Which statement defines the 0.2% offset yield strength?

• A. The stress at which permanent plastic deformation of about 0.2% occurs.
• B. The stress at fracture.
• C. The yield point is at the onset of fracture.
• D. The modulus of elasticity at yield.

Answer: (A)

The 0.2% offset yield strength is defined as the stress at which permanent plastic deformation reaches 0.2% of the original gauge length. For many materials, there isn’t a sharp yield point, so we use an offset method: draw a line parallel to the elastic (linear) portion of the stress–strain curve, offset it by 0.2% strain, and where that line intersects the curve gives the yield strength. This value marks the onset of plastic flow, not the point of fracture.

The other statements mix up different concepts: the stress at fracture is the fracture or ultimate tensile strength, not the yield strength; the idea that the yield point is at the onset of fracture is incorrect because yielding occurs well before fracture; and the modulus of elasticity is the slope of the elastic region (Young’s modulus), not a yield stress.