Material behavior — term for permanent deformation A structural member that does not regain its original shape after the load causing deformation is removed is said to exhibit which behavior?

Introduction / Context:
Understanding elastic versus plastic behavior is critical in structural design, as permanent deformations affect serviceability and residual capacity after overloads or forming operations.

Given Data / Assumptions:

• The load is removed after causing observable deformation.
• The member does not return to its original dimensions.

Concept / Approach:
Elastic behavior is characterized by full recovery of strain on unloading. Plastic behavior produces permanent (residual) strain. Rigid is an idealized concept implying no deformation at all under load.

Step-by-Step Solution:

Verification / Alternative check:
Typical stress–strain curves for metals show linear elastic region up to yield, followed by plastic region; unloading from plastic region leaves a permanent offset.

Why Other Options Are Wrong:

• Elastic: contradicts the observed non-recovery.
• Rigid: implies zero deformation, inconsistent with the scenario.
• Viscous-elastic only: viscoelasticity involves time-dependent recovery but not necessarily permanent set for purely elastic–viscous models.

Common Pitfalls:
Confusing time-dependent (creep/viscoelastic) effects with plasticity; assuming small residuals are elastic.

Final Answer:
Plastic