Which property of a material allows it to be permanently stretched without fracture?

Ductility is the property of a material that allows it to be permanently stretched or deformed without breaking. This characteristic is particularly important in materials that are subjected to tensile forces, as ductile materials can undergo significant deformation before reaching their fracture point.

Ductility is typically associated with metals and some polymers, which can be elongated into wires or thin sheets during manufacturing processes like drawing or extrusion. In applications where materials need to be formed into specific shapes or need to absorb energy from impacts without fracturing, ductility is highly desirable.

Plasticity refers to a material's ability to undergo permanent deformation under applied stress but does not exclusively imply the ability to stretch extensively. Malleability, while closely related, specifically refers to a material's ability to deform under compression, making it more applicable to sheet metal forming rather than stretching. Toughness is the ability of a material to absorb energy and plastically deform without breaking, which is a different aspect of material behavior, focusing on the energy absorption capacity rather than permanent deformation through stretching.

In summary, ductility directly addresses the capability to be permanently elongated, making it the correct choice for understanding how materials can be stretched without fracturing.