Within the hardness tests of materials that are usually applied in the industrial sector, the Brinell test is one of the most famous tests, especially due to its age and low cost. In this post we tell you what exactly it consists of, how it is done and when it is used.
What is a Brinell trial?
Brinell hardness tests are tests carried out on certain materials to find out their resistance to penetration by other compounds. This method was invented in 1900 by the Swedish engineer Johan August Brinell, becoming the first scientific procedure for measuring penetration hardness.
How is a Brinell hardness test performed?
In a Brinell test, the estimation of hardness takes place through the process known as indentation. It consists of applying an object (indenter or penetrator) with a certain load on the surface of the material to be studied. Subsequently, the depth of the footprint generated is measured with a microscopic magnifying glass. All this is done with a calibrated machine called a durometer.
The charge, the time of action and the diameter of the indenter vary depending on the thickness of the sample and the hardness of the substance to be analyzed. For softer materials, the penetrating object is a tempered steel ball of varying diameter, typically between 1 and 10 mm. However, for harder materials such as metals, a tungsten carbide (tungsten) ball is used.
The hardness of the Brinell scale is expressed in HB and is calculated by dividing the force (P) of the load used by the surface (S) of the mark obtained:
HB = P / S
What standard regulates Brinell tests?
Currently, the international standard that regulates the planning and implementation of this type of tests for metals is the ISO 6506 standard, commonly known as the Brinell standard and composed of four parts:
- ISO 6506-1: Test method.
- ISO 6506-2: Verification and calibration of testing machines.
- ISO 6506-3: Calibration of reference blocks.
- ISO 6506-4: Tables of hardness values.
In America, these tests are regulated by ASTM E10-08. Although in both cases the indentation time usually oscillates between 10 and 15 seconds, in the Brinell ISO standard, the thickness of the sample must equal, at least, eight times the penetration depth, while in the Brinell standard americana, the thickness increases to a minimum of 10 times this distance.
When are Brinell hardness tests used?
The main drawback of Brinell tests is that they are only valid for relatively soft materials of sufficient thickness. Also, the result is very sensitive to irregularities on the surface of the sample, so it must be clean, flat and polished. Neither can it be spherical or cylindrical.
In contrast, the most prominent advantage of Brinell hardness testing is its low cost compared to other similar techniques. In addition, provided the surface is properly prepared, they can be used on large granular and heterogeneous samples of a wide range of materials, including different varieties of iron, steel, aluminum, bronze, copper, brass, tin, and lead, as well as other soft metals, light alloys, and even wood.
On the other hand, it should be noted that the hardness result on the Brinell scale can be directly related to the static resistance of materials. Therefore, although the Brinell test is not the most advanced method available to measure the hardness of materials, it is a very useful procedure to study the nature of certain compounds.