In the line of fibre

If you can specify the development of human societies by the materials they use —stone age, bronze age, iron age and so on — then there’s a good argument for saying that we’re currently in the composite age. The lightness, strength and toughness of composite materials, bringing together the properties of a polymer matrix surrounding a reinforcing web of mineral fibres, and allowing a wide range of component shapes to be produced easily and quickly, has proved to be a godsend to engineers in many sectors, particularly aerospace.

But there’s a downside to every advantage. Most of the manufacturing sectors that use composites originally used metals, and composites behave very differently from metals. of particular interest to engineers, they break in different ways.

The journey to understanding how metal components fail in aerospace was painful - the catastrophic failure of the original design of the De Havilland Comet airliner in the 1950s showed how little was understood about metal fatigue. However, it is now well understood. But metals, with their crystalline structure and lattice atomic arrangement, are very different from composites, with their layers of oriented fibres, mass of relatively disordered polymeric chains, and the different types of atomic bonds in their various components. ‘There are many processes involved with composite failure at a micromechanical level, and they are all very complex; it’s difficult to understand them completely,’ explained Silvestre Pinho, a senior lecturer at London’s Imperial College, who is leading a project, co-funded by Airbus and Dassault Systèmes along with the EPSRC, to look at composite failure.