Designing Stiff and Tough Biocomposites by Hybridization of Flax and Silk Fibres: Scrutinizing the Effects of Fibre Ratio and Laminate Lay-up Configuration
Topic(s) : Material science
Co-authors :
Alexandros PRAPAVESIS (BELGIUM), Weijing WU , Penelope KOPANA (BELGIUM), Kobe SCHILDERMANS (BELGIUM), Yasmine MOSLEH (NETHERLANDS), Aart Willem VAN VUUREAbstract :
Flax fibre composites offer a sustainable alternative to traditional synthetic fibre reinforced composites. Known for their relatively high stiffness and strength along with a low density, these composites find applications in industries such as automotive and construction, combining performance with eco-friendliness. As the demand for sustainable bio-based solutions grows, flax fiber composites present a compelling option for diverse applications. However, flax fibre composites have limited impact resistance and toughness due to the intrinsic brittleness of the reinforcing fibres reaching a tensile strain at failure in the range of 1%-2%. On the other hand, silk, a protein-based (animal) natural fibre, exhibits high ductility reaching a strain to failure of ~20% resulting in outstanding toughness and damage tolerance. This study explores the development, design and optimization of flax-silk fibre interlayer hybrid composites as a sustainable and eco-friendly alternative for advanced material applications. The combination of these two natural fibres can lead to stiff, strong and tough composite laminates due to the synergy between the constituents through controlled damage mechanisms (initiation and evolution).
Hybrid composites were manufactured using flax fibre to total fiber volume fraction ratios of 15%, 35%, and 59% as well as different lay-up configurations to evaluate the effect of damage dispersion on the tensile, bending and impact properties. By optimizing these two parameters, pseudo-ductility and gradual flax fragmentation was observed which lead to an improved ductility of hybrids compared to the flax fibre mono composites, hence resulting in ductile hybrid composites with gradual damage development. Furthermore, the results highlighted an increase in the apparent failure strain of the flax fibres when incorporated in the hybrid systems. This was explained by the residual thermal stresses arising from the mismatch between the coefficients of thermal expansion of the two fibres after specimen manufacturing. Additionally, a positive hybrid effect was observed for tensile strength where the experimental measurements seemingly outperformed the expected strength calculated using a bilinear rule-of-mixtures, thus showing a synergistic effect. In bending and impact, the positioning of the plies remarkably affected the measured properties as placing the flax layers on the outside drastically affected the bending stiffness and strength of the hybrid composite due to the inherent stress distribution in bending. X-ray computed tomography (XCT) was used to characterize the damage mechanisms in mono and hybrid composites where systems with strongest hybrid effect and/or pseudo-ductility were further emphasized.
Hybrid composites were manufactured using flax fibre to total fiber volume fraction ratios of 15%, 35%, and 59% as well as different lay-up configurations to evaluate the effect of damage dispersion on the tensile, bending and impact properties. By optimizing these two parameters, pseudo-ductility and gradual flax fragmentation was observed which lead to an improved ductility of hybrids compared to the flax fibre mono composites, hence resulting in ductile hybrid composites with gradual damage development. Furthermore, the results highlighted an increase in the apparent failure strain of the flax fibres when incorporated in the hybrid systems. This was explained by the residual thermal stresses arising from the mismatch between the coefficients of thermal expansion of the two fibres after specimen manufacturing. Additionally, a positive hybrid effect was observed for tensile strength where the experimental measurements seemingly outperformed the expected strength calculated using a bilinear rule-of-mixtures, thus showing a synergistic effect. In bending and impact, the positioning of the plies remarkably affected the measured properties as placing the flax layers on the outside drastically affected the bending stiffness and strength of the hybrid composite due to the inherent stress distribution in bending. X-ray computed tomography (XCT) was used to characterize the damage mechanisms in mono and hybrid composites where systems with strongest hybrid effect and/or pseudo-ductility were further emphasized.