|
|
| Line 1: |
Line 1: |
| The '''Knoop hardness test''' {{IPAc-en|k|ə|ˈ|n|uː|p}} 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 [[pyramid]]al [[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.<ref>[http://www.gordonengland.co.uk/hardness/microhardness.htm "Microhardness Test", Surface Engineering Forum]</ref> The Knoop hardness ''HK'' or ''KHN'' is then given by the formula:
| | I am Desiree and was born on 26 September 1985. My hobbies are Chainmail making and Geocaching.<br><br>Feel free to visit my blog :: [http://pp8.superhost.pl/serwis/modules.php?name=Your_Account&op=userinfo&username=MB32 FIFA 15 coin hack] |
| | |
| :<math>HK={{\textrm{load}(\mbox{kgf})} \over {\textrm{impression\ area} (\mbox{mm}^2)}}={P \over {C_pL^2}}</math>
| |
| | |
| where:
| |
| :''L'' = length of indentation along its long axis
| |
| :''C''<sub>p</sub> = correction factor related to the shape of the indenter, ideally 0.070279
| |
| :''P'' = load | |
| | |
| HK values are typically in the range from 100 to 1000, when specified in the conventional units of g<sub>f</sub>·mm<sup>−2</sup>. The SI unit, [[pascal (unit)|pascal]]s, are sometimes used instead: 1 kg<sub>f</sub>·mm<sup>−2</sup> = 9.80665 MPa.
| |
| | |
| The test was developed by Frederick Knoop<ref>{{cite journal|author=F. Knoop, C.G. Peters and W.B. Emerson|title=A Sensitive Pyramidal-Diamond Tool for Indentation Measurements|journal=Journal of Research of the National Bureau of Standards|volume=23|issue=1|year=1939| pages=39–61 (Research Paper RP1220)|url=http://archive.org/details/jresv23n1p39|doi=10.6028/jres.023.022}}</ref> and colleagues at the National Bureau of Standards (now [[NIST]]) of the [[USA]] in 1939, and is defined by the [[ASTM]] E384 standard.
| |
| | |
| The advantages of the test are that only a very small sample of material is required, and that it is valid for a wide range of test forces. 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 effect this procedure, which have been examined in detail.<ref>{{cite journal|last=Czemuska|first=J. T.|journal=Proc. Br. Ceram. Soc.|year=1984|volume=34|pages=145-156}}</ref>
| |
| | |
| [[File:Knoop-and Mohs- scale.svg|thumb|250px|Comparison between the Mohs and the Knoop scales.]]
| |
| {| class="wikitable"
| |
| |+ Sample values
| |
| !Material !! HK
| |
| |-
| |
| |[[Dentin]] || 68
| |
| |-
| |
| |[[Gold]] foil || 69
| |
| |-
| |
| |[[Tooth enamel]] || 343
| |
| |-
| |
| |[[Quartz]] || 820
| |
| |-
| |
| |[[Silicon carbide]] || 2480
| |
| |-
| |
| |[[Diamond]] || 7000
| |
| |}
| |
| | |
| == See also ==
| |
| {{Div col}}
| |
| * [[Vickers hardness test]]
| |
| * [[Ceramography#Microindention hardness and toughness|Knoop hardness of ceramics]]
| |
| * [[Leeb Rebound Hardness Test]]
| |
| * [[Meyer hardness test]]
| |
| {{Div col end}}
| |
| | |
| == References ==
| |
| {{reflist}}
| |
| | |
| == External links ==
| |
| * [http://www.efunda.com/units/hardness/convert_hardness.cfm?cat=Steel&HD=HK efunda]
| |
| * [http://web.archive.org/web/20080113233200/http://www.lib.umich.edu/dentlib/Dental_tables/Knoophard.html Dental hardness tables]
| |
| | |
| [[Category:Hardness tests]]
| |
| | |
| [[de:Härte#Härteprüfung nach Knoop]]
| |
I am Desiree and was born on 26 September 1985. My hobbies are Chainmail making and Geocaching.
Feel free to visit my blog :: FIFA 15 coin hack