Composites: much used, but hard to understand
Composites are extremely strong and light materials because they are a combination of polymers, and glass or carbon fibers (which give the material greater strength). Composites are used in a whole range of applications: in aircraft (for example in the mechanics of the wing flaps and in fact in 40% of all of the aircraft’s components), as the base material for carbon-framed bikes, in Formula 1 racing cars (about 85% of a Formula I car is made from composite material), for the blades on wind turbines, in pressure vessels for storing gas, in prostheses, boats, electric cars – and so much more. Space flight is starting to show a growing interest in composites, too.
A composite is what is called an ‘anisotropic’ material. This means that the material’s mechanical properties are not the same in all directions. This is explained by the material’s complex composition. And it is this very anisotropy that makes it difficult to predict when a part of an aircraft, car or wind turbine made from composite materials will break.
It is for this reason that simulations are made of these structures. For this to happen, data from sensors is required, showing the ‘real’ measurements in the material. In order to obtain that data and to keep track of the actual status of the components in real-time, sensors are used – usually optical fiber sensors. The disadvantage of these sensors is that they mainly measure stress along the length of the fiber. However, an overall picture of the material’s ‘health status’ can be gained by placing the fiber sensors in different directions on the composite material. But placing the sensors in exactly the right place is very time-consuming and difficult.