In Brinell hardness testing, what type of indenter is used and how is hardness determined?

• A. A tungsten carbide or hardened steel ball; the diameter of the impression is measured and converted into a Brinell hardness number
• B. A diamond pyramid; the depth of the indentation is measured to compute a hardness number
• C. A sharp conical indenter; the surface roughness determines hardness
• D. A cylindrical pin; the length of indentation determines hardness

Answer: (A)

Brinell hardness testing uses a hard spherical indenter, typically made of tungsten carbide or hardened steel. A known load is applied, and after the test you measure the diameter of the circular impression left on the surface. The hardness number is then calculated from the load and the impression diameter (accounting for the ball diameter) using the Brinell formula. The key idea is that the spherical shape creates a round indent whose size under a given load reflects how resistant the material is to plastic deformation, and measuring that diameter lets you convert deformation into a single hardness value.