What term describes the condition of a material when it breaks down and deforms permanently due to increased stress above the elastic limit?

The term that best describes the condition of a material when it breaks down and deforms permanently due to increased stress above the elastic limit is plasticity. Plasticity refers to the capability of a material to undergo significant and permanent deformation when subjected to stress that exceeds its elastic limit. In this state, the material will not return to its original shape once the stress is removed; instead, it retains the new shape acquired during deformation.

Elasticity, in contrast, describes a material's ability to return to its original shape after the stress is removed, operating within its elastic limit. Hardness indicates a material's resistance to deformation or scratching, often measured by its ability to withstand localized plastic deformation. Stiffness refers to the rigidity of a material when subjected to stress, related to how much it deforms elastically under a given load. Therefore, plasticity is the appropriate term for permanent deformation beyond the elastic limit.