Lose weight with composites

Carbon fibre. Photo: istockphoto

Lose weight with composites

Lightweight material structures based on fibre-reinforced plastics (FRP) improve the environmental performance of cars

Low weight and high stability – essential features of materials that are being used currently and for the foreseeable future to accelerate or decelerate masses in an efficient, environmentally sound and economically viable way. Heavy steel car bodies are considered to be a relic of the past in the meantime. Cars made from composite materials consisting of fibres and plastic (FRP) are where the future lies. If experts are to be believed, FRP are stimulating not only car or aircraft manufacturing but also many other application areas, such as renewable energy generation or machine manufacturing. K-online.de takes a look here at the potential of and applications for fibre-reinforced plastic composites, with particular emphasis on carbon-fibre-reinforced plastics (CFRP) with their lightweight, crashproof and non-rusting properties.

 
 
Quelle: istockphoto

The EU Parliament is sticking to its target of reducing the CO2 emissions of cars.

The European Union (EU) is exerting pressure and is pushing the car industry to reduce weight. Last month, the EU Environment Committee took the decision to lower the exhaust limits for cars to 78 grams of carbon dioxide (CO2) per kilometre driven as of 2025. [1] At the same time, the EU Parliament is sticking to its target of reducing the CO2 emissions of cars to 95 grams by 2020 and to 130 grams by as soon as 2015. [2] The question is how these targets can be met.

Particularly in view of the fact that cars are tending to get heavier and heavier due to higher horsepower (hp) as well as to the desire and need for extensive safety equipment and comfort facilities. By way of comparison: in 1975, a VW Golf I weighed about 780 kilograms; today a small or medium-sized car generally weighs about 1.2 tonnes. [3]

This increases costs and is bad for the climate too, because – as is a well-known fact – more weight leads to higher emission of carbon dioxide (CO2), which has a negative impact on the environment. This situation is proving to be a dilemma rather than an insoluble problem, however.

 
 
Plastic versus steel. Source: istockphoto

The problem can be solved by the intelligent substitution of such heavy materials as steel and aluminium.

Lightweight structures are a solution

The problem can be solved by the intelligent substitution of such heavy materials as steel and aluminium that are generally used in automotive manufacturing by very much lighter but no less efficient chemical / polymer materials - particularly composites, as fibre-reinforced plastics (FRP) tend to be called nowadays. The following example demonstrates how important lightweight structures made from FRP are for the transport industry:

“Every reduction in car weight of 100 kilograms cuts fuel consumption by 0.1 – 0.8 litres per 100 kilometres, depending on how the car is driven. 30 per cent of such a saving can be achieved with lightweight structures, which shows that such structures are the major source of reductions in fuel consumption and carbon dioxide emission. Improvements to engines only have the potential for reductions of 15 per cent, on the other hand.” [4]

 
 

Potential identified long ago

The trend towards the substitution of metals by less heavy polymer materials is noth-ing new in the automotive industry. The list of vehicle parts that have been manufactured from various plastics for some time now is long. It consists of about 2,000 different items, including: bumpers, front end, radiator grille, mirrors, sliding roofs, body parts, oil sump, fuel tank, hubcaps, headlights, windscreen wipers, glazing, decorative elements, damping elements, gaskets, sunroofs, dashboards, car seats, steering wheel, headrests, accelerator, brake and clutch pedals, gear lever knob, door side panelling, rear shelf, carpeting, roof lining, airbags, side impact protection, intake pipes, hose systems and many others besides.

Quite apart from the fact that plastics weigh less than metals when they have the same dimensions: they do not rust and do not therefore need to be given surface treatment or a paint finish, depending on the application. Another advantage: pol-ymers / synthetic materials help to protect the passengers (airbags, seat belts etc.), have a unique feel and increase the possibilities available to car designers considerably.

