Force-extension graph shows elastic and plastic deformation phases

Steps:

• Linear rise from origin indicates elastic region following Hooke's law (F = kx).
• Deviation from linearity marks yield point where plastic deformation begins.
• Continued rise post-yield shows work hardening.
• Plateau indicates constant force during extensive plastic flow or necking.

Why D is correct:

• Plateau represents yield plateau in ductile materials, where stress remains constant during dislocation movement (per plasticity theory).

Why the others are wrong:

• A: Ignores plastic phase; graph shows beyond elastic limit.
• B: Slope doesn't remain constant throughout; it decreases after yield.
• C: No fracture shown; plateau indicates ongoing deformation, not breaking.

Final answer: D