A diamond indenter, in the form of a right pyramid with a square base and with a specified angle between opposite faces at the vertex, is forced into the surface of a test piece followed by measurement of the diagonal length of the indentation left in the surface after removal of the test force, F. The vickers hardness is proportional to the quotient obtained by dividing the test force by the sloping area of the indentation, which is assumed to be a right pyramid with a square base, and having at the vertex the same angle as the indenter.

Symbols and designation thereof:

Designation of Vickers Hardness

Test Forces

Position of indentation

Measures the lengths of the two diagonals. The arithmeticals mean of the two readings shall be taken for the calculation of the Vickers hardness. For flat surfaces, the difference between the lengths of two indentation diagonals should not be greater than 5%. If the difference is greater, this shall be stated in the test report. Magnifications should be provided so that the diagonal can be enlarged to greater than 25% but less than 75% of the field view.
 

Maximum permissible percentage error of the testing machine

Cylindrical surface

Table B.3 to B.6 give the correction factors when tests are made on cylindrical surfaces. The correction factors are tabulated in terms of the ratio of the mean diagonal d of the indentation to the diameter D of the cylinder.

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