Plastic deformation features a non-linear force-extension curve after the yield point

Steps:

• Identify elastic region: initial linear increase in force with extension, following Hooke's law.
• Locate yield point: transition where extension rises without proportional force increase.
• Confirm plastic region: permanent deformation shown by curve bending and hysteresis on unloading.
• Select graph with clear elastic limit followed by extended non-linear plateau or curve.

Why D is correct:

• It displays the yield point and subsequent non-linear region where extension continues with little force increase, defining plastic deformation per material science principles.

Why the others are wrong:

• A: Shows only linear elastic behavior with no yield or plastic region.
• B: Exhibits elastic loading then sudden brittle fracture, lacking plastic flow.
• C: Demonstrates unloading within elastic limits, with full recovery and no permanent deformation.

Final answer: D