ductility

Ductility is another important mechanical property. It is a measure of the degree of plastic deformation that has been sustained at fracture. A material that experiences very little or no plastic deformation upon fracture is termed brittle. The tensile stress–strain behaviors for both ductile and brittle materials are schematically illustrated in Figure (1)
Ductility may be expressed quantitatively as either percent elongation
Or percent reduction in area. The percent elongation %EL is the percentage of plastic strain at fracture, where lf is the fracture length10 and l0 is the original gauge length as above. Inasmuch as a significant proportion of the plastic deformation at fracture is confined to the neck region, the magnitude of %EL will depend on specimen gauge length.
%RA is defined as
where A0 is the original cross-sectional area and Af is the cross-sectional area at the point of fracture. Furthermore, for a given material the magnitudes of %EL and %RA will, in general, be different. Most metals possess at least a moderate degree of ductility at room temperature; however, some become brittle as the temperature is lowered.