Micromechanical analyses of unidirectional (UD) discontinuous flax fiber reinforced composites

Prediction of the strength and damage behavior of natural fiber composites is a challenging task due to computational difficulties resulting from large fiber aspect ratio, non-uniform fiber length distribution, and interface modelling. A computational micromechanical model , which solves the above-mentioned challenges by incorporating a novel representative volume element (RVE) generation algorithm inspired by Lennard-Jones potential, is developed to predict the tensile behavior of unidirectional (UD) flax/epoxy composites. Effects of fiber aspect ratio, fiber spatial distribution, interfacial and matrix properties on longitudinal modulus, strength, and the damage behavior of the flax/epoxy composites are extensively studied using the numerical model. The modulus and strength predicted by numerical model were compared with both analytical models and experimental results, which not only validated the numerical model but identified the limitations of analytical model. The longitudinal strength of flax/epoxy composites initially increased with fiber aspect ratio. Upon reaching certain fiber aspect ratio (25 in this study), strength predicted by both RVE (RVEs with many fibers) and unit cell (unit cells with two fibers) are close to experimental value (240 MPa). This finding provides confidence and guidance on how to use simplified unit cells to predict the strength of natural fiber composites with acceptable accuracy and much lower computational cost. • An advanced micromechanical model based on RVE method is developed to study the longitudinal tensile behavior of DFRCs. • Rich longitudinal tensile behaviors of DFRCs are comprehensively studied using the proposed micromechanical model. • Strength of DFRCs increases with the increase of inter-fiber overlapping length until reaching a constant value. • The numerical model is validated by experiment and compared with analytical predictions proving its accuracy and merits. • Simplified RVEs with large fiber aspect ratio (≥30) can predict the strength upper bound for DFRCs with acceptable accuracy.