 
 

There is no alternative to lightweight structures

At the 23rd Stuttgart Plastics Colloquium that was held in March this year, Professor Peter Middendorf pointed out, however, that there have been no signs of a real trend towards lightweight structures involving the use of FRP in car manufacturing in recent years, even though the environmental performance of cars may well have improved: the reductions made in fuel consumption have been achieved primarily by better drive technology and aerodynamics [5]. There are limits to engine performance and body design, on the other hand. From the long-term perspective, more extensive concepts are needed.

The scientist from the Institute for Aircraft Manufacturing at Stuttgart University con-cludes that “the increase in demands for comfort, safety, reliability and many addi-tional functions that are standard in series production today” is the main reason for the steady increase in vehicle weight in the course of time. He thinks this is a trend that will be continuing in future as well, for example “if and when weight is increased significantly in the context of developments in electromobility due to the electric motor and, above all, battery packs. This would () shorten the range of the vehicles too and, perhaps, make them unattractive ()”. The car industry could only counteract this if it succeeded in compensating for additional weight via lightweight structures, i.e. () involving fibre-reinforced composites.

 
 
Airbus A380. Source: Airbus

25% of the Airbus A380, for example, is made from plastic reinforced with carbon fibres (CFRP).

Aircraft manufacturing has assumed a pioneering role

Middendorf says that aircraft manufacturing, which can probably be considered the most important trendsetter in the use of fibre-reinforced plastics (FRP), demonstrates how this can be done. Fibre-reinforced composite plastic materials have been in operation here for years now. Modern aircraft concepts have opted for the smart combination of different materials. 25% of the Airbus A380, for example, is made from plastic reinforced with carbon fibres (CFRP). The result: a reduction of 15 per cent in kerosene consumption. The aircraft manufacturer Boeing is going one stage further: plastics already account for 50 per cent of the Boeing 787 Dreamliner, due in particular to CFRP wings and fuselage structures. This is leading to substantially lower emissions of gases that are harmful to the climate during operation. [6]

Middendorf thinks that the maximum possible has been achieved for the foreseea-ble future, however. The scientist gives the high price of carbon as his reason for thinking this; it is in addition an extremely laborious and expensive process to manu-facture FRP components. This is attributable to the tremendous amount of manual work that has been needed up to now in the manufacturing process; the quality demands made on the composite materials and the need for minimum tolerances have had an additional impact.

Middendorf says that the comparatively high material and manufacturing costs pay for themselves even so. The scientist calculates that an Airbus A320 with a maximum take-off weight (MTOW) of about 73 tonnes consumes some 2,000 litres less kerosene per year when the aircraft’s weight is reduced by only 10 kilograms. This reduces environmental impact and cuts costs, while it also creates attractive alternatives for the manufacturer, since he can – for example – take advantage of the potential of lightweight structures to increase the range or payload of his aircraft or to improve passenger comfort.

Middendorf points out that more automated and thus more cost-effective manufacturing processes need, however, to be developed in competition with other lightweight materials in response to steady growth in the number of aircraft delivered.” This is a concern that the automotive industry and its suppliers have to face too.

 
 
Source: istockphoto

Carbon-fibre-reinforced plastics have tremendous potential as a material for lightweight structures.

Tackling the challenges of manufacturing technology

Car manufacturers have opted to adopt different approaches in the lightweight structures they have introduced primarily in the higher-priced premium segment, ranging from hybrid materials to hybrid structures and bodies made entirely from CFRP. Middendorf is, however, convinced that cycle times and component costs need to be reduced, in order for CFRP components to be used in large-scale pro-duction and for the full potential of the composite material to be exploited economically viably in specific applications as a result.

This means that the price has to drop first before the material can be used in mass production. “Carbon-fibre-reinforced plastics have tremendous potential as a material for lightweight structures”, says Professor Holger Hanselka, Chairman of the Fraunhofer Group for Materials and Components – Materials. Hanselka is therefore emphasising what Middendorf says. He stresses that CFRP materials with the same strength properties weigh only about half as much as steel; CFRP are, in addition, crashproof and do not rust. CFRP components do, however, cost six times what identical components made from steel cost – partly because CFRP components generally have to be produced manually. Series production in large numbers is, in addition, hampered by the long time it takes to manufacture components: polymerisation using epoxy resin as the fibre matrix takes many hours. Another issue that has not be settled satisfactorily yet is recycling of the composite material. A wide range of interesting concepts for potential solutions are, however, in the process of being developed in the scientific and industrial communities.

