Seal of fortune

The high strength-to-weight ratio of composite materials has led to their increasing use in aerospace applications, but the materials still have drawbacks.

One is their susceptibility to damage. Where metals can deform plastically by denting and crumpling, which absorbs the energy of the impact and retains structural integrity, fibre-reinforced composites tend to crack and splinter.

What’s worse is that the damage can sometimes be very difficult to detect, as it tends to occur on the inside — the opposite face of the composite sheet to the impact. This is known as barely visible impact damage (BVID), because visual inspection is likely to miss it completely, making it very dangerous.

Researchers at Bristol University’s aerospace engineering department are working on a system to make it much easier to see damage to composite panels, and effect a temporary repair to keep the component functional until it can be replaced. Working with Hexcel Composites, Ian Bond and colleagues are trying to replicate biological healing mechanisms to devise a ‘bleeding composite’ material. The research could eventually lead to vehicles equipped with their own circulatory systems for repair and cooling, said Bond.