The influence of 3D microstructural features on the elastic behaviour of Tow-Based Discontinuous Composites

Abstract Tow-based discontinuous composites consist of carbon-fibre tows dispersed in a polymeric matrix, resulting in a complex microstructure with inherent 3D features such as tow waviness, non-uniform tow thickness, and fibre content variations; however, most models for these materials are based on 2D formulations, or in very computationally-expensive FE models. This work proposes a computationally-efficient microstructure generator able to recreate the 3D features of tow-based discontinuous composites, coupled with an analytical stiffness model able to quantify the effect of tow waviness on the modulus of these materials, for the first time in the literature. The features of the microstructures generated are validated against 3D measurements obtained through micro-CT scans and optical micrographs. The results of the stiffness model are successfully validated against experimental results from the literature, showing that tow waviness can trigger a knock-down of over 20% on the stiffness of tow-based discontinuous composites. It is also shown that current testing standards can lead to uncertainties over 20% on the measurement of the Young’s modulus of tow-based discontinuous composites, and alternatives to define suitable experimental campaigns are proposed.