Experimental and numerical approach to understand the role of defects in damage mechanisms of flax fibers at bundle scale

Abstract

Flax fibers represent a valuable reinforcement in composite materials. However, the presence of defects known as kink-bands in flax fiber has the capacity to influence their mechanical properties. The primary objective of this research is to gain a comprehensive understanding of the damage mechanism in flax fiber bundles presenting a novel aspect due to the intricate structure of bundle fibers, which is more complex compared to elementary fibers. The study specifically explores flax fiber bundles under tensile loading and investigates the impact of kink-bands on their failure through a combined approach, utilizing both experimental and numerical methods. In the experimental part, X-ray microtomography in situ tensile testing is carried out, which reveals complex failure mechanisms. Furthermore, a 3D-Finite Elements (FE) model is implemented utilizing 3D reconstructed fiber and used for numerical tensile analysis. Our findings highlight that the kink-band region acts as prominent failure site in fiber bundles with significant stress concentration at the kink-band region, mainly induced by local porosity.