Answer: Ultimate tensile strength.
- A Elastic limit
- B Yield point
- C Ultimate tensile strength
- D Proportional limit
Correct answer: C. Ultimate tensile strength
Explanation: Necking begins at the ultimate tensile strength, the maximum stress on the curve, after which the engineering stress appears to decrease until fracture even though true stress increases.
A typical stress-strain curve: the initial straight line (Hooke's Law region, slope = Young's modulus) ends at the elastic limit; beyond the yield point, deformation becomes permanent, peaking at the ultimate tensile strength before the wire finally fractures.
Concept context
Stress, strain, Hookes law, and the elastic moduli that describe how solids deform and recover under load.