What are composite materials and how are they classified?
Composite materials (or composites) are materials made of at least two different materials. These components retain their basic structure but are joined in such a way that they gain new, improved properties.
A typical distinction is made between:
- Fibre-reinforced composites: e.g. glass, aramid or carbon fibres embedded in a plastic matrix
- Layered composites: e.g. metal layers bonded with plastics
- Particle or structural composites: ceramic matrix composites, CMCs for short
The goal is always the same: high strength at low weight, durability and a tailored combination of mechanical, thermal and chemical properties.
Definition and composition of composite materials made from two or more materials
A typical composite material consists of two main components:
- Matrix: the surrounding phase, usually a plastic (e.g. epoxy, polyester or thermoplastics) or a ceramic, sometimes metallic base. It ensures dimensional stability, distributes the forces and protects the reinforcing fibres.
- Reinforcements: fibres (e.g. carbon fibres, glass fibres, aramid), particles or fabrics, responsible for mechanical strength and stiffness.
Matrix and reinforcement are combined in such a way that they complement each other in their functions: mechanically, thermally, electrically or even optically.
Differences between fibre composites and layered composites
Fibre composites usually consist of a continuous phase (matrix) with embedded fibres. These can be introduced unidirectionally, woven, knitted or in mat form.
Layered composites (laminates) consist of several material layers that are stacked and bonded. Well-known examples: CFRP sandwich panels or GRP corrugated sheets.
Both variants deliberately use anisotropic properties, that is directional dependencies in strength, ideal for components with targeted load paths.
The role of matrix and reinforcements in composite materials
The matrix largely determines the thermal, chemical and optical properties, whereas the reinforcing fibres primarily determine mechanical properties such as tensile, flexural or compressive strength.
Through deliberate choice of the base materials, their geometry and arrangement (e.g. fibre direction), composite materials can be optimised exactly for their intended application.
Which mechanical and thermal properties do composites exhibit?
High strength at low weight: specific properties of composite materials
A central characteristic is the strength-to-weight ratio, the so-called specific strength. Particularly for carbon composites, this ratio is significantly higher than for steel or aluminium.
Mechanical stability and elongation at break of different composites
- Carbon fibre reinforced plastics (CFRP): extremely high stiffness and low elongation at break.
- Glass fibre reinforced plastics (GRP): high toughness and good elongation at break.
- Aramid fibre reinforced plastics (AFRP): high impact resistance, ideal for protective applications.
Thermal properties and their significance for application fields
Depending on the matrix material, heat resistance can vary greatly:
- Thermoplastic matrices reach up to about 200 °C
- Thermosets and ceramics up to 400 °C and more
- CFRP with epoxy resin is ideal for applications in high-temperature environments
Where do composite materials find their main applications?
Use of carbon fibres and woven structures in aerospace
In aerospace, every gram and every mechanical property counts. CFRP components such as wing sections, fuselage segments and landing gear fairings are standard.
Innovative applications in automotive engineering and sports equipment
In the automotive industry, composite materials reduce the weight of body, chassis and interior components, which directly affects fuel consumption or the range of electric vehicles.
Sports equipment such as bicycles, skis, helmets or tennis rackets also benefit from the lightness and damping properties.
Composites in the construction industry and medical technology
GRP is used in construction as reinforcement in concrete, for facade elements or bridge elements. In medical technology, composites are found in prostheses, orthoses and surgical instruments.
How are composites manufactured and compounded?
Manufacturing processes for polymer-based composite materials
Depending on the application, the following processes are used:
- Hand lamination: simple and inexpensive for small series
- RTM (Resin Transfer Molding): liquid matrix is injected into a closed mould
- Pultrusion: continuous manufacture of profiles
- Filament winding: for pipes, pressure vessels etc.
- Prepreg technology: pre-impregnated fibre mats that cure under heat
Compounding and processing of ceramic composites
Ceramic matrices are usually combined with short fibres or particles and sintered at high temperatures. Applications: heat shields, brake linings or rocket nozzles.
Which advantages do composite materials offer over conventional materials?
Composite materials offer:
- Lightweight construction with high mechanical strength
- Corrosion resistance and weather resistance
- Design freedom through shaping in manufacture
- Damping behaviour against vibrations
- Lower thermal expansion
- Targeted material design for highly loaded zones
Especially compared to classical metals, they offer a range of advantages that have become indispensable in more and more industries.
How will composite materials develop in the future?
Innovative research approaches in composites
- Nano-reinforcements using carbon nanotubes or graphene
- Self-healing polymers in the matrix
- Sensor-integrated fibres for structural health monitoring
- Hybrid materials with metal/plastic transitions
Sustainability and recyclability of composite materials
A major topic is recyclability: thermoplastic matrices increasingly allow reuse, while thermoset systems are more difficult to recycle.
Research and industry are working on:
- Thermally removable resin systems
- Pure-grade separation of fibres and matrix
- Compostable natural fibres with bio-based matrix
GOBA Takeaway
Composite materials combine strength, lightness and versatility to a degree that conventional materials rarely achieve. They reduce weight, increase service life, optimise performance and enable innovative designs.
Particularly in the era of e-mobility, sustainable construction and smart devices, they have become indispensable in many industries. With new matrix systems, sustainable fibres and intelligent processing, they will deliver much more in the coming years and possibly set new standards.