method, a carbide ball is pressed vertically into the surface of a sample with a certain force. This creates an indentation in the sample surface. The diameter of the indentation d is determined using a measuring microscope and the Brinell hardness is calculated or referred to from the corresponding tables.
1. Indentation of a hard metal ball
2. Measurement of the indentation
CALCULATION OF THE BRINELL HARDNESS
Calculation formula for Brinell hardness:
For the Brinell hardness test, the selection of suitable test parameters is of decisive importance.
The Brinell method becomes inaccurate for very small or very large penetration depths. For this reason, the test load must be selected such that the following conditions are met for the mean indentation diameter:
0,24 * D < d <0,6 * D
In order to meet these conditions, 'Stress level B' was introduced. This depends on the material group to be tested.
The stress level is selected according to the following table:
After the degree of stress has been determined, test load F and ball diameter D can be determined according to the table. In principle, the ball diameter should be as large as possible in order to cover
as large and therefore representative a part of the sample surface as possible.
Hardness values determined with different ball diameters at the same degree of loading can only be compared to a limited extent. Hardness values determined with the same ball diameter but different degrees of loading are not comparable. Therefore, it is essential that all parameters are always specified when specifying a hardness value.
BRINELL HARDNESS TESTING RESULTS
According to DIN EN IS 6506-1 the result of a Brinell hardness test is indicated as follows:
310 HBW 2,5 / 187,2 / 20 ⇒ Hardness value as per Brinell
310 HBW 2,5 / 187,2 / 20 ⇒ Abbreviation for Brinell hardness
310 HBW 2,5 / 187,2 / 20 ⇒ Ball diameter in mm
310 HBW 2,5 / 187,2 / 20 ⇒ Test force [N] = 9.807 * test force specification
310 HBW 2,5 / 187,2 / 20 ⇒
Application time of the test force
(omitted if it is between 1-15 s)
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