Hardness Tester

Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation. In general, different materials differ in their Hardness,
Macroscopic hardness is generally characterized by strong intermolecular bonds.

Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.

There are 3 main types of Hardness measurements:

  1. Scratch Hardness – It is the measure of how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object.The principle is that an object made of a harder material will scratch an object made of a softer material. When testing coatings, scratch hardness refers to the force necessary to cut through the film to the substrate. The most common test is Mohs scale, which is used in mineralogy. One tool to make this measurement is the sclerometer.
  2. Indentation Hardness – This Hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object. Tests for indentation hardness are primarily used in engineering and metallurgy fields. The tests work on the basic premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter. Common indentation hardness scales are RockwellVickersShore, and Brinell, amongst others
  3. Rebound Hardness – This hardness, also known as dynamic hardness, measures the height of the “bounce” of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity. The device used to take this measurement is known as a scleroscope.

Rockwell Hardness testing:

Rockwell testing is the most used method by virtue of the quick results generated and is typically used on metals and alloys.The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test measuring the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a minor load.

Operating: The determination of the Rockwell hardness of a material involves the application of a minor load followed by a major load. The minor load establishes the zero position. The major load is applied, then removed while still maintaining the minor load. The depth of penetration from the zero datum is measured from a dial, on which a harder material gives a lower measure. That is, the penetration depth and hardness are inversely proportional. The chief advantage of Rockwell hardness is its ability to display hardness values directly, thus obviating tedious calculations involved in other hardness measurement techniques.The equation for Rockwell Hardness is {\displaystyle HR=N-{\frac {d}{s}}}HR = N-d/s , where d is the depth (from the zero load point), and N and s are scale factors that depend on the scale of the test being used.

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