Fibre-reinforced plastics increasingly play a key role in mitigating the effects of crashes in automotive and other transport applications. Compared with steel and aluminium, composites based on carbon fibres (CFRP) and glass fibres (GFRP) exhibit higher impact energy absorption efficiency, resulting from a controlled fracture mechanism instead of classical plastic deformation of metal. This makes it possible to achieve a higher safety level with significantly lower mass of structural components, which supports the development of lightweight solutions.
These technologies have been validated in motorsport and are now increasingly used in series production of safety-critical components such as crash boxes, B-pillars and battery housings. Lightweight designs based on composites are applied wherever simultaneous mass reduction, improved passive safety and high stiffness and structural integrity are required.
"Lightweight construction is an important principle for saving materials and energy in the manufacture of components," emphasises Prof. Dr Markus Milwich from the Competence Centre for Polymers and Fibre Composites at the German Institutes for Textile and Fibre Research (DITF) and representative of the Lightweight Construction Alliance Baden-Württemberg. As indicated by a study commissioned by the German Federal Ministry for Economic Affairs and Energy, the lightweight construction market is developing dynamically, which is reflected in the growing number of patented solutions.
According to this analysis, the number of patents relating to plastics and plastic composites in lightweight construction applications increased by almost 400% between 2001 and 2021. "In 2019, lightweight construction generated approximately 4% of Germany's gross domestic product and provided around 3.2 million jobs," summarises Prof. Dr Markus Milwich. These figures confirm that material technologies based on plastic composites are gaining growing economic and industrial importance that goes far beyond the automotive sector.
High resistance to crash loads
The use of carbon fibre reinforced plastics in vehicles is one of the key development areas in modern mobility. This is particularly true for passive safety. Under collision conditions, CFRP composites achieve specific energy absorption of up to around 100 kJ/kg, which is significantly higher than the typical 20–30 kJ/kg for steel. Instead of the abrupt yielding and folding characteristic of metallic structures, the composite structure undergoes controlled failure, dissipating impact energy in a more predictable manner and over a longer time span.
Gradual force absorption enables the development of structural solutions with an increased safety level for occupants. An example is hybrid sandwich structures with a plastic core and outer layers of fibre-reinforced material. Such a system provides a favourable combination of low mass, stiffness and controlled energy absorption capability in crush zones. As a result, it is possible to design components with optimised deformation characteristics in frontal and side impacts.
Reducing crash energy by lowering mass
Vehicle mass is a key parameter influencing crash energy. CFRP materials can be up to 50% lighter than steel. Mass reduction leads to a decrease in kinetic energy in collision situations, which may translate into lower loads on the vehicle structure and on occupants. Properly designed composite systems thus make it possible to simultaneously reduce mass and improve passive safety characteristics.
Research and development on lightweight structures also covers the field of electromobility. The Fraunhofer Institute for Structural Durability and System Reliability LBF has developed a three-dimensional sandwich battery housing made of fibre-reinforced plastic. According to the data presented, it is approximately 40% lighter than a comparable aluminium housing. At the same time, it integrates flame retardant functions and meets the requirements of the ISO 12405-2/-3 safety standard, which provides a high level of protection for energy storage systems in electric vehicles while reducing total system weight.
Impact of lightweight design on energy consumption
Reducing component mass affects not only crash behaviour but also operational efficiency. "Especially for moving masses such as cars, aircraft and ships, every gram of weight saved over the entire service life of the vehicle results in fuel savings," explains Prof. Dr Markus Milwich. According to data from the U.S. Department of Energy, a 10% reduction in vehicle weight can reduce energy consumption by up to 8%. This indicates a direct link between lightweight design and energy efficiency in transport.
Fibre-reinforced plastics play a dual role in this context. On the one hand, they enable mass reduction thanks to their high strength-to-density ratio; on the other, they allow passive safety levels to be maintained or improved through high impact energy absorption capability. In many applications, this makes it possible to achieve a compromise between structural, operational and safety requirements without the need for additional mass-intensive protective measures.
Development directions and sustainability aspects
The growing importance of lightweight construction means that increasing attention is being paid to sustainability and recyclability of materials. One of the development paths involves thermoplastic matrix systems based on PET, which combine recyclability with mechanical properties provided by carbon fibres[6]. These solutions aim to reduce the environmental impact of composites while maintaining high stability and durability of structures.
The introduction of recyclable polymer matrices into structural composites may, in the longer term, contribute to improved material balances in the transport sector. The use of such materials in bodies-in-white, structural elements and housings of energy storage systems represents a step towards linking lightweight design concepts with the principles of the circular economy.
Plastics therefore form an integral part of lightweight, high-performance structures in future mobility. As Prof. Dr Markus Milwich points out, thanks to their high energy and resource efficiency, lightweight construction is closely linked to climate protection, sustainability and resource conservation. Combined with progress in composite processing and recycling, fibre-reinforced plastics can play an increasingly important role both in the design of vehicle safety systems and in shaping the overall environmental footprint of transport systems.
