High fibre

A fibre-metal laminate currently  under development could herald an era of ‘intelligent’ aircraft structures that need fewer mechanical systems, according to a UK engineering team.

Researchers at Liverpool University are combining two technologies — fibre composites and shape-memory alloys — that could lead to extremely lightweight and responsive aircraft with built-in self-diagnostics and a ‘morphing’ capability.

Prof Wesley Cantwell, from the university’s engineering department, claimed the work could represent a major breakthrough for the aerospace industry. ‘This would be the first material of its kind in the world,’ he said. ‘Up until now there has been a fair bit of work in combining fibre-composites with other metals such as aluminium, titanium and even magnesium alloys, but it has never been done with shape-memory alloys before.’

Fibre-metal laminates are hybrid structures based on thin sheets of metal alloy and layers of fibre-reinforced polymer materials. According to Cantwell, they offer superior structural properties over conventional aerospace materials, including improved impact resistance and a fatigue life up to 100 times better than aerospacegrade aluminium alloy. For this reason, a fibre-metal laminate is the main structural material in the upper fuselage of the Airbus A380.

Shape-memory alloys are made from alloys of nickel or titanium and have unique properties, meaning that they can deform upon heating, but can then still return to their original shape.

The Liverpool researchers are inserting thin plates of a shapememory alloy into composite materials. Heating wires to deform the alloy are also threaded into the material. An electrical current passed through the wires heats the alloy and deforms the fibre-metal in a controlled manner. It is hoped that this could lead to the development of highly controllable aircraft surfaces that, according to Cantwell, would herald a major advance for the industry.

‘This could mean that you will be able to remove much of the existing heavy and expensive equipment that is used to move aircraft flaps,’ he said. ‘The shape-memory alloy removes the need for these, because activating the alloy is a means of movement in itself. You just will not need heavy cumbersome hydraulics any more.’

The new material will also contain sophisticated optical-fibre sensors, which will allow the plane to analyse the wing deformation and make minute corrections to improve its aerodynamics. The team hopes to achieve a theoretical five per cent change in wing twist by the time the project ends next June.

The only impediment to the technology will be its cost, claimed Cantwell. However, he believes that the great weight reduction achieved would lead to considerable cost savings over the plane’s lifetime.

The results that emerge from the one-year EPSRC-funded project will be presented to potential partners in the aerospace industry once the technical and economic feasibility of the technology is fully understood, added Cantwell.