Composite materials: just carbon fiber or much more?

We answer the question now to remove one doubt. It can, in fact, mislead, as it is incorrectly posed. When we talk about composite materials, in fact, we are not only referring to those containing carbon fibre, but this world is much wider. Furthermore, we do not speak of “carbon fibre”, but of “carbon fibre-based composite materials”. The latter does not represent the entire composite material, but only one of the two parts necessary for its creation.

Let’s go into the order, starting from the beginning and analysing specifically the world of composites. These materials are defined as follows:

Composite material –> Multiphase material, artificially created by combining two or more components, or phases, in which the latter are distinguishable by the presence of a clear interface, so that the final product has properties different from those of the constituents.

Carbon fibre composite materials sem
Observation of a composite material under a scanning electron microscope (SEM): it is possible to observe the reinforcement, in fibre form, immersed in the matrix.

Constituents of a composite material

In a composite they can be distinguished:

  • Matrix: represents the continuous phase and, depending on the type, allows applications of the composite at different operating temperatures:
    • polymeric –> operating temperatures lower than about 250°C;
    • metallic –> operating temperatures lower than about 1000°C;
    • ceramic –> operating temperatures above about 1000°C;
  • Reinforcement: which represents the dispersed phase and may be of a different nature, depending on the matrix used and the properties of the composite to be obtained:
    • reinforcement in the form of fibers –> e.g. carbon fibers, but also glass fibers, polyamide fibers (nylon), polyaramide fibers (kevlar), polymer fibers of various kinds, etc.. The fibers, in turn, can be distinguished into long fibers, which allow to obtain better mechanical-structural properties, or into short fibers, which limit the resistance properties, but are now much in demand, especially in Middle Eastern countries, for their aesthetic effect (“marble effect”);
    • reinforcement in the form of particles of different morphology –> e.g. rigid particles (glass) or plastic particles;
  • Reinforcement/matrix interface, possibly modified with coupling agents. The latter, in fact, improve the wettability of the fibers and promote the formation of bonds at the interface, so as to optimize the adhesion matrico/support;
  • Fillers (or inert fillers), which allow to reduce the matrix content, and also the cost of the material, in addition to implementing dimensional stability.

The importance of reinforcement

The reinforcement must have particular characteristics to be defined as such, such as greater rigidity than the matrix, optimal size and morphology, stability and, possibly, a cost not too high.

Applications of composite materials

The world of composite materials, therefore, unlike popular knowledge, is very wide and ranges in several areas, not only focusing on carbon fiber materials. Applications range from the aerospace sector, to then move on from the automotive/sports sector to the naval sector, up to applications, considered less noble, on which often the reasoning does not even focus. It is no coincidence that reinforced concrete itself, used every day in building construction, is itself a composite material.

This is a brief introduction to the world of these high-performance materials, but also very sophisticated and rich in technology and know-how. In the next articles will be proposed, in more detail, different classes of composites, analyzing their production process and their applications. We will also provide the opportunity to create such artifacts, directly at home, and thus be able to take some small satisfactions!

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