Which statement best describes toughness?

• A. Absorbs energy before fracture (area under the entire stress-strain curve)
• B. Elastic modulus
• C. Hardness
• D. Ductility

Answer: (A)

Toughness is about how much energy a material can absorb before it fails, which means it depends on both strength and ductility. In a tensile test, the stress-strain curve shows how the material deforms and how much stress it can sustain as it strains up to fracture. The total area under that curve up to the point of fracture represents the energy per unit volume the material can absorb before breaking. That is why toughness is described as the area under the entire stress-strain curve.

This concept clarifies why toughness isn’t just about the elastic modulus (stiffness), which measures resistance to elastic deformation, or about hardness, which reflects resistance to indentation, or even about ductility alone, which is how far the material can plastically deform. Toughness requires both sufficient strength and the ability to deform plastically to blunt cracks and absorb energy, so the area under the full stress-strain curve best captures it.