Supreme safety thanks to F1-style carbon-fibre monocoque
Muamer Hodzic July 2, 2007
Carbon fibre is a life-saving material. This was demonstrated most recently in dramatic fashion at the Canadian Grand Prix in Montreal on June 10 of this year, when one of the drivers suffered a horrific accident. Despite hurtling into a solid concrete wall at over 250 km/h, the driver survived the crash in his race car made from carbon-fibre composites virtually unscathed. Mercedes-Benz harnesses the safety benefits offered by carbon-fibre materials for the body of the new SLR McLaren Roadster, and builds its open-top super-sports car almost entirely from this exotic material as standard. Consequently, the new high-performance roadster not only serves up an exclusive open-air feast for the senses, it also offers a standard of safety that is unparalleled in this segment.
Formula One regulations have demanded that the racing cars be constructed from carbon-fibre-reinforced plastics (CFRP) for some years now. The first chassis made exclusively of carbon fibre was used by McLaren in 1981, and it was not long before all other Formula 1 vehicles on the racetrack had the same sort of chassis fitted. The cars comprise a monocoque that offers the driver a high-strength survival space, as well as crash structures to dissipate the impact energy extremely effectively and uniformly. It is primarily as a result of this that the risk of injury in high-speed accidents in this Blue Riband motorsport event has dropped significantly.
Mercedes-Benz employs the same principle and same high-tech material for the new SLR McLaren Roadster which receives its world premiere in autumn 2007. The monocoque – or, to put it another way, the passenger cell – of the new open-top super-sports car is manufactured from carbon-fibre-reinforced materials throughout. In the event of a head-on, side-on or rear-end collision, it therefore offers the occupants a very rigid and hence securely protected space. The crash structures in the front end and at the rear are likewise made from CFRP. “Naturally, it is not possible to completely transfer Formula One technology into a vehicle intended for everyday use, in which comfort criteria also need to be taken into account,” comments Dr. Rodolfo Schà¶neburg, Head of Passenger Car Safety Development at Mercedes-Benz. “For example, you cannot expect the driver of a series-production sports car to either wear a helmet or use the HANS Head And Neck Support system that is prescribed for racing cars to protect those parts of the driver’s body. However, we do capitalise on the positive properties of the high-tech materials used in Formula One to offer those travelling in the new Mercedes-Benz SLR McLaren Roadster a standard of safety that is unmatched, even in the realm of super-sports cars.”
The consistent use of carbon-fibre-reinforced plastic places the new Mercedes-Benz McLaren Roadster in a league of its own for, despite its obvious benefits, CFRP is generally only ever found in a few individual components of even premium-class cars, if at all, due to the elaborate manufacturing processes involved.
Carbon fibres offer greatest energy absorption
Mercedes-Benz and its Formula 1 partner, McLaren, have gathered many years of experience with this material that is conventionally used in the aviation and space industries. Carbon-fibre reinforced materials are characterised by their extreme rigidity and a level of energy absorption in an impact that is four to five times higher than that of steel or aluminium, which is why the CFRP body gives rise to such exemplary levels of occupant safety in the new SLR Roadster.
It is in the front structure of the SLR bodyshell that the impressive safety properties of the innovative fibre composite are particularly evident. Here, two conical carbon fibre composite elements, each approximately 620 millimetres in length and weighing just 3.4 kilograms, are enough to absorb the full energy of the crash in a defined frontal collision without exceeding tolerable deceleration values for the passengers.
In a collision, the fibres of the CFRP elements shred from front to rear, absorbing the energy of the impact with a constant rate of deceleration. Thanks to this uniform deformation behaviour and the high-strength monocoque, the energy absorption of the CFRP side members can be precisely calibrated. The engineers achieve this, for example, by creating a constantly changing cross-sectional area for the components. This fine tuning of the deceleration values results not only in predictable energy absorption behaviour but also in a weight advantage, because this design uses only as much material as is actually needed.
At the rear, two internal side members made from laminated carbon fibre and a robust cross member assume the task of energy absorption in the event of a crash. In an impact from the side, the occupants are protected by the broad, low-set multi-shell sills made from specially reinforced carbon-fibre materials, as well as two aluminium sections incorporated into each door. The sturdy shell of the SLR seats also has a protective function in a rear-end or side-on collision, designed as it is to hold the occupant firmly in position; it is likewise built from highly resilient carbon-fibre material.
The new A-pillar, with its additional internal reinforcement in the form of a high-strength steel tube, also contributes to the excellent occupant safety. The arrival of the Mercedes-Benz SLR McLaren Roadster thereby marks the series-production debut of a highly complex steel/carbon-fibre compound that combines high strength with elasticity. Fixed rollover bars behind the seats complement the safety concept: they ensure the passengers are afforded an outstanding level of protection even if the vehicle should turn over. Adaptive airbags, kneebags and sidebags as well as belt tensioners and a tyre pressure monitoring system also make up part of the standard specification.
New dimensions in driving refinement
The ultra-strong carbon-fibre-reinforced materials used for the new Mercedes-Benz SLR McLaren Roadster furthermore achieve a level of torsional stiffness that is unprecedented for an open-top car. This combines with a chassis bred on the racetrack and the 460-kW/626-hp AMG supercharged V8 engine to produce the sort of scintillating handling that is normally the preserve of super-sports cars with a fixed roof.
The SLR McLaren Roadster’s exceptional credentials are given a further boost by the fully retractable soft top that blends seamlessly into the vehicle’s flowing lines. The newly developed material it is made from not only promises everyday practicality in all weathers, it also enables the high-performance sports car to attain speeds which are highly unusual for a roadster. For example, the top speed of 332 km/h with the roof up matches the extraordinary figure set by the Coupe.
The air of a high-calibre Gran Turismo touring car
Despite the fact that the Roadster comes with a fully retractable soft top to fuse pure open-air motoring bliss with the ultimate in drive power, by no means do its occupants have to compromise on comfort or everyday practicality. As such, the new Mercedes-Benz SLR McLaren Roadster succeeds in synthesising high-tech from the world of motor racing, the capabilities of a thoroughbred high-performance sports car, as well as the long-distance comfort and sophisticated ambience of a classic, high-calibre Gran Turismo touring car.
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