Poisson's Ratio

ϵ^{'} = - v ϵ

v = - \frac{transverse strain}{axial strain}

where $v$ is Poisson's ratio.

Remains constant in the elastic range
Changes when material deformation is nonlinear (called contraction ratio)

Material	Elastic Modulus (E) (GPa)	Shear Modulus (G) (GPa)	Poisson's Ratio (v)
Aluminum Alloys	70-79	26-30	0.33
2014-T6	73	28	0.33
6061-T6	70	26	0.33
7075-T6	72	27	0.33
Concrete (Compression)	17-31		0.1-0.2
Glass	48-83	19-35	0.17-0.27
Plastics
Nylon	2.1-3.4		0.4
Polyethylene	0.7-1.4		0.4
Rubber	0.0007-0.004	0.0002-0.001	0.45-0.50
Cork			0
Steel	190-210	75-80	0.27-0.3
Tungsten	340-380	140-160	0.2