A study of the tensile behaviour of flax tows and their potential for composite processing

• Flax tows are characterised by tensile testing under various conditions.
• The tensile properties and their dispersion are dependent on the gauge length.
• The distribution of the fibres length in specimens commands the tensile behaviour.
• Packs of fibre bundle debonding failure mode are observed by image correlation.
• Interesting tensile properties are obtained on epoxy impregnated and cured tows.

To study the potential of flax tows in composite processing as an alternative to flax spun yarns, a flat flax tow consisting of aligned fibre bundles held together by a natural binder was used and characterised in tension under various conditions. The effect of the gauge length was studied on the dry reinforcement. The experimental results showed that the mechanical properties and failure mechanism varied significantly depending on the gauge length and are discussed in relation to the distribution of elementary fibres within the tow. A characteristic length as from which the mechanical properties are stable has been identified. At this length, the effect of the strain rate on the tensile properties was measured and their sensitivity to the strain rate suggests a viscous effect in the behaviour of the flax tow. To approach process conditions such as wet filament winding, a batch of specimens was impregnated with epoxy prior to tensile testing. The tensile properties under wet conditions were found to be close to the properties under dry conditions and shows that the tow can withstand typical processing tensions. Finally, tensile tests on cured-impregnated tows showed interesting mechanical properties for composite application.