The Vickers hardness test, developed in 1925, uses mechanical force to determine the hardness of materials. A diamond tip is used to create an indentation, and the force applied is measured using a digital gauge. The hardness number is obtained by dividing the force by the diagonal mean squared. Vickers hardness testing devices can be handheld or standalone machines.
In 1925, two British men developed the Vickers hardness test (HV), which uses mechanical force to determine the hardness of metals or other materials. The force generally leaves a visible impression, which engineers measure to obtain the Vickers pyramid number, a number from zero to 900. The higher the number obtained on a Vickers hardness test, the harder the material.
The first part of the Vickers hardness test is to use a diamond tip which leaves an imprint on the material to be tested. The tip of the tip has a microscopic pyramid shape with a square base. Some people refer to the test as a diamond pyramid hardness test, or DPH, due to the shape of the tip. In larger test fixtures, the bit is placed into a drill press-like tool that is lowered onto the object to be tested. The tip of the drill makes contact with the material and the technicians apply a controlled force for 10-15 seconds.
Testers use a digital gauge to indicate the amount of force applied. After removing the tip, the test object has an indentation in the shape of an inverted pyramid. The press applies 2.2 to 220.5 pounds (1 to 120 kilograms) of sustained pressure, and industries use this force to test the hardness of everything from gems to metals. The Vickers microhardness test typically uses 0.022 to 2.2 pounds (10 to 1,000 grams) of sustained force. Industries use the microtest to determine the hardness of thinner materials and specialty coatings.
Using a specially designed microscope, technicians measure the length of both diagonals of the footprint and average the numbers. They determine the hardness number using conversion tables or with Vickers hardness testing software. The number is obtained by dividing the amount of force by the diagonal mean squared and is written in a specific format, such as 500HV/15. The number 500 indicates the level of hardness and the 15 indicates that force was applied for 15 seconds.
Vickers hardness testing devices can be handheld devices or standalone computerized machines. Portable and portable testers have a force application device connected to a small digital readout monitor. Benchtop versions look like large microscopes with the diamond tip located on the rotating lens. These tools apply the desired amount of force, allowing technicians to measure the footprint by placing microscopic lines on opposite diagonals. The internal software of most modern Vickers hardness testing devices performs the hardness calculations automatically.
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