Strain:-
The ratio of the change in configuration (i.e., shape, length or volume) to the original configuration of the body is called strain. i.e.,
Strain = Change in configuration/Original configuration
It has no unit.
Types of strain:- There are three types of strain:
(i) Longitudinal strain:-
This type of strain is produced when the deforming force causes a change in the length of a body. It is defined as the ratio of the change in length to the original length of the body.
Consider a wire of length L. When the wire is stretched by a force. F then let the change in length of the wire is ΔL (Fig).
Longitudinal strain = Change in length/Original length
or, Longitudinal strain = ΔL/L
(ii) Volume strain:-
This type of strain is produced when the deforming force produces a change in volume of the body (Fig). It is defined as the ratio of the change in volume to the original volume of the body.
If ΔV = change in volume
V = original volume
Volume strain = ΔV/V
-ve sign shows that volume decreases when pressure (i.e., force/area) increases.
(iii) Shear strain:-
This type of strain is produced when the deforming force causes a change in the shape of the body. It is defined as the angle (θ) through which a face originally perpendicular to the fixed face is turned on which a tangential force is applied. (Fig).
