The Vickers hardness test is one of the static mechanical tests that can be used to measure the hardness of materials.
In specific, the force used for the indentation of the material is determined, followed by the optical measurement of the size of the indentation.
This means that it is the optical acquisition of the indentation size generated by the indenter, together with the value of the load force, that determines the hardness value.
The range of hardnesses applicable in this case is very wide. For the purpose of convenience, we speak of two “families”, separate from each other:
However, there are variables that must be considered when choosing which load forces to use, including:
We recommend identifying the best procedure based on specific personal needs with the help of the ISO 6507-1, ASTM E92 and ASTM E384 standards (the latter in the case of Vickers micro hardness).
Imagine a bench top hardness tester equipped with an indenter in the shape of a straight pyramid (with a vertex angle of 136°), with a square diamond base. The hardness test starts when the indenter comes into contact with the surface of the sample to be measured.
After a localized pressure of a few seconds (usually between 10 and 15 seconds), the force is removed.
At this point, a special algorithm processes the images from the optical system on the basis of the Vickers hardness principle and calculates the average of the diagonals of the indentation generated by the indenter, therefore allowing to calculate the hardness value (for which the unit of measure is indicated with “HV”).
To be more precise, this value is determined by the ratio between the applied force (expressed in Newton or kgf) and the lateral surface of the indentation after the force has been removed. Here’s the formula:
This formula is developed further to arrive at the final calculation expressed below:
In practice, however, to quickly calculate the hardness value it is sufficient to refer to the tables attached to the reference standards, without having to materially apply the formula just described.