## Stress and Strain (Engineering Science)

## Stress

**Stress** is the internal resistance which the body offers against a load or an external force.

There various types of stresses classified as follows :

- Simple or direct stress – this includes tension, compression and shear.
- Indirect stress – this includes bending and torsion.
- Combined stress – a combination of direct and indirect stress.

### Simple Stress

It is usually called direct stress because it develops under direct loading conditions. There are 3 types of simple stress:

- Tensile stress
- Compressive stress
- Shearing stress

The formula for calculating stress is:

$latex \displaystyle Stress\ = \frac{Force}{Cross-sectional\ Area}$

Whereby Stress is in Newton per square metre (N/m^{2}) or Pascals (Pa) if Force is in N and Area is in m^{2}.

## Strain

The strain (e) is a measure of the deformation of a material under stress. There are three main types of strain:

- Tensile Strain
- Compressive Strain
- Shear Strain

### Tensile Strain and Compressive Strain

Calculations for shear strain are beyond the scope of this post, however, tensile strain and compressive strain are calculated as follows:

$latex \displaystyle strain = \frac{extension}{original\ length}$

$latex \displaystyle strain = \frac{e}{l}$

Both extension and original length must be in the same units. This makes strain is a ratio, which means it has no units. However, strain is sometimes expressed as a percentage by multiplying it by 100. For example, a strain of 0.15 is equivalent to 15%.