How is ductility defined in relation to materials?

Ductility is defined as the ability of a material to deform plastically before it fractures. This property is critical in understanding how materials behave under stress. When a ductile material is subjected to tensile stress, it can undergo significant deformation—such as stretching or elongating—without immediately breaking. This behavior is particularly important in engineering and manufacturing, as it allows for safe deformation and shaping of materials during processes like forming, welding, and machining.

In contrast, the other options represent different material properties. Conductivity relates to how well a material can conduct electricity, which is unrelated to ductility. Resistance to deformation is more aligned with stiffness or elasticity, not ductility, which specifically concerns plastic deformation. The ability to return to the original shape after stress describes elastic behavior, not ductility. Thus, the definition that encapsulates ductility accurately is its capacity for plastic deformation prior to failure.