What does the 0.2% offset represent in yield testing?

• A. The onset of plastic deformation
• B. The maximum stress
• C. The fracture point
• D. The elastic limit

Answer: (A)

The 0.2% offset is a practical way to define when plastic (permanent) deformation begins, especially for metals that don’t have a sharp yield point. In a tensile test, the material stretches elastically at first, then plastically. To locate the yield strength, you draw a line parallel to the initial elastic portion of the stress–strain curve but offset by 0.2% strain. The intersection of this line with the curve gives the stress at which 0.2% of permanent deformation has occurred. That stress is the yield strength defined by the 0.2% offset, i.e., the onset of plastic deformation at a small, fixed amount of permanent strain. It isn’t the maximum stress the material can bear, nor the fracture point, nor simply the elastic limit, which is just the end of elastic behavior.