On a stress-strain curve, which event marks the end of elastic behavior?

• A. End of elastic behavior with onset of plastic deformation.
• B. Maximum elastic strain.
• C. Ultimate tensile strength.
• D. Zero strain.

Answer: (A)

The main idea is that elastic behavior is the reversible portion of deformation, where stress and strain are proportional and the material springs back when the load is removed. The end of this elastic region occurs at the yield point, where plastic deformation begins. At this point, dislocations start to move and permanent, non-reversible changes accumulate, so the material no longer returns to its original shape. That moment is what marks the transition from elastic to plastic behavior.

The other options don’t fit as this transition isn’t defined by the maximum elastic strain, zero strain, or the ultimate tensile strength. The ultimate tensile strength occurs later, after plastic deformation has already progressed and necking begins.