Mitutoyo HM-200A Series - Knoop Hardness; What Is Knoop Hardness

4. Hardness test procedure
No. 99MBG127A
4-15
4.2.2 Knoop hardness
4.2.2.1 What is Knoop hardness
Knoop hardness is the value (F/A) that is the test force "F" divided by the projected area "A" of the
indentation that is calculated by the longer diagonal line length "d", where the indentation is made
by a diamond indenter shaped rhombic-based pyramid with edge angles α of 172.5 degrees and
β of 130 degrees and rhombic transverse section.
Fig. 4-3 Reference figure of Knoop hardness Fig. 4-4 Indentation of Knoop hardness test
<Knoop hardness calculation method>
Where
HK: Knoop hardness
c: Indenter constant (constant which calculate A from d)
k: Constant, k=1/g
ｎ
=1/9.806650≒0.102
F: Test force [N]
S: Projected plane area of indentation
d: longer diagonal line length of indentation [mm]
α: First edge angle of indenter (172.5°)
β: Second edge angle of indenter (130°)
g
ｎ
: Standard gravitational acceleration
Where the surface of the specimen must be parallel to the top surface of the stage.
d
22
451.1102.0102.0
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