Elastic deformation is a temporary and reversible change in the shape or size of a material that disappears when the applied external force is removed. It occurs due to the stretching or bending of atomic bonds within the material, which can withstand stress without breaking. The ability of a material to return to its original shape after deformation is called elasticity. During elastic deformation, the bond stretching is only temporary, and atoms return to their original positions once the stress is removed. However, with repeated stress over time, a material may lose its elasticity, become brittle, and lose its ductility.
Elastic Substances:
Elastomers such as vulcanized rubber are the greatest examples of elastic bodies. Vulcanized rubber has a polymer structure that is cross-linked. Sulphur bridges exist between polymer chains. These sulfur cross-links improve rubber flexibility by allowing it to endure stress.
The stress-strain curve for a ductile material is seen in the figure above. Consider the metal copper. The elastic zone depicts the extent to which the elastic deformation occurs. After reaching the elastic limit, the material will experience plastic deformation, which is a permanent distortion.
Plasticity
Plastic deformation is the permanent and irreversible change in the shape or size of a solid material that occurs when the applied stress exceeds its elastic limit. In this process, some atomic bonds break, and atoms slip past one another, leading to a permanent rearrangement of the internal structure. As a result, the material does not return to its original shape after the removal of the applied force. This property of a material to undergo permanent deformation is known as plasticity, which allows materials to be shaped into desired forms.
Plastic Substances:
Metals, polymers, rocks, and many other materials exhibit plasticity to varying degrees. Plastic deformation mainly occurs in ductile materials such as copper and other metals when the applied stress exceeds their elastic limit. In contrast, brittle materials like rocks generally show very little or no plastic deformation before fracture. Plastic deformation plays a crucial role in manufacturing processes such as forging, rolling, and heat treatment, where materials are permanently shaped into useful products. The response of a material to an applied force depends on its elastic and plastic properties. Elastic materials return to their original shape after the force is removed, while plastic materials undergo permanent deformation.
Difference between Elasticity and Plasticity
Elasticity | Plasticity | |
| 1. | Elasticity is the property of a solid material that allows it to restore its shape after an external load is removed. | Plasticity is the property of a solid substance that allows it to keep its deformed shape even when the external load is removed. |
| 2. | The amount of external force necessary to bend a solid elastically is quite tiny. | The amount of external force necessary to bend a solid elastically is high. |
| 3. | Hooke’s Law of elasticity is applicable within this elastic region. | Hooke’s Law of elasticity is not applicable within this plastic region. |
| 4. | The stress-strain curve is mostly linear in the elastic region. | The stress-strain curve is non-linear in the plastic region. |
| 5. | Many properties of the solid material remain the same for elastic deformation. | Many properties of the solid material change considerably for plastic deformation. |
| 6. | Elastic deformation occurs before plastic deformation. | Plastic deformation occurs only after the body undergoes elastic deformation. |
| 7. | Here, deformation is reversible. | Here, deformation is irreversible. |
| 8. | Elasticity is used in machine tool structures, Bridges, other civil frames, many household structures that should retain their shape, etc. | Plasticity is used in various forming operations such as rolling, forging, extrusion, etc.; sheet metal working; Rivet joining; etc. |
Applications of Elasticity
- In cranes, the load must not exceed the elastic limit of the rope to prevent permanent deformation or breaking.
- Elasticity helps in calculating the required cross-sectional area and radius of ropes or wires.
- It is used to estimate the maximum possible height of mountains on Earth.
- Elasticity is important in bridge design to ensure the structure does not bend excessively or fail under loads like traffic and wind.