Which statement about elastic deformation is true?

• A. It results in permanent deformation after unloading.
• B. It occurs only at elevated temperatures.
• C. It involves plastic flow of grains.
• D. After unloading, the material returns to its original dimensions.

Answer: (D)

Elastic deformation is the reversible deformation of a material under stress: the atoms are stretched but not permanently rearranged, so when the load is removed the lattice returns to its original spacing. In this region the stress-strain relationship is roughly linear (Hooke’s law), sigma = E * epsilon, and the applied energy is stored as elastic energy that is released when the load is removed. Because there are no permanent dislocations movements or grain-scale rearrangements, the dimensions recover fully after unloading.

Thus, the statement that after unloading the material returns to its original dimensions is the true one. The other ideas describe behaviors that involve permanent change—like plastic deformation with dislocations, or conditions where elasticity isn’t the governing response (such as at high temperatures or when creep, which is irreversible over time, occurs).