Composites are materials that are composed of at least two or more macroscopically identifiable constituent materials. The individual constituents differ distinctively in physical or chemical properties and give the composite unique properties when combined. What distinguishes composites from mixtures and solid solutions is that the individual materials do not dissolve into each other and remain separate within the finished structure.
A composite always contains at least one material serving as reinforcement and one material serving as matrix (also referred to as binder). Often, the reinforcement phase is made of fibers and conveys desired mechanical properties. The matrix phase encloses the reinforcement, shields it from environmental influences, keeps it in place and helps to distribute loads evenly over the structure.
When designing composites, the specific phases are combined in such a way to exploit their favourable properties to the maximum while compensating for their individual downsides. Like this, it is possible to engineer materials whose properties exactly meet the demands of a specific application.
Composites have already been used in ancient years. Early composites are for example mud bricks or concrete. Modern examples of composites are often more sophisticated.
Different types of composites
Commonly, composites are categorised either according to the matrix or reinforcement material.
When focusing only on the matrix, this leads to three main groups of composites:
Considering, however, the reinforcement, one distinguishes according to the following three categories:
- Particle-reinforced Composites: In particulate composites, particles like powders or flakes are incorporated in a matrix. Concrete, for instance, belongs to this material group.
- Fiber-reinforced Composites: In fiber-reinforced composites, fibers most commonly made of glass, basalt or carbon are enclosed in a matrix.
- Laminar Composites: In Laminar composites, layers of materials are embedded in a matrix. The most common example for this composite class is sandwich structures.