Interfaces within a Flax Fibre Based Composite: Characterisation and Modelisation

As flax fibres exhibit good mechanical properties and low cost, they are more and more considered, since the early 2000’s, as efficient reinforcement for polymer based composites in replacement of E-glass fibres in automotive or building areas. The properties of the elementary fibres are now relatively well-known (strength comprised between 600 and 2000 MPa, Young’s modulus around 50 GPa and failure strain about 2% [1,2]), but information about the mechanical behaviour of the interface between the fibres of a flax bundle is still missing. However, this phase is of crucial importance when modelling the global deformation of the derived composites, since the estimation of mechanical properties of a fiber bundle without taking into account the behaviour of interfaces leads to an overestimation of these properties. The only mechanical information available for flax bundles is their strength, evaluated at 500 MPa for gauge length above 20 mm [3,4]. A possible explanation for this lack of data may be the very small dimensions of these interfaces (less than 1 μm wide) and the minute section of the elementary fibres (around 20 μm in diameter) [5,6].