In the Rockwell hardness test, what is used to apply force to the surface of the material?

In the Rockwell hardness test, a diamond cone or sphere is utilized to apply force to the surface of the material being tested. This specific indenter is essential because it allows for the precise measurement of hardness based on the depth of penetration under a specified load. The diamond material ensures durability and maintains sharpness, providing accurate and repeatable results across various types of materials.

The hardness test works by first applying a minor load, which creates an initial indentation. Following this, a major load is applied to expand the indentation, and once the major load is removed, the depth of penetration left by the indenter under the minor load is measured. This depth directly correlates to the material's hardness value.

Factors such as the shape and material of the indenter play a critical role in the accuracy of the measurements in the Rockwell hardness test, reinforcing why a diamond cone or sphere is chosen for its hardness and ability to produce reliable results.