# Deformation versus Strain

• Post by:
• August 7, 2021

Deformation is the changing of the shape of a body due to the forces and pressure applied to it. Strain is the force created by the elasticity of an object.

Both deformation and strain are two very important concepts discussed under material science. These concepts are vital in the course of understanding subjects such as material science, mechanical engineering, civil engineering, and even biological sciences. The contribution of deformation and strain to these sciences is enormous, and these concepts are vital to excel in these fields.

### Strain

When 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 to try to resist the deformation. This force is known as strain. This effect can be explained using the potential energy of the bonds. The bonds inside a material act like small springs. The neutral position or the equilibrium position of the atom is when there is no force acting on the object. When a force is applied the bonds are stretched or contracted. This causes the potential energy of the bonds to get higher. The potential energy created by this in turn creates a force, which is opposite to the applied force. This force is known as the strain.

### Deformation

Deformation is the change of the shape of any object due to the forces acting upon it. Deformation comes in two forms. They are namely elastic deformation and plastic deformation. If a graph of stress versus strain is plotted, the plot will 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. Hooke’s law states that for the elastic range of the material, applied stress is equal to the product of 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 to which it becomes a 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. Plastic deformation is sometimes known as irreversible deformation, but actually, some modes of plastic deformation are reversible.

### Summary

• Strain is force, whereas deformation is the change of shape.
• Strain is a measurable quantity whereas deformation is not measurable.
• The strain on an object strictly depends on the external force applied. The deformation of an object depends on the external force, the material, and whether the material is in an elastic deformation or a plastic deformation.

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