A parametric study on the mesostructure design and stiffness of tow-based discontinuous composites using a voxel finite element model

Tow-Based Discontinuous Composites (TBDCs) are manufactured by compression moulding of randomly deposited carbon fibre tows. As such, a quasi-isotropic response with high stiffness and strength can be achieved, while reducing waste, thus competing with laminated composites. Moreover, novel TBDCs with ultra-thin tows (0.02 mm) have expanded the design space and opened opportunities for thin-walled structures. However, complex 3D mesostructural parameters have been demonstrated to impact their stiffness, such as tow/plate morphology, resin pocket content, tow waviness, and tow orientation distributions, which remain a challenge for their modelling and design. The present work exploits a novel voxel-based finite element mesostructure generator for TBDCs developed and validated by the authors to explore the significance of mesostructural design modifications on their stiffness. A parametric study over an extended design space including baselines of thick, thin, and ultra-thin tow systems, is conducted to investigate the effect of important parameters such as the tow moduli (up to ultra-high modulus), tow and plate dimensions (with attention to thin plates), and preferred in-plane fibre orientation distributions. Also, the significance of the numerical model is compared with short-fibre models and equivalent laminates. The results compare their sensitivity for each TBDC material system, showing opportunities for optimisation. Finally, design constraints are identified in terms of the stiffness knockdown, quasi-isotropic behaviour, statistical variability of the elastic properties, and critical minimum plate dimensions.