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| [[File:Vickers-tester.png|thumb|A Vickers hardness tester]]
| | This is a preview for the new '''MathML rendering mode''' (with SVG fallback), which is availble in production for registered users. |
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| The '''Vickers hardness test''' was developed in 1921 by Robert L. Smith and George E. Sandland at [[Vickers Ltd]] as an alternative to the [[Brinell scale|Brinell]] method to measure the [[hardness]] of materials.<ref>R.L. Smith & G.E. Sandland, "An Accurate Method of Determining the Hardness of Metals, with Particular Reference to Those of a High Degree of Hardness," ''[[Proceedings of the Institution of Mechanical Engineers]]'', Vol. I, 1922, p 623–641.</ref> The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe the questioned material's ability to resist plastic deformation from a standard source. The Vickers test can be used for all [[metal]]s and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the '''Vickers Pyramid Number''' ('''HV''') or '''Diamond Pyramid Hardness''' ('''DPH'''). The hardness number can be converted into units of [[pascal (unit)|pascals]], but should not be confused with a pressure, which also has units of pascals. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not a pressure.
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| == Implementation ==
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| [[File:Vickers-path-2.svg|thumb|Vickers test scheme]]
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| [[File:Vickers anvil diamons.jpg|thumb|The pyramidal [[diamond]] indenter of a Vickers hardness tester.]]
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| [[File:Case hardened steel-vickers hardness test.png|thumb|An indentation left in case-hardened steel after a Vickers hardness test. The difference in length of both diagonals and the illumination gradient, are both classic indications of an out-of-level sample. This is not a good indentation.]]
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| It was decided that the indenter shape should be capable of producing geometrically similar impressions, irrespective of size; the impression should have well-defined points of measurement; and the indenter should have high resistance to self-deformation. A diamond in the form of a square-based pyramid satisfied these conditions. It had been established that the ideal size of a [[Brinell hardness test|Brinell]] impression was 3/8 of the ball diameter. As two tangents to the circle at the ends of a chord 3''d''/8 long intersect at 136°, it was decided to use this as the included angle of the indenter, giving an angle to the horizontal plane of 22° on each side. The angle was varied experimentally and it was found that the hardness value obtained on a homogeneous piece of material remained constant, irrespective of load.<ref>http://www.ukcalibrations.co.uk/vickers_htm.html</ref> Accordingly, loads of various magnitudes are applied to a flat surface, depending on the hardness of the material to be measured. The HV number is then determined by the ratio ''F/A'', where ''F'' is the force applied to the diamond in kilograms-force and ''A'' is the surface area of the resulting indentation in square millimeters. ''A'' can be determined by the formula.
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| | :<math forcemathmode="mathml">E=mc^2</math> |
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| : <math>A = \frac{d^2}{2 \sin(136^\circ/2)},</math> | | <!--'''PNG''' (currently default in production) |
| | :<math forcemathmode="png">E=mc^2</math> |
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| which can be approximated by evaluating the sine term to give
| | '''source''' |
| | :<math forcemathmode="source">E=mc^2</math> --> |
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| : <math>A \approx \frac{d^2}{1.8544},</math> | | <span style="color: red">Follow this [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering link] to change your Math rendering settings.</span> You can also add a [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering-skin Custom CSS] to force the MathML/SVG rendering or select different font families. See [https://www.mediawiki.org/wiki/Extension:Math#CSS_for_the_MathML_with_SVG_fallback_mode these examples]. |
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| where ''d'' is the average length of the diagonal left by the indenter in millimeters. Hence,<ref>ASTM E384-10e2</ref>
| | ==Demos== |
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| : <math>HV = \frac{F}{A} \approx \frac{1.8544 F}{d^2}</math>, | | Here are some [https://commons.wikimedia.org/w/index.php?title=Special:ListFiles/Frederic.wang demos]: |
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| where ''F'' is in [[kilogram-force|kgf]] and ''d'' is in millimeters.
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| The corresponding units of HV are then kilograms-force per square millimeter (kgf/mm²). To calculate Vickers hardness number using SI units one needs to convert the force applied from [[kilogram-force]] to newtons by multiplying by 9.806 65 ([[standard gravity]]) and dividing by a factor of 1000 to get the answer in GPa. To do the calculation directly, the following equation can be used:<ref>ISO 6507-1:2005</ref>
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| | ** From our testing, ChromeVox and JAWS are not able to read the formulas generated by the MathML mode. |
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| : <math>HV = \frac{F}{A} \approx \frac{0.01819 F}{d^2},</math>
| | ==Test pages == |
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| where ''F'' is in N and ''d'' is in millimeters. Here, HV is in GPa and should be roughly between 0-15 GPa.
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| Vickers hardness numbers are reported as '''xxxHVyy''', e.g. '''440HV30''', or '''xxxHVyy/zz''' if duration of force differs from 10 s to 15 s, e.g. 440Hv30/20, where:
| | *[[Inputtypes|Inputtypes (private Wikis only)]] |
| | | *[[Url2Image|Url2Image (private Wikis only)]] |
| * '''440''' is the hardness number,
| | ==Bug reporting== |
| * '''HV''' gives the hardness scale (Vickers),
| | If you find any bugs, please report them at [https://bugzilla.wikimedia.org/enter_bug.cgi?product=MediaWiki%20extensions&component=Math&version=master&short_desc=Math-preview%20rendering%20problem Bugzilla], or write an email to math_bugs (at) ckurs (dot) de . |
| * '''30''' indicates the load used in kgf.
