Hardness is defined as a measure of the resistance of a material to permanent deformation.

• A. A measure of the resistance of a material to permanent deformation.
• B. The energy absorbed before fracture.
• C. The stress at which 0.2% strain occurs.
• D. The ratio of tensile strength to density.

Answer: (A)

Hardness tests quantify the resistance of a material to permanent deformation manifested as an indentation under an applied load. This focuses on plastic deformation at the surface, which is why hardness reflects how easily a material can be permanently deformed at contact. It’s not about the energy a material can absorb before fracture (that’s toughness), nor about the yield point where plastic deformation begins under tensile loading (0.2% offset yield), nor about a strength-to-weight metric. Hardness often correlates with strength, but its defining idea is resistance to permanent, localized deformation, making the statement the best description.