Steel Ductility Measurements

Ductility is essential for the fabrication and adequate performance of cold-formed steel structures. For defining safe minimum values of ductility, it is first necessary to develop reliable ductility measurements. It is shown that the usual percent elongation in a 2-in. gage length of a standard rectangular coupon is not a consistent measure of ductility and that reduction in area is difficult to measure for sheet and strip steel specimens. Distinction is made between uniform elongation observed in a specimen over a length outside the fracture zone, and local elongation measured over a short length across the fracture. The separate and complementary roles of uniform and local ductility are presented. Several measures for these two distinct properties are described. Two methods for separately measuring uniform and local ductility by minor modifications of the standard ASTM tension test are proposed.