 
 

Concepts for an automation solution

The Fraunhofer Institute for Chemical Technology (ICT) in Augsburg / Germany has developed an innovative new manufacturing process for the car industry that enables the production of CFRP components to be automated completely. The new process combines a braiding machine of the kind that is normally used in the textile industry with a pultrusion machine of the kind that is used to manufacture fibre-reinforced plastic profiles in a continuous process. The braiding machine gives the dry carbon fibres the right structure and the pultrusion machine encases them in resin – all of this being done fully automatically. The fibres no longer have to be placed and aligned in the mould manually, as has been standard procedure up to now.

The car manufacturer BMW is demonstrating that mass production of CFRP components is possible on an economically viable basis. The electric car BMW i3, which the company says will be available in a few months, has – among other things – a CFRP passenger compartment that is manufactured in series production. A “revolution in manufacturing technology” is how the car manufacturer from Munich in Germany has announced this development emphatically: “Carbon components are not just revolutionising lightweight structures. They are also making it possible to create new shapes in vehicle design, since the plastic that is reinforced with carbon fibres is almost as easy to process as textile fabrics when it is dry. As a result of this, bodies made from carbon provide more space inside, on the one hand, while they also enable more complex, aerodynamically optimised car design at the same time. And – last but not least – carbon is an extremely strong material that increases the safety of all the passengers in a BMW i.” [7]

 
 
Source: istockphoto

CFRP have already been introduced in high-tech sports equipment.

Other potential applications for CFRP

“As a general rule, lightweight structures are always an attractive option when masses are accelerated or decelerated.” Middendorf says that this is the case not only in the transport industry but also in such areas as the generation of wind energy, which represents a challenge for lightweight CFRP structures due to increasing rotor diameters and blade lengths of up to 80 metres. Gas fibre reinforcement is still the state of the art solution here, which is less expensive than carbon. The use of CFRP materials is, however, said to be of great interest for large equipment because of their weight-specific properties. What is crucial, the scientist says, apart from the price of the material is, above all, automation of the manufacturing technology; this issue will be playing a major role in future, particularly in order to gain a competitive edge on the market and to obtain a technological lead.

As far as technological leads are concerned, lightweight CFRP structures could play a central role in machine manufacturing in particular, the heart of which consists of drive machines and moving parts. Such lightweight CFRP structures have already been introduced in high-tech sports equipment, “for which a substantial proportion of global carbon fibre production is used”, Middendorf reveals.

One of our next Topics of the Month will be looking at the question of the role that polymers and fibre-reinforced plastics are playing in space technology.

 
 

Background

[1] www.spiegel.de/auto/aktuell/eu-parlament-beschliesst-strengere-co2-grenzwerte-fuer-autos-a-896338.html
[2] EU Regulation to reduce CO2 emissions from cars, German Ministry of the Environment, Nature Conservation and Nuclear Safety, Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit
[3] B. B. Niesing: Carbon in Serie. Weiter vorn – Das Fraunhofer-Magazin 3 (2012) 8-13
[4] W. Beck, R. Kopp. H. von Hagen, P. Hohmeiner: Leichtbau durch Konstruktion und Form. Horizonte (1999) 248-255. ISBN 3-540-66373-8
[5] P. Middendorf: Potenzial und Einsatzgebiete von FKV für Leichtbauanwendungen. 23rd Stuttgart Plastics Colloquium, 6./7. March 2013
[6] G. Deußing: Plastics move the world – material of the 21st century. K-online.de Topic of the Month July 2012. .
[7] www.bmw-i.de/de_de/concept/#der-beginn-des-carbonzeitalters
[8] W. Michaeli, H. Greif, L. Wolters, F.-J. Vossebürger: Technologie der Kunststoffe, Carl Hanser Verlag, München, 2008