A critical review of the ultrastructure, mechanics and modelling of flax fibres and their defects

Prompted by environmental legislation and citizens' awareness induced by global warming effects, the market for plant-fibre reinforced composites has been growing steadily for the past 10-20 years, as observed by the substantial increase in academic and industrial research developments. However, the transition to larger production still requires several uncertainties to be overcome. Among these uncertainties, defects in plant fibres are known to decrease the mechanical properties at the composite scale. It is therefore of interest to better understand the defects nature, origin and consequences at the fibre scale to monitor the use of plant fibres as reinforcement. In recent decades, finite element modelling has emerged in various scientific fields as an interesting tool that complements experimental characterization. Finite element modelling is even more critical for small and intricate elements such as plant fibres where standard mechanical tests require substantial adjustments and investments due to their complex ultrastructure compared to synthetic materials. The main objective of this review is to provide a novel overview of defects found in plant fibres and their influence on the mechanical properties of plant fibres based on experimental and modelling work. Through a top-down and multi-scale approach, we first describe the flax fibre ultrastructure with a focus on defects. Then, advanced testing methods and emerging numerical approaches that capture the complex mechanical behaviour of plants, especially flax fibres, are addressed.

Automated summary

The market for plant-fibre reinforced composites has been growing steadily due to environmental legislation and global warming effects, but uncertainties regarding defects in plant fibres decrease mechanical properties at the composite scale. Finite element modelling has emerged as a crucial tool in understanding these defects, particularly in complex plant fibre ultrastructures compared to synthetic materials. Through a top-down and multi-scale approach, this review addresses advanced testing methods and numerical approaches to capture the complex mechanical behaviour of plant fibres.