Strain

Axial Strain

ϵ = \frac{δ}{L_{0}} = \frac{L_{f} - L_{0}}{L_{0}}

\epsilon =\lim_

ϵ^{'} = \frac{δ^{'}}{D_{0}} = \frac{D_{f} - D_{0}}{D_{0}}

Change in angle between two line segments originally perpendicular

γ_{n t} = \frac{π}{2} - lim_{\begin{matrix} B \to A along n \\ C \to A along t \end{matrix}} θ^{'}

$ϵ^{'} = - v ϵ$
$v = - \frac{transverse strain}{axial strain}$

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