Poission's Ratio

Poission's Ratio :-

 

  When a material is stretched in both direction, it tends to compress in the direction perpendicular (middle) to that of force application and vice-versa this phenomenon is given in terms of Poission's Ratio.

It is the ratio of transverse contraction strain to longitudinal extension strain, in the direction of stretching force for tensile deformation, Possion's Ratio is positive and for compressive deformation it is negative as in negative possion's ratio suggests that the material will exhibt a positive strain in the transverse direction even though the longitudinal strain is positive as well.

Poission's Ratio for concrete increases with richer mixes.

Example:- Take a piece of rubber in the shape of cuboid, then pulling it along the opposite side. what will you see?????

-  When we stretched rubber to both sides then it will compress in the middle. If the original length and breadth of the rubber are taken as L & B respectively, then when pulled longitudinally, it tends to gets to get compressed laterlly. In simple words, length has increased by an amount dL and the breadth has increased by an amount dB.

The formula of Poission's Ratio:- u= Et/El

       Poission's Ratio of different material lies in the range of 0 to 0.5

        Aluminium - 0.32

        Concrete -     0.2

        Cork -           0

        Rubber -       0.49

Poission's ratio for concrete is 0.2 but if the concrete cracks the value is 0.