Question

is poission's ratio an elastic modulus???

Answer 1

Definition of Poisson's ratio 
Poisson's ratio is the ratio of transverse contraction strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio. Poisson's ratio, also called Poisson ratio or the Poisson coefficient, or coefficient de Poisson, is usually represented as a lower case Greek nu, n. 
If your browser does not interpret Symbol font properly, Greek nu, nmay instead look like a bold face Latin n

Answer 2

The Poission's ratio of a stable, isotropic, linear elastic material will be greater than - 1.0 or less than 0.5 because of the requirement for the Young's modulus, the shear modulus and bulk modulus to have positive values. Most materials have Poission's ratio value ranging between 0.0 and 0.5

Poission's ratio is defined as the ratio of laterial strain to the longitudinal strain.

Poission's ratio=Laterial strain/Longitudinl strain
Sigma = -∆R/R / ∆L/L

Poission's ratio is denoted by 'Sigma'

1) Poission's ratio is unitless and dimensionless. Where, negative sign indicate thats if length increases then radius is decreases.
2) It is theoretically volume is lies in between -1 and 0.5 but practically value lies in 0 and 0.5