As fuel prices continue to rise and awareness of climate change grows, one might expect carbon fibre and other lightweight composites to be at the top of every carmaker’s R&D shopping list, but things are not so simple
Racing improves the breed – an oft-heard maxim that has been used to try and justify the cost of racing and particularly the outrageous cost of Formula 1. But Formula 1, like all businesses in these straitened times, has had to cut its budgets; talk of reducing an annual team spend from around £250 million to just £20 million by the end of 2010 has spurred talk of common engines and chassis. In 2007, the sport’s governing body, the FIA, called for “standard chassis and energy-efficient engines to drive the Formula 1 championship towards a cost-effective, road-relevant and eco-friendly era.”
This should bring the lightweight elements that make racing cars so efficient in performance terms closer to the grasp of the road-car customer, but carmakers are wedded to mainly steel and some aluminium chassis and body construction. Usage of carbon fibre (CF) is confined to consumer-visible, low production models that hint of race pedigree – carbon fibre and ‘carbon-look’ dashboards, roof panels, engine covers and keyrings… not really ‘roadrelevant’. And none of these parts really exploit the material’s extraordinary properties; high tensile strength, low weight, and low thermal expansion – all antitheses of common steel body construction.
Road car usage of the material continues to be in ‘supercars’, examples of which are the Porsche Carrera GT and Bugatti Veyron. The Veyron has an interesting CF-aluminium composite construction that may point the way forward for larger series production applications. The passenger cell of the car is comparable to the cockpit of a racing car. Designed in a monocoque construction, it is described by the makers as a ‘survival cell’ for two persons.
Just like human hair, getting its strength from many tiny parts, CF is made up of fibres about 0.005–0.010 mm in diameter, mostly composed of carbon atoms. These atoms are bonded together in microscopic crystals more or less aligned parallel to the long axis of the fibre. The crystal alignment is critical to the fi bres’ high strength. Several thousand carbon fibres are twisted together to form a yarn, which may be used by itself or woven into a fabric. Carbon fibre has many different weave patterns and can be combined with a plastic resin and wound or moulded to form composite materials such as carbon fibre reinforced plastic (often called carbon fibre) to provide a high strength-to-weight ratio material.
This may not be as fanciful as it sounds; the 16-cylinder engine produces in excess of 1000PS and the car is capable of more than 250 mph. The centre of the frame structure is formed by the carbon fibre passenger cell, which is built in exactly the same way as the survival cage of a Formula 1 car, the monocoque construction weighing approximately 110kg. The rear section of the monocoque is designed with a hollow space to hold the 98-litre saddle fuel tank which surrounds the transmission. The tank area forms part of the monocoque.
The front section of the Bugatti Veyron 16.4 is rigidly attached to the monocoque front and consists of an aluminium frame structure weighing only 34kg. This performs two essential tasks: it holds the front section components, including the front axle differential, radiator package, steering system and battery, while also taking the suspension loads. In addition to this, the front section of the car is designed as a crash structure, absorbing kinetic energy to deform in a calculable way in the event of an accident. The advantages of this structure are manifold, as Bugatti development chief Dr. Wolfgang Schreiber explains: “The torsional rigidity from axle to axle is around 60,000 Newton metres per degree, a value which is twice as high as that which is customary in modern series-built sports cars.” Mounted to the rear section of the monocoque are so-called “bags”, which serve as top longitudinal supports and also accommodate the MacPherson struts of the rear suspension. These longitudinal supports are also made of carbon fibre to make them torsionally rigid and lightweight.
A carbon fibre crossbeam screwed onto the two longitudinal supports forms the rear edge of the frame structure. The steel frame mounted beneath it as a structural element accommodates the 16-cylinder engine.
The rear periphery of the frame structure consists of aluminium components designed to form a so-called crash box. They are designed to deform in a precisely calculated manner in the event of a rear collision, to absorb as much impact energy as possible.
The doors of the car are an interesting example of integrating the structural and deformation characteristics of aluminium with the rigidity of CF. They consist of an aluminium structure with aluminium ‘cladding’ on the outside, which has an integrated impact absorption system.
This helps prevent another vehicle from penetrating the interior in the event of a side impact. The deformability of the aluminium makes it possible to deflect impact energy via front link points and so-called ‘crash claws’ in the area behind the door locks. Thus the doors also perform bracing functions as part of the entire vehicle safety structure and prevent impacts from fracturing the CF structure while improving the overall ‘crashability’ of the car.
On a slightly more real-world scale, Mercedes-Benz AMG are perhaps the best example of CF use, the material going beyond decorative to add something special on a technical level to the vehicles. A special edition of the CLK Class coupe, one of the ‘Black Series’, features some interesting uses of CF. We spoke with Florian Lottes of the company’s communications department about the series: How many units of the Mercedes CLK 63 AMG Black are planned for annual production?
“The planned number of units, 700 worldwide, was successfully achieved. The CLK 63 AMG Black Series is already completely sold out.” Are all the CF panels and components constructed and fi nished on site or is any panel production contracted out to third-party companies?
