27 February 2021

Knoop Hardness Testing

It is a diamond indenter with long and short Knoop diagonals used to measure material hardness. Knoop hardness testing is the best in determining material hardness on smaller objects. It lists materials with 200gf to 500gf as the perfect sample for hardness testing. Although its readings are among the best, such capacity limits its utility range.

How to Test Using Knoop Tester

Materials used to test should be light so as to get the right hardness. First, polish the surface of the material to remove extra weight. The diamond indenter, which is approximately 100g, presses on the material for a specified period. The resulting indentation is then subjected to a microscope test to ascertain its depth. It is from this depth that the material hardness is calculated.

Luckily, the process only needs a small sample of the material. However, the environment, temperature and load can affect the reading if not well regulated.


Characteristics of Knoop Hardness Tester

  • Indention takes a diamond shape where the difference between the long and short diagonals determines the material hardness.
  • It is suitable for smaller and less bulky materials – the tester can accurately give results to materials between 200gf to 500gf. Any material above 1000gf can still produce results, but the variation will be more significant.
  • Knoop hardness testing is influenced by removing damages caused during preparation. However, when the induced testing force reduces, variations continue to widen.