Towards a multiscale model for flax composites from behaviour of fibre and fibre/polymer interface

The foundations for a multiscale numerical framework for composites, that can assist in the design of composites structures, have been laid in this study. Fibre tensile and shear properties were investigated experimentally, and subsequently modelled using the laminate theory. The interface properties of a flax/polypropylene and a flax/epoxy system were determined using microbond tests combined with micromechanical models, and properties from transverse tensile tests. These properties were used in numerical models of the microbond test, and good agreement with experiments was obtained for both systems. When the interface and fibre properties were used in numerical models of single flax yarns impregnated with polypropylene or epoxy resin, the stiffness behaviour showed good agreement with experiments for flax/polypropylene and flax/epoxy systems. The peak stress prediction from the flax/polypropylene numerical model was only 6.2% lower than the experimental average of 24.33 MPa. The flax/epoxy model, however, predicted a peak stress value of 85.6 MPa which was 20.6% higher than the experimental value of 70.9 MPa. The properties obtained from this study, along with the methodology, can be used to estimate macro-scale strengths of composite members in structures for different layups and loading conditions.