Morphing metals

Materials World magazine
,
1 Nov 2006

Lugging your laptop onto public transport could be made easier by new metallic shape-changing structures that offer the potential for roll-up laptops and keyboards.

Dr Keith Seffen of the Department of Engineering at the University of Cambridge, UK, and his team have developed structures that can be configured into at least two different and stable forms without the need for additional parts, such as hinges or locks, or sophisticated manufacturing.

Seffen says, ‘There is an absence of fundamental practical solutions that demonstrate morphing capabilities. Morphing structures are a hotbed of research within the lightweight (mainly aerospace) structures community, especially in the USA. The aim is to impart extra functionality without additional parts and complexity.’

He adds, ‘A morphing aircraft wing could have radically different aerodynamic profiles. Current "swing-wing" aircrafts rely on a large hinge to provide this function, but it is heavy and intrusive.’

The new shape-changing process is based on a flat sheet of beryllium copper alloy. Stress within it is manipulated using forming tools to bend, coil or twist the material. Seffen explains, ‘Global changes in shape produce stresses, which in turn affect localised changes that mitigate stresses – there is a hardening-softening response in the elastic behaviour during deformation. ‘For example, bend an ordinary tape measure. It is stiff until it snaps elastically, thereafter, bending of the localised crease that forms is a much softer response, which can incur large changes in shape and the tape can be coiled up. Our structures exhibit the same features except our softening phase is unstable and there exists a further hardening response – this allows a secondary equilibrium position to be obtained. But we have also created tri-stable structures, which produce this behaviour over again giving way to a third shape.’

Theoretically any metal sheet could be used, provided it can withstand these large strains. The prototypes have been tested several hundred times and there has been no affect on the structural integrity of the material, due to its resilience to the morphing process which is entirely elastic and below yield stress.

‘Our forming process creates a profiled structure from the flat sheet that is approximately 100 times stiffer than the sheet itself,’ adds Seffen.

The next step is to mechanise the manufacturing process and develop more sophisticated modelling and finite element analysis. The team at Cambridge is currently seeking commercial partners for future development, including electronics companies for applying the material as a substrate in thin electronic displays. This could create a laptop screen that can be deployed flat and stiff for reading, but snaps back into a compact tube for transportation.

As the products would produced from one sheet of metal, Seffen suggests they may be quicker and cheaper to manufacture, and lighter to handle than existing devices.

Other potential applications include reconfigurable packaging and temporary shelters that may be transported compactly and snapped into position on site.