Carbon-fibre reinforced plastic (CFRP), a strong and light fibre-reinforced polymer, offers distinct structural and weight advantages in the automotive segment. Once used exclusively in motorsport, the material has trickled down to on-road, low-volume luxury sports cars, and onto higher volume models – albeit still in the premium segment.
Carbon fibre has really come into its own since the enforcement of stricter emissions standards, which brought about the need for better fuel efficiency. What this translates into is the need for lighter vehicles. Replacing steel with CFRP has the potential to significantly reduce vehicle weight by up to 60%. Weight savings in this range would transform into an increase in fuel efficiency to the tune of around 30%, and of course, this in turn would cut emissions by up to 20%.
“The penetration of carbon fibre depends on several factors, such as the development of emobility and the strictness of emission regulations. With introduction of WLTP [Worldwide harmonized Light vehicles Test Procedure], weight becomes increasingly more important. In mature markets it seems realistic that within the next decade carbon fibre becomes, for premium OEMs, an attractive option, but mostly in larger, high-priced vehicle segments and mainly as part of ‘hybrid’ body structures,” said Dr Wolfgang Bernhart, Senior Partner at Roland Berger.
Although the material has a high potential for vehicle weight reduction, costs are still very high at present. This is, however, expected to drop quite significantly over the next couple of decades, bringing the material into better competition with other lightweighting materials, such as aluminium.
“From its technical material performance level, carbon fibre has a great potential for substituting steel or aluminium. However, current and mid-future manufacturing technologies will not be able to meet mass market cost levels,” Dr Bernhart continued.
Production advantages
Owing to the cost factor, CFRP is, at present, predominantly used in low-volume, luxury cars, and mainly for prominent sections, such as roofs, interiors and decorative parts. The next step will be entire vehicle modules, as BMW has shown with its significant use of CFRP on the electric i3 – the first use of the material for large series production in the automotive industry.
“The body structure of the BMW i3 is completely made of this extremely lightweight and durable material, compensating for the additional weight of the battery for the electric drive,” said Dr Rüdiger Bräuning, Technology Validation Manager, responsible for CFRP Production Technology Development at BMW Group.
According to SGL Automotive Carbon Fibers, a joint venture between SGL Group and BMW Group, one of the advantages using this material is that different functional parts, such as fasteners and supports, can be integrated into the component. Even complex structural parts, or entire body assemblies, can be produced on one machine tool, translating into a significant reduction in the number of individual components required to produce the vehicle body.
“A CFRP component can assume the function of several metal components and therefore represent a better choice when summing up its properties. Through integral construction processes enabled by this material, the number of parts can be reduced, which is usually rewarded with a cost reduction across the entire production chain,” said Dr Lars Herbeck, Managing Director of Voith Composites, the competency centre for carbon fibre products within the Voith Group.
Then there is the aforementioned weight advantage. CFRP is around 50% lighter than steel, and 30% lighter than aluminium. In addition, the material is stable, rigid and resistant to corrosion and aging. Another clear advantage is the reduction in effort that would otherwise be required to produce highly integrated and extensive body components, compared with production of the same using steel or aluminium.
“Different functions like attachments and carriers can be integrated into the component. Even complex structural parts or whole body assembly units can be made from one tool. This allows a massive reduction of individual components in body construction,” Bräuning noted.
“In the longer term…composites offer very exciting opportunities for weight reduction that will inevitably start to replace steel and aluminium,” Prodrive Composites’ Managing Director, Dominic Cartwright commented. ”At first in body panels, and then in the structure of the chassis and wider applications. The weight reduction goal is so pressing that this transition is inevitable.”
Paying the price
The elephant still sat in the room, however, is cost. At present, the price of carbon fibre components is much higher than high-strength steel and aluminium. There are also other issues, such as manufacturing cost, recycling and supply – or lack thereof. “This is the reason why carbon fibre will not be immediately be adopted by the automotive sector in mainstream vehicle manufacturing, but more likely in three to five years’ time,” said Leonidas Dokos, Research Director of Chemicals, Materials and Food at Frost & Sullivan.
There is also the matter of maintenance and repair of components and parts made using CFRP. According to a study conducted by McKinsey & Company, often damage to such components cannot be determined through a visual inspection, requiring acoustic emission detection, or thermal, ultrasonic or X-ray imaging – all of which involve potential investment costs for dealerships.
Post-crash repairs present another problem: lack of sufficient knowledge and understanding of damage diagnosis and remedial requirements for carbon fibre. As Andrew Hooker, Future Vehicle Engineer, Thatcham Research puts it, carbon fibre “is not one wonder material, and to say a car is made of carbon fibre is akin to saying its made of metal. For a repairing workshop to have the knowledge and materials to repair all will be unlikely.”
Positives and negatives aside, the shift of CFRP from luxury vehicles to higher volume cars has begun, and will gather momentum in the future as the cost of carbon fibre composites drop further. For the present time, however, use of this material is likely to be confined to higher end cars.
“We might also see some carbon fibre in premium volume cars until the middle of the next decade. As the cost level for budget cars or within emerging markets is very low, it is rather unlikely that carbon fibre will penetrate those segments or regions within the next 15 years,” said Bernhart.
