Knoop hardness test

A pyramidal diamond point is pressed into the polished surface of the test material with a known (often 100 g) load, for a specified dwell time, and the resulting indentation is measured using a microscope.

The geometry of this indenter is an extended pyramid with the length to width ratio being 7:1 and respective face angles are 172 degrees for the long edge and 130 degrees for the short edge.

The test was developed by Frederick Knoop[2] and colleagues at the National Bureau of Standards (now NIST) of the United States in 1939, and is defined by the ASTM E384 standard.

The main disadvantages are the difficulty of using a microscope to measure the indentation (with an accuracy of 0.5 micrometre), and the time needed to prepare the sample and apply the indenter.

Variables such as load, temperature, and environment, may affect this procedure, which have been examined in detail.