“The CF components are produced by component suppliers, developed and constructed together with AMG.”
Which method does Mercedes use to construct its CF panelling, moulding or vacuum, heat or air-cured?
“Mercedes and AMG use both construction methods.”
Are there other factors in deciding to use CF, other than the favourable strength-to-weight ratio?
“Yes, AMG offers its customers several possibilities to individualize their cars at the AMG Performance Studio, as an AMG Carbon package. AMG tries to fulfil all customer needs, while wishing to respect the Mercedes- Benz and Mercedes-AMG safety regulations, legal and guarantee requirements.”
Did the favourable climate for CF bodywork in terms of marketing affect the decision?
“With much AMG inspiration coming from the racetrack, CF bodywork is included in our Black Series cars as a product of the AMG Performance Studio, which was founded in 2006. One aspect for using CF is giving our customers even more aspects to individualize their cars, for example, with our special AMG Carbon packages.” CF is a notoriously difficult, time-intensive material to work with.
How did Mercedes solve the inherent problems associated with large-scale production of CF body panels?
“It was the Mercedes-Benz SLR McLaren, which marked the first ever use of carbon fibre technology to such a large extent in series car production. Before this, carbon fibre composite (CFRP) components were built by hand in a time-consuming process. In order to achieve a high degree of automation, the experts at the Mercedes-Benz Technology Centre in Sindelfingen, working together with Daimler Research, split the production process into two parts: pre-form production on the one hand and resin saturation with subsequent curing on the other. By drawing on the skills of the textiles industry, the materials specialists at Daimler were able to introduce largely automated production of the preform, which also consists of carbon fi bres. Furthermore, traditional production processes used in the textiles industry – such as stitching, knitting, weaving and braiding – were specifi cally adapted for the production of advanced CFRP materials.(fi rstly used for the SLR McLaren in 2003).”
What changes in CF panel production were put in place to reduce costs, if any?
“This depended on the arrangements we made with the suppliers.” Is there an economy of scale, in other words, does the production of CF get cheaper the more you make?
“The CF parts being used are quite cost intensive. Depending on the units and automation of technical processes, cost reductions can be achieved. For the exclusive 700 units of the CLK 63 AMG Black Series, our goal was to offer our customers a highly-exclusive sort of race car with immense track performance, combined with a touch of comfort.”
Will the CLK 63 AMG Black Series undergo EuroNCAP testing and how are Mercedes preparing for those tests, given the unpredictable nature of CF panels under impact?
“The CF materials being used in the CLK 63 AMG Black Series were thoroughly proved in crash tests.”
What plans does Mercedes have to incorporate CF bodywork in future models?
Of course we do not give out this type of information about future models. But I would say that CF is an exclusive material to work with and has a lot of potential. Still, it is a high-priced material that takes up time in development and production and needs a lot of professional skill to handle.
From the supercar to the super low-cost car
The Bugatti Veyron is one of the world’s most expensive cars at €1,400,000. At the other end of the price spectrum is the Tata Nano, destined to sell in India for €1,600; the budget car employs a different type of composites application in the powertrain area.
The Nano has a plastic air intake manifold, made with BASF’s Ultramid glass-fibre reinforced engineering plastic.
The component will be produced by Tata Visteon. The air intake manifolds would traditionally have been made from aluminium, but the composite part offers a 40% weight saving, in turn leading to better fuel efficiency and lower emissions, essential features for the Nano with its modest power output. BASF took the lead on this project, providing more development support than would usually come from a materials supplier; ranging from computer simulation studies in the design phase to component tests in the trial phase, carried out at the company’s engineering plastics technical centres.
Kevlar is an ‘aramid’ fibre, meaning its chemical composition is poly para-phenyleneterephthalamide, more commonly known as a paraaramid.
Aramids belong to the family of nylons. Common nylons often do not have optimal structural properties, so the para-aramid distinction is vital. Kevlar is supplied as a continuous filament yarn, cut fibre that can be converted into yarn or thread, sheets and fi brillated pulp.
In different forms it is used in a myriad of applications, from bullet resistant vests to underwater cables, parachutes, space vehicles - and now tyres.
Round and black – and a lot more
At this year’s International Geneva Motor Show, the tyre division of Dunlop unveiled a look into the possible future of tyre technology: an ultra-lightweight concept tyre, with the latest DuPont Kevlar technology replacing some traditional steel components. By using this technology, Dunlop says it is aiming for a combination of better fuel economy, combined with excellent performance characteristics and improved handling feel and ride quality.
Steel is normally used in several tyre components, in the form of very fine wires wound into flexible, strong cords. These steel cords are used in the tyre’s breaker or tread area, and also in the beads. “Steel has been an effective material for many years,” says Bernd Loewenhaupt, Dunlop Director of Consumer Tyre Technology. “However, since steel is relatively heavy, our continued research and development efforts focus on strong but lighter materials to reduce fuel consumption without compromising on the tyre’s endurance. We are working closely with the R&D teams of DuPont to further employ their Kevlar fibre for our future high performance tyres,”
Kevlar is a synthetic fibre five times stronger than steel on an equal weight basis, further capable of maintaining its strength and resilience in a wide range of temperatures, and it has been used to replace almost all the tyre’s steel elements.
