Poisson ratio is the used to measure the Poisson effect. which is the phenomenon of the behaviour of the material tends to expand in the perpendicular direction to the applied load. Here is the straight definition of the Poisson ratio

Mathematically Poisson ratio is expressed as the ratio of Lateral strain to its Linear (Longitudinal) Strain

When a material is subjected to loading, within the elastic limit, then the ratio of lateral strain to it’s to the Linear(longitudinal) strain is constant. This ratio is called **Poisson’s ratio**.

It is Denoted by “**µ**”

The Poisons ratio value ranges from** 0.1 to 0.5 **

## Understanding Poisson’s ratio

Consider a rod of length L, Diameter D and two forces acting at the ends of the Rod as shown in the figure. Then there would be deformation in the length and the diameter of the rod.

See the Gif image below. The changed Length and diameter would be **Δ**L and **ΔD **respectively.

Then,

**Lateral Strain** is the ratio of Change in diameter(**ΔD**) to its original diameter(**D**).

In Pull type of load, the diameter goes on decreasing, so it will be negative(-ve).

**Linear(Longitudinal) Strain** is the ratio of Change in Length(**Δ**L) to original length (**L**).

In Pull type of load, the length goes on increasing, so it will be negative(+ve).

## Poisson ratio of some Important Material

Steel’s Poisson ratio = **0.29**

Stainless steel’s Poisson ratio= **0.3**

Aluminium ‘s Poisson ratio= **0.35**

Copper Poisson ratio= **0.37**

Lead Poisson ratio= **0.44**

Rubber Poisson ratio= **0.48 to 0.5**

Cork poisson’s ratio= **0.5**

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