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.
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.
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.
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.