Stress and Strain (Engineering Science)

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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
Types of simple stress

Types of simple 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.


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

Types of strain

Types of 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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