# Knoop hardness

Knoop hardness

a measure of the hardness of a material, calculated by measuring the indentation produced by a diamond tip that is pressed onto the surface of a sample. The test was devised in 1939 by F. Knoop and colleagues at the National Bureau of Standards in the United States. By using lower indentation pressures than the Vickers hardness test, which had been designed for measuring metals, the Knoop test allowed the hardness testing of brittle materials such as glass and ceramics.

The diamond indenter employed in the Knoop test is in the shape of an elongated four-sided pyramid, with the angle between two of the opposite faces being approximately 170° and the angle between the other two being 130°. Pressed into the material under loads that are often less than one kilogram-force, the indenter leaves a four-sided impression about 0.01 to 0.1 mm in size. The length of the impression is approximately seven times the width, and the depth is 1/30 the length. Given such dimensions, the area of the impression under load can be calculated after measuring only the length of the longest side with the aid of a calibrated microscope. The final Knoop hardness (HK) is derived from the following formula:

HK = 14.229(F/D2),

with F being the applied load (measured in kilograms-force) and D2 the area of the indentation (measured in square millimetres). Knoop hardness numbers are often cited in conjunction with specific load values.

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Universalium. 2010.

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• Knoop hardness number (HK) — Knoop hardness number (HK). См. Число твердости по Кнупу. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

• Knoop hardness test — Knoop hardness test. См. Определения твердости по Кнупу. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

• Knoop hardness test — The Knoop hardness test 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 …   Wikipedia

• Knoop hardness — (HK or KHN)    a measure of the hardness of a metal introduced by Knoop in 1939. The Knoop test is similar to the Vickers test in that a diamond penetrator is used to indent the sample being tested, but it uses a rhombohedral diamond rather than… …   Dictionary of units of measurement

• Knoop hardness — /nup ˈhadnəs/ (say noohp hahdnuhs) noun microhardness of metal measured by resistance to indentation by a pyramidal diamond indentor. {named after Frederick Knoop, 1878–1943, US instrument maker who devised this means of measuring metal hardness} …

• knoop hardness — ˈnüp noun Usage: usually capitalized K Etymology: after F. Knoop, 20th century American chemist : the relative hardness of a material (as a metal) that is determined by the depth to which the bluntly pointed diamond pyramid of a special… …   Useful english dictionary

• Knoop hardness number — See under number. * * * a number indicative of the degree of relative hardness of a material, calculated from the load employed and the length of the long axis of the impression made by the rhomboidal pyramid of a diamond pressed into the surface …   Medical dictionary

• Knoop hardness test — a micro hardness test in which an elongated pyramidical diamond is pressed into the surface …   Mechanics glossary

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