Elastic vs Plastic Deformation
Deformation is the effect of change in the shape of a physical object when an external force is applied to the surface. The forces can be applied as normal, tangential or torques on the surface. If a body does not change its shape, even slightly due to external forces, the object is defined as a perfect solid object. Perfect solid bodies are not present in nature; every object has its own deformations. In this article, we are going to discuss what elastic deformation and plastic deformation are, how they are encountered in nature, and what are their applications.
When an exterior stress is applied to a solid body, the body tends to pull itself apart. This causes the distance between atoms in the lattice to increase. Each atom tries to pull its neighbor as close as possible. This causes a force trying to resist the deformation. This force is known as strain. If a graph of stress versus strain is plotted, the plot would be a linear one for some lower values of strain. This linear area is the zone in which the object is deformed elastically. Elastic deformation is always reversible. It is calculated using Hooke’s law. The Hooke’s law states that for the elastic range of the material, applied stress is equal to the product of the Young’s modulus and the strain of the material. The elastic deformation of a solid is a reversible process, when the applied stress is removed the solid returns to its original state.
When the plot of stress versus strain is linear, the system is said to be in the elastic state. However, when the stress is high the plot passes a small jump on the axes. This is the limit at which it becomes plastic deformation. This limit is known as the yield strength of the material. Plastic deformation occurs mostly due to the sliding of two layers of the solid. This sliding process is not reversible. The plastic deformation is sometimes known as irreversible deformation, but some modes of plastic deformation are actually reversible. After the yield strength jump, the stress versus strain plot becomes a smooth curve with a peak. The peak of this curve is known as the ultimate strength. After the ultimate strength the material begins to “neck” making unevenness of the density over length. This makes very low density areas in the material making it easily breakable. Plastic deformation is used in metal hardening to pack the atoms thoroughly.
What is the difference between Elastic Deformation and Plastic Deformation?
- The main difference between elastic deformation and plastic deformation is that, elastic deformation is always reversible, and plastic deformation is irreversible except for some very rare cases.
- In elastic deformation the bonds between molecules or atoms stay intact, but only change their lengths; Plastic deformation phenomena, such as plate sliding occurs due to the total fission of the bonds.
- Elastic deformation holds a linear relationship with stress, while plastic deformation holds a curved relationship having a peak.