# What is Stress and Strain?

Stress and strain are two important parameters associated with a body that is subjected to an external force.

### Strength of Material

When a body is subjected to some external force, it undergoes some form of deformation. The resistance of the body to prevent such deformation forms the strength of the material.

### What is Stress?

The force of resistance per unit area of the body is called stress. It is measured as the ratio of force and the area of the cross-section. The external force acting on the body is termed as load (P). If the area of cross-section is (A), then stress is given by,

Ïƒ = P/A

### Unit of Stress

The unit of stress is N/m2 or kgf/m2 or kgf/cm2.

The S.I Unit is N/m2. Where, 1N/m2 = 1 PascalÂ

### What is a Strain?

The ratio of change in dimension of the body to its original dimension is called strain. The strain is a unitless quantity. Which is given by the relation,

Îµ = âˆ†l/l
âˆ†l = Change in Dimension
lÂ  Â = Original Dimension

These are of 4 Types:
1. Tensile Strain
2. Compressive Strain
3. Volumetric Strain
4. Shear Strain

#### 1. Tensile Strain

This is the ratio of change in length of the body to its original length due to the deformation caused by a pulling force or tensile force.
e = dl/l

#### 2. Compressive Strain

This is the ratio of change in dimension of the body to the original dimension due to the deformation caused by a pushing force or compressive force.
e = -dl/l

#### 3. Volumetric Strain

This is the ratio of change in the volume of the body to its original volume.
e = dV/V

#### 4. Shear Strain

This is the strain produced due to shear stress.

Shear Strain =Â Î¦= dx/h
 Body Under Shear Stress Fp