Which property measures a material's resistance to permanent deformation when a stress is applied?

The property that measures a material's resistance to permanent deformation when stress is applied is plasticity. Plasticity refers to the ability of a material to undergo permanent deformation without breaking when subjected to an external force. When a material is deformed within its elastic limit, it can return to its original shape when the stress is removed. However, once the stress exceeds this limit, the material enters the plastic region where the deformation becomes permanent.

Understanding plasticity is fundamental in material science and engineering because it determines how materials behave under sustained loads and how they can be formed or shaped without fracturing. This characteristic is particularly important when designing components that need to withstand heavy loads or undergo processes like molding, bending, or extruding.

In contrast, strength refers to a material's ability to withstand an applied load without failure, while elasticity measures the extent to which a material can deform elastically (non-permanently) when stress is applied. Ductility, on the other hand, is a specific aspect of plasticity that describes a material's ability to undergo significant plastic deformation before rupture, often manifesting as the ability to be drawn into wires.