What is the Difference Between Elastic and Plastic Deformation?

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The main difference between elastic and plastic deformation lies in the material's ability to return to its original shape after undergoing a change in shape or size due to external forces.

  • Elastic Deformation: This type of deformation occurs when a material can return to its original shape after the force causing the deformation is removed. The material has a specific amount of force or pressure for which it deforms elastically. Elastic deformation is reversible, meaning that no permanent change in the material's shape or size occurs. Examples of elastic deformation include the vibration of seismographs during earthquakes and the bending of rock layers under compression.
  • Plastic Deformation: This type of deformation happens when a material undergoes an irreversible change in shape or size when exposed to a stress that exceeds its elastic limit. When energy goes into changing the shape of a material and it stays changed, that is said to be plastic deformation. Some common examples of plastic deformation include the folding and faulting of rock layers under compression, the stretching and thinning of rock layers under tension, and the compaction and hardening of sedimentary rocks. Materials that have a lot of plastic deformation before breaking are said to be ductile, while those that can't stretch or bend much without breaking are called brittle.

In summary, elastic deformation refers to the temporary change in a material's shape that reverts back to its original form when the force is removed, while plastic deformation refers to the permanent change in a material's shape that does not revert back to its original form after the force is removed.

Comparative Table: Elastic vs Plastic Deformation

Here is a table summarizing the differences between elastic and plastic deformation:

Feature Elastic Deformation Plastic Deformation
Definition Temporary and reversible deformation that occurs when an external force is applied. Permanent deformation that occurs when the external force is applied.
Recovery The material regains its original shape when the external force is removed. The material retains its deformed shape even after the removal of the external force.
Stress-Strain Relationship Linear and proportional to the applied stress. Non-linear and not proportional to the applied stress.
Effect on Crystal Lattice Structure Temporary distortion of the lattice structure that is proportional to the applied stress. Permanent shift in the lattice structure due to the applied stress.
Mechanical Properties Mechanical and metallurgical properties of the solid material remain unaltered. Many properties of the solid material change considerably.
Examples Stretching a spring or pulling a rubber band. Permanently deforming a piece of metal by bending or compressing it.

In summary, elastic deformation is a temporary and reversible change in the shape of a material when an external force is applied, while plastic deformation is a permanent change in the shape of a material under the same conditions. When the external force is removed, an elastically deformed material returns to its original shape, but a plastically deformed material retains its deformed shape.