In a tensile test, which measurement most directly indicates a material's ductility?

• A. Tensile strength
• B. Yield strength
• C. Elongation after fracture
• D. Hardness

Answer: (C)

Ductility is how much plastic deformation a material can undergo before it breaks. In a tensile test, the most direct way to quantify that is by how far the specimen stretches before fracture—the elongation after fracture (often given as a percent elongation). A material that can stretch a lot shows high ductility; one that breaks with little to no plastic deformation appears brittle. Tensile strength tells you the maximum load the material can bear, but not how much it deforms; yield strength marks the onset of permanent deformation, not total stretch; hardness relates to surface resistance, not ductility. So elongation after fracture best reflects how ductile the material is.