# Stress and Strain (Engineering Science)

Contents

## 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/m2) or Pascals (Pa) if Force is in N and Area is in m2.

## 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%.

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