Exploration of high and negative Poisson's ratio elastomer‐matrix laminates

Abstract

AbstractElastomer‐matrix composites show promise for high Poisson's ratio and negative Poisson's ratio (auxetic) applications due to high orthotropy. There are approximately five orders of magnitude between the axial stiffness of high modulus graphite fibres and the stiffness of low durometer elastomers. Although the maximum Poisson's ratio for isotropic elastomers is 0.5, it is easily shown that inplane Poisson's ratios twice unity can be obtained with a graphite/epoxy angle‐ply laminate at 25°. Chou and others have predicted inplane Poisson's ratios greater than 7 for certain cord‐rubber combinations. Peel previously predicted inplane Poisson's ratios higher than 32 and less than –60. Preliminary experimental results have produced inplane Poisson's ratios as high as 14. Certain combinations of un‐balanced highly orthotropic laminates may also produce inplane negative Poisson's ratios. Inplane Poisson's ratios, experimentally obtained from two laminate configurations with approximately the same axial stiffness are compared. A symmetric, balanced laminate produced an inplane Poisson's ratio of 3.7; while an unbalanced laminate with an equivalent axial stiffness produced an average inplane Poisson's ratio of –1.5. Certain high and negative Poisson's ratio elastomer‐matrix laminates appear to have quasi anti‐symmetric relationships about 0°, although laminate designers may consider dual angle‐ply laminates to be the more likely counterpart to the unbalanced dual angle auxetic laminates. Unbalanced symmetric laminates experience significantly more inplane shear deformation when axially loaded than their balanced counterparts. The high shear may be desirable for damping applications, but less desirable otherwise. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)