Modelling the influence of the orientation and fibre reinforcement on the Negative Poisson's ratio in composite laminates

The variation of through-thickness Poisson's ratio with fibre type and orientation has been investigated using a specially developed Fortran program. Glass fibre/epoxy resin composites were always found to be conventional, but negative Poisson's ratio values of up to nu(13) = -0,746 were produced over certain orientation angles for Kevlar and carbon reinforcements. This underlines the need for anisotropic pre-preg material. A range of [+/-beta/+/-theta](s) angles were investigated for carbon fibre laminates and it was found that auxetic behaviour could be generated for beta up to 45 degrees. All the findings of this work have extended the range of laminates which can be engineered to be auxetic either by material (i.e. Kevlar as well as carbon) or by orientation (i.e. by introducing further beta layers other than the 0 degrees and 90 degrees previously investigated). (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.