How do elastic and plastic deformation differ?

Elastic and plastic deformation are two fundamental concepts in materials science that describe how materials respond to applied stresses. The key distinction lies in their reversibility and the stress levels involved.

Elastic deformation refers to the temporary change in the shape or size of a material when an external force is applied. When the stress is removed, the material returns to its original shape and dimensions, which is why this type of deformation is termed "reversible." The relationship between stress and strain in the elastic region follows Hooke's Law, where strain is directly proportional to stress.

On the other hand, plastic deformation occurs when the applied stress exceeds a certain threshold known as the yield strength of the material. In this case, the material undergoes a permanent change in shape or size, meaning that once the stress is removed, the material does not return to its original form. This is why plastic deformation is considered irreversible.

Given this understanding, the correct option highlights the fundamental property that elastic deformation is reversible, while plastic deformation results in permanent alteration of the material's structure.