Hardness is an important parameter used to measure the resistance of a solid material to physical indentation or penetration. It is a measure of the ability of a material to withstand abrasion, erosion, penetration, scratching and other surface deformations. Hardness can be defined in terms of the ability of a material to resist penetration at the surface, or by the capability to resist compression and wear at the surface. Hardness measurements are used to determine the suitability of a material for many engineering applications such as cutting, grinding and tooling.
Hardness can be measured with different types of instruments. The most common are Rockwell Hardness (RHR), Brinell Hardness (BH) and Vickers Hardness (VH). All these instruments measure the same thing, just using different methodologies. The main differences between them are the sensitivity of the readings and the hardness range that is measured.
The Rockwell Hardness (RHR) test uses a diamond indenter to measure the Hardness of a material. In this test, a load is applied by a diamond indenter to the surface and the hardness is determined by measuring the depth of the indentation left by the indenter. This type of test is suitable for testing hard and brittle materials such as ceramic and steel materials.
The Brinell Hardness (BH) test uses a heavy load (usually 3000kg) applied to a hardened steel ball indenter to measure the indentation of a material. This type of test is especially suitable for materials than can withstand high stresses, such as steel and non-ferrous metals. The Vickers Hardness (VH) test is the most accurate type of the three and is used when high accuracy is needed. In this test, a diamond indenter is used to measure the indentation left in the material by applying a load of 1-2kg. This type of test is suitable for softer materials such as aluminum, copper, brass and plastics.
Wear resistance is another important aspect of measuring hardness. This measure is used to determine the ability of a material to resist abrasion and erosion during service. Wear resistance can be measured in a number of ways, such as measuring the amount of metal removed from a surface under a specified load and pressure. The most common method for measuring wear resistance is the Taber Abrasion Test, which uses a machine to abrade a test specimen with an abrasive wheel. The amount of metal removed is measured and the results are used to calculate the wear resistance of a material.
The Rockwell Hardness (RHR) test is the most commonly used hardness test. Other hardness tests such as Brinell Hardness (BH) and Vickers Hardness (VH) are used for specific applications and when higher accuracy is required. When selecting a material for an application, it is important to consider its hardness as well as its wear resistance. The appropriate hardness and wear resistance will depend on the application and the expected service lifetime of the part.
