Andrew Doyle/LONDON
THE UK DEFENCE Evaluation and Research Agency (DERA) claims to have produced the world's first continuous, hollow carbon fibre, from a polyacrylonitrile precursor. Hollow fibres have the potential to improve significantly the compressive properties of composite materials, says DERA, as well as providing further weight reductions compared with conventional materials.
"Micro-buckling of fibres has been identified as a critical failure process, but a relatively large-diameter hollow fibre will be much more resistant to buckling than narrower, standard fibres," says DERA. A hollow fibre could also incorporate a different material along its core, allowing composites with novel or specialist properties to be applied in areas such as stealth technology, smart systems or "self-repairing" structures.
The hollow fibre can be manufactured with an outside diameter of about 20µm, with a wall thickness of around 5µm. More development work, aimed at maximising composite compressive strength while maintaining tensile properties, is assessing the effects of varying the fibre diameter and wall thickness. Later studies will consider scaling -up fibre production to larger-scale multi-filament tows, and to the fabrication of composite components for performance evaluation.
The process has been developed by DERA's Structural Materials Centre (SMC) in conjunction with Strathclyde University, Scotland. The fibres are produced by the SMC's research-scale pilot plant at Farnborough.
Source: Flight International