Development of numerical and experimental methods and processes for the gentle manufacturing of hybrid yarns from recycled carbon fibres with a large fibre length distribution for thermoplastic composites

• Applicants: Professor Dr.-Ing. Chokri Cherif; Dr. Thomas Gereke
• Subject Area: Lightweight Construction, Textile Technology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407164652

Compared to the mechanical properties of composites from recycled carbon fibres (rCF) based on moulding compounds and nonwovens, hybrid yarns from rCF and thermoplastic fibre with adjusted yarn properties offer an excellent potential for high fibre orientation, fibre length, com-pactness, high fibre volume content resulting in a high level of performance in composites. However, the spinning of hybrid yarns from rCF and thermoplastic fibres for carbon fibre rein-forced composites (CFRP) is based on modified flyer and wrap spinning technologies with high yarn twists, which are indispensable to ensure sufficient yarn strength and a stable spinning process. Nevertheless, high yarn twist results in undefined damage of the rCF during spinning and low fibre alignment in the composite. Further challenges are high fibre damage during processing rCF and the resulting high short fibre content in fibre structures. These lead to low mechanical properties of CFRP and irreproducible manufacturing processes. Due to the in-creasing trend towards the use of thermoplastic CFRP, there is a high demand for the efficient manufacturing of twist-free and low-damage yarns from rCF with high quality in order to achieve a sustainable solution for exploiting the potential of rCF in CFRP. For this purpose, the fundamentals of the simulation-supported as well as measurement-accompanied carding and drawing process for a gentle processing of rCF are to be developed and a new twist free yarn formation process and associated technology are to be developed. Therefore, one of the main objectives of the project is fibre structure analyses, numerical and experimental investigations on the gentle processing of rCF (fibre volume content up to 65%) in combination with thermoplastic fibres enabling high tensile strength and Young’s modulus in composites (same or more than 95% compared to those of virgin CF filament yarns). For this purpose, a method and fast algorithm for the measurement of online fibre length, orienta-tion distribution and level of mixing of rCF in real time during carding will be developed for a better understanding and aimed development of the carding process. A simulation of the card-ing process will provide information on the relationships between process parameters, fibre damage and fibre length distribution and serve to systematically design the process and card-ing machine modifications in such a way that a sliver can be produced gently with high uni-formity without trial and error. Furthermore, the innovative core of this project proposal lies in a new spinning process and its implementation for the production of twist-free hybrid yarns from rCF and thermoplastic fibres. Stochastic finite element models will predict yarn and com-posite parameters to establish relationships between fibre and process parameters and yarn and composite properties. As a result, the potential of rCF to achieve high mechanical proper-ties of CFRP will be explored.

• DFG Programme: Research Grants