Researchers at ETH Zurich in Switzerland are developing the composite materials of the future by optimising the core elements of sandwich structures.

The researchers say this will enable them to create materials that are incredibly light, robust and adaptable, and therefore ideal for aerospace applications.

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Paolo Ermann, professor for Composite Materials and Adaptive Structures at ETH, says: “It is our philosophy to develop modern composite materials for adaptive systems and, while doing so, to optimise their structural efficiency – that is, obtaining the same performance with fewer resources or better functionality with the same amount of material.”

Sandwich structures typically consist of two thin, stiff cover layers and a low-density core material. “In our research, we develop high-performance sandwich composites made of carbon fibre-reinforced polymers, also known as CRP’s or simply carbon fibre. In this approach, the core consists of a truss structure of carbon fibre rods”, says Christoph Karl, a PhD student working on the project.

The mechanical properties of carbon fibre mean that these core structures can have greater stiffness and stability than conventional foam or honeycomb cores.

According to Karl, another significant advantage of the truss cores is the load-optimised design capability. He explains: “The mechanical properties of the sandwich composite depend strongly on the core topology – in other words, on the arrangement and orientation of the rods inside the core. With the help of numerical optimisations, we can tailor the orientation of the rods to specific external loads and thus maximise the structural efficiency for a particular application.”

Applications in aerospace

The core of a sandwich material constructed and optimised in this way weighs less than 30 kg per cubic metre (a cubic metre of steel weighs in at around 8,000 kg).

“This makes our materials particularly interesting for aerospace applications, where structural efficiency is of crucial importance,” says Karl. “Moreover, it is possible to integrate additional features, such as vibration damping, directly into the core structure.”

The team is investigating applications of the new sandwich structures through the EU project ALTAIR, led by the French aerospace lab Onera. Ermanni’s research group is involved in the development of load-bearing structures of new deployment systems for small satellites.

Towards 4D printing

Spin-off company 9T Labs, co-founded by Ermanni’s PhD student Martin Eichenhofer, is also developing a 3D-printing technology that can be used to produce high-quality carbon fibre components, such as the rods for sandwich structure cores.

“First and foremost, this is about expanding the range of application of such materials through novel production techniques, which will enable smaller companies to use them as well. This democratises lightweight construction technologies, as it were,” says Eichenhofer.

“This procedure also opens up the possibility of integrating active elements directly into the printing process in the future, thus realising 4D-printing,” Ermanni adds.

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