Hardness Test - Knoop hardness

Principle

 

A diamond indenter, in the form of a rhombic-based pyramid with angles between opposite edges faces respectively equal to 172.5° and 130° at the vertex, is forced into the surface of a test piece followed by measurement of the long diagonal, d, of the indentation remaining in the surface after removal of the test force.


Formulas

 

HK = 0.102 ⋅ F / Ap = 1.451 ⋅ F / d2 ... Knoop hardness
d ... Length of the longer diagonal (about 7 times the short diagonal length)
F ... test force [N]
Ap ... projected area of the indentation

(The area corresponding to a diagonal length is given in tables by most of the manufacturers)

Conditions

 

see standard

History

 

This method, developed by Knoop, Emerson and Peters, was presented for the first time ever in 1939.
Application primarily in micro hardness tests.

Valid standard

 

DIN EN ISO 4545:2006 1 - 4 Metallic materials - Knoop hardness test
DIN ISO 4516:2002 Metallic and other inorganic coatings - Vickers and Knoop micro hardness tests

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