Natural Fibre Cross Sectional Area, Its Variability and Effects on the Determination of Fibre Properties

The results of a study on the measurement of fibre bundle cross section and its variability in flax and sisal fibres are presented. Cross section values obtained from “diameter” measurements were more than double the values obtained from actual observation of cross sections of the same individual fibre bundles. The overall conclusion is that “diameter” measurement is not an attractive method for accurate estimation of cross sectional area of these natural fibre bundles. This conclusion is significant for researchers engaged in micromechanical investigation of natural fibre composites since differences in fibre cross section translate directly into differences of the same magnitude in the values obtained for the fibre modulus and strength. The error in fibre bundle cross section introduced by the “diameter” method scales with the average fibre bundle “diameter” which may also result in erroneous observations of fibre modulus and strength which scale inversely with natural fibre bundle “diameter.” The difference in average cross section observed from fibre bundle to fibre bundle was significantly greater than the variation along the length of each individual fibre bundle. The minimum to maximum cross section variability of individual flax fibre bundles was found to be approximately twice that observed for sisal fibre bundles. A simple model based on a non-circular fibre bundle cross section is introduced and shown to explain these observations.