If a steel plate has a tensile strength of 500 MPa and is subjected to 787 MPa, what happens first?

• A. It fractures immediately
• B. It yields first
• C. It hardens without deformation
• D. It necks first

Answer: (D)

When a ductile steel is pulled, it first yields and then work-hardens up to its maximum sustainable load, the ultimate tensile strength. At that point deformation becomes unstable and localizes into a neck, a narrowing of the cross-section. If the applied load exceeds the tensile strength, the first event you’d see is necking, because the specimen can no longer carry the same uniform cross-section after reaching the maximum load. It does not fracture instantly at 787 MPa; necking occurs first and then leads to fracture as deformation localizes further. Yielding would have happened earlier at a lower stress, and hardening without deformation or immediate fracture don’t describe the actual sequence.