Reshaping ceramics with 4D printing
A printable ceramic ink has been created that can be origami folded to create complex structures, such as the Sydney Opera House. Ceri Jones reports on the applications of this hybrid ink.
Shape-shifting structures could open up new possibilities in construction and design, following the development of a ceramic-polymer fluid for additive manufacturing. A research team at the City University of Hong Kong reported that after two-and-a-half years they have developed two types of polymer-derived ceramics (PDCs) that can undergo self-shaping when subjected to a range of stimuli, such as changes in temperature, light and electromagnetic fields. Augmented PDCs retain the same characteristics as normal ceramics – having chemical and corrosion resistance, thermal stability and being non-oxidising – but treatments such as thermolysis can trigger specialised behaviours.
While it is already possible for ceramic material to be 3D-printed, this is difficult due to its high melting point and tendency to make inflexible precursors and, therefore, basic shapes. In contrast, the team’s silicone rubber matrix nanocomposites (NCs) enable them to 3D-print soft elastomer precursors that can be manipulated and deformed, adding the extra dimension of time – a delay period where the forms can be moulded and self-assembled before firing, when they solidify in the same way as any other ceramic matter.
The research team, led by Professor Jian Lu, Vice-President Research and Technology, and Chair Professor of Mechanical Engineering at the university, published the paper titled Origami and 4D printing of elastomer-derived ceramic structures in Science Advances journal.
Lu points out that, from vast aerospace and transport components to electronic devices, foldable elastomer-ceramics can deliver benefits wherever robust, thermally resistant parts are required. ‘Ceramic materials have much better performance in transmitting electromagnetic signals than metallic materials. With the arrival of 5G networks, ceramic products will play a more important role in the manufacture of electronic products,’ he said. ‘Since ceramic is a mechanically robust material that can tolerate high temperatures,’ he added, ‘the 4D-printed ceramic has high potential to be used as a propulsion component in the aerospace field.’
Feeling the strain
According to the authors, the key ingredient enabling this breakthrough is the nanocomposite material – zirconium dioxide nanoparticle (ZrO2 NP)-reinforced poly(dimethylsiloxane), or PDMS for short, which provides the necessary flexibility for deforming. The PDMS formula produces an elastomeric precursor that can be stretched more than three times its original length.
Testing involved creating two different elastomer ink formulae – ZrO2 NPs at 20% weight and 40% weight – and putting them through various construction methods. Firstly, a substrate base was 3D-printed and stretched, then a 3D-printed precursor with a Miura-ori pattern, similar to a topological map, was joined to the base and the strain released. The subsequent buckling and folding was controlled by the precursor’s printed design, causing the material to shape itself in to the mountainous folds.
It was also possible to insert iron wires into joints to manually fold the elastomer, in the manner of origami. Once fired, this process produced intricate structures including the Sydney Opera House
and a rose. Method two involved direct ink writing on to pre-stretched precursors. As the pattern dictated the joints, once released, the formers morphed into the desired shapes, including helical twists and saddles.
This research has identified two proven and scalable methods of 4D printing elastomer-ceramics, and mechanical testing of 3D-printed honeycomb and microlattices confirmed high compressive strengths of 547MPa on the microlattice at 1.6g/cm3. Thus far, Lu has claimed that the 4D printing processes are more time and cost efficient, due to the ability to craft stable, intricate shapes without the need for costly equipment, such as lasers, commonly used with other methods. Going forward, the team is working on improving the elastomer-ceramic ink
to reduce its brittleness.