How to Measure Hardness
HARDNESS is a measure of how mechanically resistant a material (sample) is to the mechanical penetration of an indenter (a harder body) or as the resistance of a specific material to localised plastic deformation. Hardness tests are extremely important and frequently applied in materials science and are a standard measurement for mechanical materials testing in such materials as metals and stone such as quartz, granite and concrete. The measurement of hardness is usually quick and simple to perform and indicates a major material property and how materials will behave under certain loads. It is therefore used in quality control/assurance to assess incoming goods and outgoing goods inspection but is also an essential tool in research when developing and improving materials and technologies. Measuring hardness is crucial to assess whether a material is suitable for a particular function or the manufacture of a specific technical part of a product.
Whilst hardness measurement is common and fully established in certain material fields it is a property that is referred to and measured in many other industries such as pharmaceuticals, cosmetics and food. Hardness is not a fundamental property of a material – for example, it can be changed by heat. There are hardness ranges, however, within which certain materials lie and the hardness value measured can depend on, for example, how the material is measured, the force applied to the material, the geometry of the indenter and the time that it is in the material. Hardness of metals, for example, is related and dependent on other properties such as stiffness, strength, strain, ductility and yield strength.
When measuring hardness a force is usually applied whereby either the penetration depth or the size of the indentation caused by the indenter is measured. Alternatively, using a Texture Analyser the force to go to a set distance in the material would also indicate and be a suitable way to assess hardness. Brinell, Vickers and Shore hardness are all methods that measure material hardness and can be easily determined using a Texture Analyser.
Typical Probe/Fixture used for Measurement
Whilst indentation is the traditional way of measuring hardness, the term hardness can be so broadly used that there are other options of empirically or imitatively measured the property of hardness according to a customer’s perception of the property, such as bending, compression or tension. In certain cases, the product or sample may have a limitation of presenting to the Texture Analyser for testing according to a standard method. A non-standard compromising solution can usually be found to optimise the testing of the required product property.
Typical Probe/Fixture used for Measurement of Hardness:
Compression Probes >
Penetration Probes >
Multiple Compression/Penetration Probes >
Knife Blades of all varieties >
Typical Hardness properties that can be obtained from a texture analyser graph:
Hardness, Work of penetration, Work of compression, Ductility, Yield Strength, Stiffness, Strength, Strain
Typical Texture Analyser Hardness graph
Shore A Hardness of 3 polyurethane sheet types
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