No abstract

PACS 62.20.Dc, 81.05.ZxThe 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 ν 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 [± β/± θ] s angles were investigated for carbon fibre laminates and it was found that auxetic behaviour could be generated for β up to 45°. 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 β layers other than the 0° and 90° previously investigated).

Honeycomb structures are essentially constituted of a repetition of regularly-arranged and loaded sub-structures. The present study carries out a parametrically investigation of the behavior of a multi re-entrant honeycomb structure with variable stiffness and Poisson's ratio effects. A refined analytical model is specifically developed and compared to full-scale numerical simulations. The analytical model developed is based on energy theorems and takes into full consideration bending, shearing and membrane effects. The influence of the cell walls thickness on the elastic homogenized constants is investigated. The results obtained show a good agreement between the refined analytical approach developed and the numerical computations carried out.

This work is concerned with the influence of carbon fibre, resin types and fibre volume fraction on the through the thickness Poisson's ratio of composite laminates. Different types of carbon fibres in various resins with several fibre volume fractions ranging between 65 and 80% are analysed to show the effect of each parameters on the values of the Poisson's ratios ν13 of the laminates balanced of the type [±θ]2S.

This paper is focused on the identification of the in-plane elastic constants of a new design of auxetic (negative Poisson's ratio) honeycomb configuration with curved cell walls by using analytical and numerical homogenization techniques. The sensitivity of the elastic constants is determined against the various cell geometry parameters. Good agreement between the analytical and numerical simulations is observed. We show that the specific curved wall honeycomb configuration proposed in this paper possesses a high in-plane shear compliance, tailored anisotropy and the possibility of inducing a negative Poisson's ratio behaviour in baseline honeycomb configurations that would have otherwise positive inplane Poisson's ratios.