Novel 3D tailored discontinuous fibre preforms for a sustainable future in composite manufacturing

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Fibre reinforced polymer composites offer outstanding strength, stiffness and low weight, and their use has increased rapidly in various sectors such as aerospace and automotive. However, the long fibre reinforcements significantly limit the formability of composite materials hence the processability. This fundamental problem can be resolved by changing the reinforcements to short fibres (i.e. a few mm long) provided that the short fibres are highly aligned to minimise the fibre length effect on the mechanical properties of the final parts. Although highly aligned short fibre composites and their manufacturing processes therefore have regained attention, the produced preform is a sheet or tape, and these intermediate materials end up being used as the same way as long fibre reinforced composite fabrication methods: cutting, stacking, forming, and curing. This conventional composite fabrication method still produces a large amount of waste in production even when using aligned short fibre preforms or prepregs. Furthermore, fibre reinforced composite products are prone to crack or fail during post-processes such as drilling or machining. Lack of mechanical properties in the through-thickness direction is also a critical challenge in composite products. The through-thickness reinforcement concept to improve interlaminar shear strength, out-of-plane stiffness, and fracture toughness in fibre reinforced composite materials is not new. However, this has not been achieved yet in a single manufacturing process for aligned short fibre composites. Then, what if highly aligned short and discontinuous fibre composites can truly replace long and continuous fibre composites in engineering applications? Wouldn't it be possible to create a more sustainable future in composite manufacturing? The vision of this research is to answer these questions. The proposed research will innovate the fabrication process for discontinuous fibre composites assisted with additive manufacturing technique. The new technology will realise an automated process capable of manipulating the discontinuous fibre orientation and preform density (volume fraction) during operation following the fibre angle distribution optimal for formability and structural properties required in the final products. It will not only reduce a number of manufacturing steps such as preforming, cutting, placing, and trimming but also minimise the waste in production.To achieve the aim, a new short fibre orientation head will be developed based on a novel 3D fibre orientation mechanism. The unique alignment mechanism and its control programme will enable high-precision localised control of in-plane and out-of-plane fibre orientations as well as fibre volume fraction. The fibre orientation head will be then placed onto a CNC platform to fully automate production of 3D tailored preforms directly from the raw short fibres. The process validation will be performed by assessing the 3D microstructure of the produced preforms via CT scanning. Then the research will quantify the benefit of the 3D structured short fibre preforms and their composites for improving mechanical and structural properties.