<P> The Knoop hardness test / kəˈnuːp / is a microhardness test -- a test for mechanical hardness used particularly for very brittle materials or thin sheets , where only a small indentation may be made for testing purposes . A pyramidal diamond point is pressed into the polished surface of the test material with a known ( often 100g ) 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 depth of the indentation can be approximated as 1 / 30 of the long dimension . The Knoop hardness HK or KHN is then given by the formula : </P>
knoop hardness test is used to measure the hardness of
very brittle materials or thin sheets