The ability of a material to resist indention by measuring its depth is what is referred to as hardness. Knoop hardness test is a mechanical testing used on thin sheets especially on materials that are brittle. This test measures material characteristics and functionality.
Procedure of Testing
Optically, the size of the indentation left by the indenter is measured. A test material of a known load is pressed for a given duration (dwell-time), and the indention measurements are taken using a microscope. A pyramid-like diamond point is pressed to create a small indentation into the polished surface of the test material. The lower the indent, the harder the material under test.
Reading the Test
Though not commonly practiced, the dwell time of the test load is at least 10 to 15 seconds. The Knoop hardness testing comprises of, the numeric hardness value (Hardness according to Knoop) denoted as “HK,” and applied test load in “kgf.”
The shallow indentation depth makes the method suitable for testing very thin layers such as aluminum foil. The long and narrow (elongated) test indent is best fit for small, and longish test specimens as well as testing very hard and brittle materials such as glass and ceramics.
To sum up, the Knoop longitudinal diagonal is around three times longer than other tests diagonal. Therefore, it provides higher measurement precision, especially in conjunction with very low test loads. The test is non-destructive, and there is only minor damage to the specimen surface.