# STRENGTH OF MATERIALS [MECHANICS OF SOLIDS]

When an external force acts on a body, the body tends to undergo some deformation. Due to cohesion between the molecules, the body resists deformation. This resistance by which material of the body opposes the deformation is known as strength of material. Within a certain limit (i.e., in the elastic stage) the resistance offered by the material is proportional to the deformation brought out on the material by the external force.

Also within this limit the resistance is equal to the external force (or applied load). But beyond the elastic stage, the resistance offered by the material is less than the applied load. In such a case, the deformation continues, until failure takes place. Within elastic stage, the resisting force equals applied load. This resisting force per unit area is called stress or intensity of stress.

When a body is subjected to some external force, there is some change of dimension of the body. The ratio of change of dimension of the body to the original dimension is known as strain. Strain is dimensionless.
Strain may be :
1. Tensile strain, 2. Compressive strain,
3. Volumetric strain, and 4. Shear strain.

If there is some increase in length of a body due to external force, then the ratio of increase of length to the original length of the body is known as tensile strain. But if there is some decrease in length of the body, then the ratio of decrease of the length of the body to the original length is known as compressive strain. The ratio of change of volume of the body to the original volume is known as volumetric strain. The strain produced by shear stress is
known as shear strain.