Vickersmenetelmä

Vickersmenetelmä, also known as Vickers hardness test, is a method for determining the hardness of materials. Developed by Robert L. Smith and George Sandland of the Vickers Limited company in the 1920s, it is a widely used technique for material science and engineering. The test involves impressing a square-based diamond pyramid indenter into the surface of the material being tested. The indenter has an angle of 136 degrees between opposite faces. The load applied is typically between 1 kgf and 120 kgf, and it is maintained for a specific period, usually 10 to 15 seconds.

After the load is removed, the length of the two diagonals of the indentation left on the surface is measured under a microscope. The Vickers hardness number (HV) is then calculated using the applied load divided by the surface area of the indentation. The formula for HV is approximately 2Lcos(α)/d², where L is the load in kilograms-force and d is the average length of the diagonals in millimeters, and α is half the angle of the indenter (68 degrees).

The Vickers hardness test is advantageous because it can be used on a wide range of materials, from very soft metals to very hard ceramics. It is also insensitive to the applied load, meaning that different loads will produce the same hardness number for a given material, provided the indenter is not too deeply embedded. This makes it a reliable method for comparing the hardness of different materials. The test can be performed at various temperatures, and specialized equipment exists for testing at elevated temperatures.