Ratio of lateral contraction to linear elongation is called Poisson’s ratio. It can also be defined as the ratio of unit transverse strain to unit longitudinal strain.
The formula for Poisson’s ratio ‘σ’ is given as,
Poisson’s ratio = σ =Lateral contraction / Linear elongation.
or
Poisson’s ratio = σ = – εt / εl ——— where εt = transverse strain and εl = longitudinal strain
The decrease in thickness in lateral direction is lateral contraction and extension in length is known as linear elongation.