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| * '''20''' indicates the loading time if it differs from 10 s to 15 s | |
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| Vickers values are generally independent of the test force: they will come out the same for 500 gf and 50 kgf, as long as the force is at least 200 gf.<ref>[http://www.instron.us/wa/applications/test_types/hardness/vickers.aspx Vickers Test]. [[Instron]] website.</ref>
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| For thin samples indentation depth can be an issue due to substrate effects. As a general rule of thumb the sample thickness should be kept greater than 2.5 times the indent diameter. Alternatively indent depth can be calculated according to:
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| : <math>h = \frac{d}{2\sqrt{2}\tan{\frac{\theta}{2}}} \approx \frac{d}{7.0006},</math>
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| {| class="wikitable" border="1"
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| |+ Examples of HV values for various materials<ref>Smithells Metals Reference Book, 8th Edition, ch. 22</ref>
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| ! Material !! Value
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| | 316L stainless steel || 140HV30
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| | 347L [[stainless steel]] || 180HV30
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| | [[Carbon steel]] || 55–120HV5
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| | [[Iron]] || 30–80HV5
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| | [[Martensite]] || 1000HV
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| | [[Diamond]] || 10000HV
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| |}
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| ==Precautions==
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| When doing the hardness tests the minimum distance between indentations and the distance from the indentation to the edge of the specimen must be taken into account to avoid interaction between the work-hardened regions and effects of the edge. This minimum distances are different for ISO 6507-1 and ASTM E384 standards.
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| {| class="wikitable" border="1"
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| ! Standard !! Distance between indentations !! Distance from the center of the indentation to the edge of the specimen
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| | ISO 6507-1 || > 3·d for steel and copper alloys and > 6·d for light metals || 2.5·d for steel and copper alloys and > 3·d for light metals
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| | ASTM E384 || 2.5·d || 2.5·d
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| |}
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| ==Estimating tensile strength== | |
| If HV is expressed in <math>\mbox{kg/mm}^2</math> the [[tensile strength]] (in MPa) of the material can be approximated as: | |
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| <math>{\sigma_u} \approx {\H_V}*c \approx {\H_V}*{3.33}</math>
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| where c is a constant determined by geometrical factors usually ranging between 2 and 4. <ref>{{cite web|title=Hardness|url=http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=150&pageid=2144416429}}</ref>
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| ==Application==
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| The [[Vertical stabilizer|fin]] attachment pins and sleeves in the [[Convair CV-240 family|Convair 580]] airliner were specified by the aircraft manufacturer to be hardened to a Vickers Hardness specification of 390HV5, the '5' meaning five [[Kilogram-force|kiloponds]]. However on the aircraft flying [[Partnair Flight 394]] the pins were later found to have been replaced with sub-standard parts, leading to rapid wear and finally loss of the aircraft. On examination, accident investigators found that the sub-standard pins had a hardness value of only some 200-230HV5.<ref>http://www.aibn.no/aviation/reports/1993-02-eng</ref>
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| == See also ==
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| {{multicol}}
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| * [[Indentation hardness]]
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| * [[Leeb Rebound Hardness Test]]
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| * [[Hardness comparison]]
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| * [[Knoop hardness test]]
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| {{multicol-break}}
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| * [[Meyer hardness test]]
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| * [[Rockwell scale]]
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| * [[Ceramography#Microindention hardness and toughness|Vickers toughness test of ceramics]]
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| {{multicol-end}}
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| == References ==
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| ===Notes===
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| {{reflist}}
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| Note 7 is a link to a source that gives conversion formula as Vickers Hardness (HV) ~ 0.3 × yield stress (in MPa) which is wrong as it should be Vickers Hardness (HV) ~ 0.3 × ultimate stress (in MPa)
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| ===Bibliography===
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| * {{cite book
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| | author = Meyers and Chawla
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| | year = 1999
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| | chapter = Section 3.8
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| | title = Mechanical Behavior of Materials
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| | publisher = Prentice Hall, Inc
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| }}
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| ==Further reading==
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| *[[ASTM]] E92: Standard method for Vickers hardness of metallic materials (Withdrawn and replaced by E384-10e2)
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| *ASTM E384: Standard Test Method for Knoop and Vickers Hardness of Materials
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| *[[International Organization for Standardization|ISO]] 6507-1: Metallic materials - Vickers hardness test - Part 1: Test method
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| *ISO 6507-2: Metallic materials - Vickers hardness test - Part 2: Verification and calibration of testing machines
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| *ISO 6507-3: Metallic materials - Vickers hardness test - Part 3: Calibration of reference blocks
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| *ISO 6507-4: Metallic materials - Vickers hardness test - Part 4: Tables of hardness values
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| ==External links==
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| * [http://www.youtube.com/watch?v=7Z90OZ7C2jI Video on the Vickers hardness test]
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| * [http://www.gordonengland.co.uk/hardness/vickers.htm Vickers hardness test]
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| * [http://www.struers.com/default.asp?top_id=5&main_id=25&doc_id=344&target=_self&collapse=1 Conversion table] - Vickers, Brinell, and Rockwell scales
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| [[Category:Hardness tests]]
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| [[de:Härte#Härteprüfung nach Vickers (HV)]]
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