Green light for recyclable aircraft structures TU Braunschweig works on sustainable aviation at its Stade institute site

Fibre-reinforced plastics play a central role in modern aircraft construction: they are lightweight, extremely resilient and resistant to material fatigue. Until now, however, it has been difficult to reuse these high-performance materials after they have been used. Although some are recycled, it has not been possible to use the resulting materials for safety-relevant applications such as aircraft construction. The interdisciplinary project reFrame, initiated by Leibniz Universität Hannover, Technische Universität Braunschweig, Clausthal University of Technology and Göttingen University of Applied Sciences and Arts, aims to change this. The aim is to optimise the recycling of carbon fibre-reinforced plastics so that the recycled materials can be reused in aircraft construction.

This ambitious project is being funded with a total of €4.7 million from the European Regional Development Fund (ERDF) and the state of Niedersachsen, of which €1.15 million will go to TU Braunschweig. Over the next three years, the Institute for Aircraft Design and Lightweight Structures (IFL) will conduct top-level research into sustainable aviation.

Particular attention will be paid to sandwich construction, a special form of composite material. This construction method, which consists of two skin layers and an intermediate core material, offers a promising alternative to conventional fibre composite structures in aircraft construction due to its excellent lightweight potential. However, the materials used have not yet been able to be reused in equivalent structural components at the end of their service life.

The aim of reFrame

The aim of reFrame is to enable a closed-loop recycling of carbon fibres while retaining the high performance potential of carbon fibres. The background to this is that no loss of performance can be accepted in such high performance components, otherwise the structural weight and thus the fuel consumption of aircraft, for example, would increase.

The reFrame project is developing, analysing and implementing the idea of combining CFRP sandwich structures with a core made from recycled thermoplastic cover layers. As the cover layer and the core are the same starting material, the entire structure can be recycled and processed into a new core. This creates a closed-loop CFRP sandwich recycling system with no restrictions on use.

Professor Sebastian Heimbs, Head of the Chair of Aircraft Design at the IFL: “We are delighted to have been awarded the contract for the reFrame project. This is an important milestone on the long road to zero-emission air transport. In addition to all aspects of emission reduction and alternative propulsion systems, the focus here is on reducing grey energy, i.e. manufacturing energy, through the reusability of carbon fibre structures. This is an ideal complement to our other research areas for sustainable aviation.”

The project will conclude with the realisation of a demonstrator of a recycled aircraft structure. The knowledge gained from this will be used in the transfer part with the help of the Private University of Applied Sciences Göttingen (PFH) to work directly with industrial partners on further implementation.

Stade – a location with advantages

Thanks to the interdisciplinary research cooperation in the inter-university research network HP CFK (Leibniz Universität Hannover, TU Clausthal and TU Braunschweig) at the Stade location, the entire development process can be covered: from overall design and layout (TU Braunschweig) to material analysis and recycling (TU Clausthal) to production (Leibniz Universität Hannover). The cooperation is supported by the Private Fachhochschule Göttingen (PFH), Hansecampus Stade, which is actively involved in knowledge and technology transfer.

The research alliance is based at the CFK Nord research centre, making use of the site’s optimal facilities, networking and transfer opportunities. Since 2011, this constellation has been researching innovative composite aircraft structures and their production.

As part of the reFrame project, three new research assistant positions will be created for three years at the Institute of Aircraft Design and Lightweight Construction at TU Braunschweig in Stade, and a further six positions will be created at the direct project partners in the HP CFRP research network. The funding is therefore an important part of the TU Braunschweig location and a significant contribution to regional development.

“The interdisciplinary research environment in Stade gives us insights into the entire development process and offers many opportunities for collaboration at key interfaces. I am very much looking forward to working with my colleagues and our partners here at the IFL to make tomorrow’s mobility more sustainable,” says M.Sc. John Finder, research associate at the IFL.

Both chairs of the Institute of Aircraft Design and Lightweight Construction involved

The Chair of Overall Aircraft Design will analyse possible applications – adapted to the use of recycled structures and future mobility requirements – and create an aircraft design. In addition, the Chair of Aircraft Design will design the structure using methods adapted to recyclates (reused, recycled raw materials), as recyclates have a higher variance in their material properties.

The potential for lightweight construction can be increased through targeted functional integration, such as the introduction of fire hammers or sensors for structural monitoring. In order to enable the complete and unmixed recycling of structures, the research project focuses in particular on reversible joining methods.

As a measure to strengthen the regional knowledge transfer in a sustainable way, both a pronounced transfer phase in the advanced course of the project and continuous transfer work by the PFH are planned. In particular, in cooperation with interested SMEs, potential topics will be identified and evaluated in the context of preliminary studies accompanying the project, which are closely related to the application-related questions of the participating industrial partners and which aim to transfer the project results obtained into follow-up projects in the companies.