ABSTRACT
Auxetic polymers are very exciting materials of multidisciplinary eld. These are advanced materials having extreme properties such as very high strength and very high modulus. In these fascinating materials, the main property is their volume expansion when subjected to tensile load. They possess negative Poisson’s ratio. By auxa, we mean enlargement. So auxetic materials mean enlarging materials. This is just unbelievable as all the known materials (metals, alloys, ceramics, polymers, etc.) elongate in the direction of applied tensile load and contract in other two lateral directions (dimensions). That is why we obtain the 3D stress-strain relations for isotropic materials (non-auxetic) as
ε σ νσ νσx x y zE= − −( ) 1 (2.1a)
ε σ νσ νσy y z xE= − −( ) 1 (2.1b)
ε σ νσ νσz z x yE= − −( ) 1 (2.1c)
where ε and σ are linear strains and stresses, respectively E and ν are modulus of elasticity and Poisson’s ratio x, y, z correspond to three orthogonal axes
These equations indicate that the Poisson’s ratio ν = εy/εx and ν = εz/εx is a positive quantity.
