Researchers investigate effects of lightning strikes on aircraft

Scientists in the UK are researching the potential for damage posed by lightning for carbon fibre composites (CFCs), which are increasingly being used in aircraft manufacture, with a view to reducing damage and minimizing repair costs.

Dr Igor Golosnoy, of the University's Electrical Power Engineering Research Group within the School of Electronics and Computer Science (ECS), is working with EADS Innovation Works UK on a three-year project which aims to assess the effect of lightning strike on modern CFCs materials used in airframes or wind turbine blades.

Aircraft manufacturers are increasing the use of CFCs because they are lighter than aluminium and provide significant weight savings.

But according to Dr Golosnoy, CFCs have a significant drawback because of their peculiar structure. They contain several layers of long carbon fibres impregnated in epoxy resin and bonded together. The fibres are laid in different directions in each layer, making the composites highly electrically and thermally anisotropic (which means they have different physical properties in different directions). As a result, any lightning strike damage would present differently in each layer, making it more difficult to repair composites.

"We're not talking about any immediate danger," says Dr Golosnoy. "Modern jets can still fly safely despite lightning strike damage. The problem here is that any damage should not remain undetected and must be repaired promptly. Our role is to establish in detail how the damage occurs in composite structures and to give suggestions on repair and protection as well as to look at possible improvements in CFCs themselves.

"Although CFCs are strong and provide a superior mechanical performance, their electric and thermal conductivities are much lower than those of aluminium alloys. As a result the energy from the strike does not dissipate quickly enough along the unprotected surface, making them more susceptible to damage," he continues.

"There are several ways to protect the composites, such as having a layer of metal mesh or thin foil on the top, but this increases the overall weight and means that both the coating and the composite get damaged. It also makes the repair procedure even more complicated."

Over the lifetime of the project, which will look mainly at the fundamental physics of the phenomenon, Dr Golosnoy plans to develop a qualitative mathematical model and predict the airframe behaviour during lightning strike. He will also undertake a parametric analysis of how the layup of composites affects their thermo-electric performance.