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Knoop testing

Testing method for materials in which an indenter whose tip is shaped like an equilateral pyramid creates a depression whose diagonal is translated to Knoop hardness.

Illustration of Knoop testing

The process

As the method typically measures very small values, the surface must be smooth enough before testing can begin. An indenter [1] of diamond, whose tip is designed as an elongated pyramid, is pressed down against the material [2] to be tested. The pressure applied is usually relatively low and maintained for a certain time interval, which creates a depression in the material. Depression diagonals are measured and compared to a table value to obtain a value of the material’s Knoop hardness.

Indenter is similar to that used in the Vickers Test.

Advantages and disadvantages
In comparison with alternative methods
Very small sample is required
Valid for a wide range of forces
Difficult to use the microscope to measure the depression
Time-consuming method for preparation and applying indenter