Strain

The change produced in the dimensions of a body under a system of forces or couples in equilibrium, is called strain, and is measured by the change per unit length [linear or longitudinal strain], per unit volume [volume strain], or the angular deformation [shear strain or simply shear] according to the change that takes place in length, volume or shape of the body.

Therefore, we have three kinds of strain: (i) Longitudinal strain (ii) Volume strain and (iii) Shearing strain

(i)  Longitudinal strain: The change in length per unit length is called longitudinal strain. That is if L is the original length and l is the change in length, then

 Longitudinal strain = Change in length / original length = l / L

(ii) Volume strain: The change in volume per unit volume is called volume strain. That is if V is the original volume and v is the change in volume, then

Volume strain = Change in Volume / original volume = v / V 

 

(iii) Shearing strain: A change in shape without change in volume is known as shearing strain. It is measured by the angle of shear measured in radians.