For some steel components, the Dunlop engineers used special hybrid materials and other forms of nylon to reduce the tyre’s weight.
The tyre on display, which is an ongoing research and development project of the company’s development centre in Hanau, Germany, is 25% lighter than comparable tyres of the same size. “Such an enormous weight reduction would lead to significantly lower levels of rolling resistance and fuel consumption”, explains Loewenhaupt.
Pininfarina’s electric car concept, the ‘Pininfarina BlueCar’ was equipped with the concept tyre, with the design house styling the tyre’s tread and sidewall to suit the concept car.
Kevlar has already been used in Dunlop’s SP Sport Maxx TT tyre in the form of a pulp, consisting of highly-fibrillated chopped fibres that are used as special additives to enhance performance by providing improved reinforcement and viscosity control under stress. The tyre features Kevlar EE in the apex compound for a stiffer sidewall, which provides more resistance to torsion, tension and heat. This leads to increased stability during cornering, as well as enhanced road feedback. The apex is part of the tyre’s sidewall and located radially outward from the tyre’s bead.
Composite is a wide-reaching term, encompassing glassfibre, polyamides and many polymer-based mixtures.
The classic problems of replacing structural metal parts with composites have been addressed by laminating metal beams into ‘plastic’ skins, and incorporating carbon fibre, Kevlar and other exotic substrates to replace the ‘lost’ rigidity of the full metal construction. Now a joint project between a chemicals supplier Rhodia and component maker Inoplast has broken new ground by creating the first polyamide reinforcement beam for truck radiator grilles. This project, which has gone into production on a well-known range of trucks (still unrevealed as we went to press), is aimed at reducing costs and overall vehicle weight without interfering with the function of this key structural element. Rhodia’s newgeneration polyamide, Technyl Star AFX, proved to be the only material able to meet project specifications, thanks to its mechanical strength, combined with its high levels of fluidity.
The use of this polyamide resulted in a cost saving of 30% compared with an equivalent metal beam, as well as a reduction of over 10% in the part’s weight, contributing to a lighter vehicle and consequently to a reduction in CO2 emissions.
The material outperforms standard polyamide, due to its high rigidity, coupled with a good surface appearance, regardless of its high glass fibre content (up to 60%). The fluidity of the material also aids injection processing, while achieving a previously impossible degree of rigidity for polyamide.
In addition to its product, Rhodia has further contributed its next-generation simulation tool, able to more accurately predict the behaviour of polyamide parts by taking glass fibre orientation into consideration in structural calculations. This enabled Inoplast to more precisely define the ideal part design needed to meet rigidity and vibratory control requirements for the beam, while optimizing its weight.
Aside from the slow uptake of composites in the automotive industry, a major concern is the sustainability of materials and the effect they have on the recycling chain. In short, the very qualities that make them attractive, their toughness and durability, mean they do not in most cases break down easily into recyclable elements and of course, unlike steel, they cannot be simply melted down.
At the recent JEC exhibition and conference, AMS spoke with Dr. Elmar Witten, Managing Director of the AVK, the German Federation of Reinforced Plastics, and asked him about the meeting of the new working group on sustainability that took place on 30 March, 2009.
AMS: How did the AVK working group on “sustainability” come about and what are its aims?
Dr. Elmar Witten: The considerable interest of AVK member companies in this topic reveals its impact on today’s composites market. There were more than 30 participants at the meeting, representing the entire value chain of composites; the list included raw materials producers, processors of reinforced plastics, mechanical engineering companies, and institutes and inspection authorities, they were all actively contributing. All of them are interested in speaking a common language with regard to the comprehensive assessment of the ecological, economical, and social effects of the materials throughout their entire lifecycle.
AMS: What is the German composites industry’s position today with regard to “sustainability”? What is the AVK members’ opinion with regard to this topic?
EW: Initial attempts have been made to perform lifecycle and ecoeffi ciency analyses, especially by major companies throughout the chemical industry. The considerable importance of this topic has been acknowledged; albeit not by all companies, and especially not by some of the small and medium-sized plastics processors.
AMS: How would you identify the challenges in your sector of industry that are getting in the way of increased sustainability?
EW: Our success depends partially on encouraging all market players to contribute to the implementation of corresponding projects. On the one hand, a pragmatic start should be made now. On the other hand, continued efforts are needed to develop appropriate methods and concepts.
AMS: Communication regarding sustainability between all stakeholders involved in the creation of value is important, both on a national as well as a European scale. How is AVK going to ensure that all partners are fully informed and involved?
EW: AVK will communicate the results of the regular working group meetings to all AVK members, not only to the working group members; members of other European composites federations, too, are invited to participate in this network. AVK is to use the EuCIA to distribute the information throughout Europe.
