What term describes materials that resist deformation under load?

• A. Toughness
• B. Ductility
• C. Hardness
• D. Stiffness

Answer: (D)

Resisting deformation under load is what stiffness describes. It tells you how much a material resists changing shape when a force is applied. A stiffer material deflects only a little under the same load, while a less stiff one bends or stretches more. This behavior is tied to stiffness being related to the modulus of elasticity (Young’s modulus): a larger modulus means the material is stiffer, since stress (force per area) causes only a small amount of strain (deformation per original length).

For example, steel is quite stiff and barely deforms under everyday loads, whereas rubber deforms dramatically.

Toughness is about how much energy a material can absorb before it fractures, which involves both deforming and absorbing energy. Ductility is about how much permanent plastic deformation a material can undergo before breaking. Hardness is about resisting surface indentation, not overall deformation under a loading condition.