This phenomenon, which makes it possible to improve the quality of the material when faced with a certain use (lightness, rigidity under stress, etc.) explains the growing use of composite materials in various industrial sectors.

We find two or more elements in the assembly of a composite material. By varying the elements, we adapt the composite material to the conditions of use.

A composite material is composed as follows: matrix + reinforcement + optionally: filler and/or additive. Examples: reinforced concrete = concrete composite + steel reinforcement, or fiberglass composite + polyester resin.

These elements can be classified into these three categories:

• Matrices : Matrices are often liquid resins but can also be solid.
• Reinforcements : Reinforcements add strength to the composite material. They are responsible for the mechanical properties of the composite material.
• Fillers and Additives : Fillers and additives will be incorporated into a composite material with a view to modifying the color, reducing the cost, improving the fire resistance, reducing shrinkage, facilitating demoulding, modifying certain thermal or electrical properties, improving the resistance to aging and modifying the density of the material. This phenomenon, which makes it possible to improve the quality of the material when faced with a certain use (lightness, rigidity under stress, etc.) explains the growing use of composite materials in various industrial sectors. Nevertheless, the fine description of composites remains complex from a mechanical point of view due to the non-homogeneity of the material.

In fact, a composite material is custom designed to the desired properties.