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Ecological and Multifunctional Composites for Application in Aircraft Interior and Secondary Structures

Periodic Reporting for period 2 - ECO-COMPASS (Ecological and Multifunctional Composites for Application in Aircraft Interior and Secondary Structures)

Reporting period: 2017-10-01 to 2019-06-30

Lightweight structures made from composite materials like carbon fibre reinforced plastics (CFRP) and glass fibre reinforced plastics (GFRP) have gained in importance for modern aircraft structures due to their excellent mechanical properties combined with relatively low weight. But all composite materials currently used in aviation have one thing in common: they are man-made and energy intensive in production. Renewable materials such as bio-based fibres and resins have been under investigation for a long time for their use in composites. Natural fibres like flax and ramie offer a low density and promising specific stiffness. Furthermore, their damping behaviour can be favourable for acoustic applications. To be used in aviation, the tensile strength, fire behaviour and the environmental influences still need improvements. Therefore, the main objective of the cooperation of the Chinese and European partners in the ECO-COMPASS project was to develop and assess multifunctional and ecological improved composites from bio-sourced and recycled materials for application in aircraft secondary structures and interior.
To achieve this goal, the project consortium has conducted an extensive experimental characterization of different natural fibres, resins and eco-composites, and analysed possible enhancements (mechanical, electro-magnetic, flammability, etc.) of these eco-composites with different techniques. Besides improving the existing knowledge about eco-composites, in order for these to be a real alternative to synthetic composites, it was also necessary to have analysis and simulation tools capable of representing accurately their performance, in order to ensure that the structures designed with them comply with the required security and functionality standards.

Natural fibres flax and ramie were used for different types of reinforcements like fabric and nonwoven. Honeycomb sandwich cores with wood fibres substituting a part of the aramid fibres were successfully tested. Substitution of bisphenol-A based epoxy resins in secondary structures by partly bio-based epoxy resins was investigated with promising results. Material protection technologies were studied to reduce environmental influence and improve fire resistance. Modelling and simulation of chosen eco-composites optimised the use of materials while the Life Cycle Assessment aimed to investigate the ecological advantages compared to synthetic state-of-the-art materials.

Based on the current results with the materials considered in ECO-COMPASS, partly bio-based epoxy resin systems have the highest potential for a successful application in aviation. Their properties approach the performance of the fully petrol-based epoxy resins used today. Another promising group of thermoset bio-based resin, furan, has not been considered in ECO-COMPASS, but needs to be mentioned here for the very good fire properties comparable to classic phenolic resins. As a conclusion, thermoset bio-based resins show high potential to be applicable in aircraft secondary structure (epoxy) and interior (furan).

Natural fibres such as ramie, flax and sisal have a high potential for weight reduction due to their low density and good damping properties. However, their long-term behaviour (ageing) and mechanical properties need to be further improved. Potential technologies are under development, e.g. CNC coating, plasma treatment and hybridization with rCF. Fire properties are still an obstacle for the use of natural fibres in the interior. While flammability and toxicity are already under control, the heat release and smoke density properties need further improvement. On the other hand, the Green Honeycomb (GHC) with small amount of natural fibre mixed with classic aramid fibre can be another technology with high potential for the introduction of bio-based materials in aviation composite structures. Its long-term stability (humidity, etc.) needs to be validated in further tests. Nevertheless, the GHC may be used for secondary and interior structures because of its good fire and mechanical properties.
The European and Chinese partners have increased the technology readiness levels (TRL) of the different approaches, concepts and technologies that were under investigation in ECO-COMPASS. In terms of eco-reinforcements, the project reached generally the TRL 3-4. An example is the hybrid combination of flax fibres with recycled carbon fibres in a hybrid nonwoven with TRL 3. Partly rosin-based epoxy resins and the Green Honeycomb sandwich core have achieved a TRL 4. Generic demonstrator parts for interior and secondary structure were manufactured.

Moreover, the project enabled a unique leverage of resources, reinforced a long-term relationship of China and Europe in aeronautics and allowed mitigation of risks in the eco-composites development and production. The project results are of mutual benefit in several areas such as technology and knowledge transfer, exchanges and evaluation of developed materials and adoption of modelling and simulation tools with specific application for biomaterials with their divergent and more complex characteristics compared to manmade filaments like carbon and glass fibres in composites.

ECO -COMPASS has contributed to achieve the EU environmental goals set in FlightPath 2050 by demonstrating that some aircraft components can include new, eco-efficient and competitive materials.
ECO-COMPASS project challenge
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ECO-COMPASS project context