Plastic Deformation: Permanent Change in Shape

Steps:

• Recall that deformation in materials is either elastic (reversible) or plastic (irreversible).
• Elastic deformation follows Hooke's law up to the yield point, allowing return to original shape.
• Beyond the yield point, plastic deformation occurs, causing permanent changes.
• Identify the choice matching permanent non-recovery after force removal.

Why B is correct:

• Plastic deformation is defined as the irreversible straining where the material does not return to its original length upon removal of the load, per standard mechanics of materials.

Why the others are wrong:

• A: Plastic deformation occurs beyond Hooke's law limit, in the nonlinear region.
• C: Initial plastic deformation may follow Hooke's law until yield, so it sometimes obeys it.
• D: This describes elastic deformation, not plastic.

Final answer: B