Characterisation of the transverse thermoelastic properties of natural fibres used in composites

To predict the properties of a composite, it is necessary to identify the properties of the constituent materials, especially those of the fibre. Mechanical properties of natural fibres (NF) are anisotropic and cannot be characterised in the same way as isotropic materials. Therefore further characterisation of the natural fibres is needed to determine their transverse thermo-mechanical behaviour. An understanding of the thermoelastic anisotropy of natural fibres is important for defining their performance in potential composite applications. In this study, thermoelastic properties of flax and sisal fibres where determined through a combination of experimental measurements and micromechanical modelling. Dynamic mechanical thermal analysis and thermal mechanical analysis techniques were employed to characterise model unidirectional NF-epoxy composites over a range off-axis loading angles. These results were input into a number of micromechanical and semi-empirical models to determine the transverse and longitudinal thermoelastic properties of the fibre. The results confirm the high degree of anisotropy in properties of the flax and sisal fibres.