Yield strength is defined as which of the following?

• A. The amount of energy absorbed by a material before it fractures or permanent deformation
• B. Maximum stress before fracture
• C. Stiffness
• D. Hardness

Answer: (A)

Yield strength is the stress at which a material begins to deform plastically—the point where permanent, non-recoverable deformation starts and the material will not return to its original shape when the load is removed. On a typical stress–strain curve, this marks the end of the purely elastic region and the beginning of plastic deformation, often defined practically by the 0.2% offset method because some materials don’t have a sharp yield point.

The option describing energy absorbed before fracture relates to toughness, not yield strength. The option about maximum stress before fracture corresponds to ultimate tensile strength, not yield. Stiffness refers to the slope of the elastic region (Young’s modulus), and hardness measures resistance to indentation.