Which test measures the material's resistance to permanent indentation?

• A. Tensile test
• B. Fatigue test
• C. Hardness test
• D. Impact test

Answer: (C)

Hardness is about how well a material resists localized plastic deformation when an indenter is pressed into its surface. In a hardness test, a defined indenter and load create an indentation that remains permanent; the smaller the indentation for a given load, the harder the material. Common hardness tests include Brinell, Rockwell, and Vickers, each using a different indenter geometry but all measuring resistance to indentation. The other tests measure different properties: a tensile test looks at how a material stretches and yields; a fatigue test examines how many cycles of loading it can withstand before cracking; an impact test assesses toughness by absorbing energy in a high-rate impact. Therefore, the test described is the hardness test.