Will carbon fibre ever be a cost effective alternative to traditional materials?

Optimisation of composite structure is reaching remarkable levels. Indeed, a recent project by two former McLaren designers shows just how light you can go if you really know what you are doing. The pair formed RPx Automotive and want to be at the forefront of the new generation of vehicles that use low weight structures rather than engine power to achieve high performance. A single-piece carbon composite prototype structure known as a 'tub' has been produced by Future Fibres and partner Persico Spa for RPx. Amazingly the tub weighs just 35kg with the complete car expected to weigh just 480kg. Yet, the strength and stiffness remain uncompromised. Despite being impressive, the car is still likely to come with a hefty tag. However, the concept of using a single tub as the primary structure of a vehicle is still relatively new. Doing away with much of the assembly and joining currently needed for metallic structures does pose an interesting proposition. So, could the technology ever be cost-effective enough to make it to the mainstream? "Look at any high-spec material and over time it does filter down," says Charlie Gough, business development director at Future Fibres. "Already, the raw material of carbon is coming down as more people use it and more people produce it. "There are newer materials that people are looking at all the time. Graphene is now being talked about and so are carbon nanotubes. Both are outrageously expensive. This is what carbon fibre was in the 1980s. However, steel has been around a long time and is still much cheaper to produce." Though being more closely examined by many engineers on the periphery, carbon fibre is still considered too expensive by most. There are many applications that could benefit from lightweighting, but simply can't justify the cost. However, while the material has a premium price tag, through-life costs often show a competitive benefit. Aerospace, aviation and the marine industries have already bought in to this philosophy. And, while they have paid a premium at the outset, they are finding reductions in operation and maintenance costs. The problem lies in convincing a purchasing manager or financial director about the lifecycle cost benefit versus purchase cost penalty – or in tendering for a project with a higher initial cost but trying to convince the client of the benefits of lower through-life costs. It is a tough sell that many industrial applications have yet to make. "Certain fields won't use stainless steel because galvanised is cheaper," says Gough. "So a jump to carbon fibre composite is just too expensive; they won't even consider it. It might be two or three times the cost at the beginning but over the life of a part, composites can work out cheaper. The benefit is quite often in the through-life costs." Bridging the benefit Installations costs, operational costs, longer life and lower maintenance are all potential cost savers. As a result, Future Fibres was able to introduce some of the other benefits composite material offers, alongside lightweight, to a stress ribbon bridge constructed in Cuenca, Spain. It provided wound, unidirectional solid carbon fibre cables as the primary load bearing supports to the footbridge that were 80% lighter and 50% stronger than stainless steel rods of a similar stiffness. The cables support the bridge platform and needed to meet both the strength and stretch characteristics specified by the bridge designers. The bridge uses 16 lines of cables, made up of five individual cables joined with linked plates to 80 43.4m-long, solid carbon cables has a working load of around 95 tonnes but a diameter of just 42mm. "The cables weighed less than 100kg each and could be handled by two guys," says Gough. "The rigging company normally allowed themselves three weeks to install wire cabling of a similar size but with the carbon cables they did it in two days without any heavy machinery or anything." The use of carbon fibre cables meant the unsupported spans could be increased and supporting structure reduced. Installation time and cost was reduced by over 80%. The maximum span was increased from 30m to 72m to add strength and reduce weight. This meant that, instead of having five vertical pillars holding the bridge up, it actually only needed two. The reduced weight also meant that around 30% less concrete could be used. "If you compare a wire rod with a carbon rod, it is going to be a lot more expensive," says Gough. "There is an initial cost upfront which is more than the traditional route. However, there are savings. For this project I thought the big selling point was the reduction in raw materials such as the saving of concrete because of fewer pillars, quick installation and the elimination of machinery. However, despite talking to the client about all the benefits they can have right now, actually the big driver for them was the perceived 'near-zero' maintenance over the next 50 years." Future Fibres has its roots in the marine industry where it has pioneered the use of continually wound, unidirectional composite fibres for yacht rigging. It has become an expert in composite technology and is now focussing on developing new markets, and finding new applications, where composites have not yet been considered. As well as bridges, this brought them to identify cranes as having potential for benefit. Weight reduction and improved fatigue resistance in a composite cable offer the potential to lift 20-50% more, which may allow crane owners to charge operators a premium for their use. The cables should also outlast the rest of the structure and installation is relatively straightforward. "It might be two or even three times more expensive than traditional materials," says Gough. "However, over the life of the crane you normally have to replace the pendant three times, and routinely carry out maintenance. Composite cables are again likely to result in very low maintenance and offer zero creep during installation. So over its life you are actually making a saving over traditional steel cables." Composites are certainly not for everyone, but the case for them and their effective application is becoming ever more widespread. The ability to tailor the material properties and its excellent through life characteristics are making it increasingly competitive in more traditional applications, provided through life benefits are taken in to consideration at the outset. As always, it is a case of using the right material, in the right place. However, don't dismiss what appears to be an expensive exotic material just yet, as it could offer you some unexpected cost benefits and unique performance advantages.