Comparison of Experimental and Calculated Tensile Properties of Flax Fibres

Abstract

The tensile properties of natural plant fibres are commonly determined by single fibre testing. The cross-sectional area used to determine the modulus and strength is usually obtained by measuring the fibre width and using this as the fibre diameter on the assumption that the fibres are circular in section. The assumption of circularity is reasonably true for synthetic fibres but is not correct for natural fibres, and this can lead to a substantial error when determining the tensile properties of the fibres. The incorporation of a fibre area correction factor, which takes into account the non-circularity of natural fibres, has been proposed by earlier workers, who used it successfully to predict the mechanical properties of jute fibre composites. The aim of the present study was to evaluate the wider applicability of this methodology by applying it to flax fibre composites. The work involved determination of the tensile properties of 113 flax technical fibres using an experimentally determined fibre area correction factor to account for the non-circularity of the fibres. The data were then compared with those obtained from back-calculation of the results obtained from longitudinal tensile testing of flax/vinyl ester unidirectional composites manufactured utilising identical fibres to those used in the single fibre tests. Account was taken of the effect of fibre length on strength. The experimentally determined fibre area correction factor was found to be 2.70. Taking this into account for the single fibre tests, the back-calculated modulus of the flax fibres was within 6% of that obtained from the single fibre tests, while the strength was within 7%.

Keywords

• natural fibre composites
• flax fibres
• flax/vinyl ester
• single fibre tensile testing
• fibre area correction factor