Which hardness test is based on measuring the depth of indentation?

• A. Brinell
• B. Vickers
• C. Rockwell
• D. Barcol

Answer: (C)

The Rockwell hardness test is based on measuring the depth of indentation. In this method, a hard steel or carbide ball, or a diamond cone (known as a brale), is pressed into the material under a specific load. After this initial load is applied for a specified duration, an additional minor load is applied, and the depth of the indentation left on the material is measured. The depth of this indentation directly correlates to the hardness of the material: the deeper the indentation, the softer the material and vice versa. This relationship allows for a straightforward and quick determination of hardness values.

In contrast, while the Brinell hardness test also involves indentation, it measures the diameter of the indentation created by a hardened steel ball under a specified load, rather than depth. The Vickers test measures the diagonal length of a diamond-shaped indentation, and the Barcol test is generally used for softer materials and measures hardness based on the depth of penetration of a sharp indenter rather than the residual geometric parameters of the indentation. Thus, the method of evaluating indentation depth makes Rockwell the correct choice here.