Knoop Hardness Test
Knoop hardness testing method, also known micro hardness test method, tests the hardness of brittle and thin sections. Developed by Fredrick Knoop, the tester uses a pyramid-shaped diamond indenter just like the Vickers hardness test. However, unlike Vickers’ symmetrical shape, the pyramid has an elongated design. The test is based on an optical measurement system. In other words, it measures the long diagonal of the indent optically.
Using Knoop Hardness tester from Innovatest
As the name suggests, it measures micro hardness less than one kgf. It comes in handy for closely spaced indentations, especially at the edge of the sample. A major advantage of this hardness testing method is that indentations are shallow. Also, it provides more resolution from the measurement.
As mentioned, knoop hardness tester takes measurements from small indentations. The measurement is then converted to a hardness number using a chart. For correct measurements, the surface of the materials to be tested should be smooth. Also, the material should be held steady. Here is an important point. Knoop hardness testing is not suitable for tests that show diagonal less below 20 μm.