Driving forward with composites

Materials World magazine
1 Sep 2008

The Caparo T1 track car, made using novel manufacturing techniques for carbon composite parts, is in its final lap as the first production specification vehicles are to be launched later this year.

Unwilling to reveal too much at this stage, Caparo, a manufacturer of steel, aluminium and composite products that is headquartered in London, UK, explains that its forming technique is adapted from another area of polymer engineering. It aims to make carbon composite parts more affordable for use in roadcar applications as the automotive industry attempts to lightweight vehicles to reduce carbon emissions and improve fuel economy.

A number of the T1’s components, including the steering wheel, chassis and front crash structure, are made from a sandwich construction monocoque that comprises an aluminium core with carbon composite skins. These use a carefully optimised mix of woven and uni-directional carbon fibres.

Ben Scott-Geddes, Engineering Director at Caparo Vehicle Technologies, says, ‘Carbon composites allow us to design structures which achieve the same [properties] as conventional materials [steel and aluminium] but with substantially less mass.

‘Composites also absorb large amounts of crash energy – typically around five to six times more per kilogramme than steel and two to three times more than aluminium. The cored structure increases specific modulus, providing further improvements in crash response’.

However, unlike in aerospace, which has driven development in this area, cost has been a prohibitive factor for composite use in the automotive sector.

A US$10m pilot plant is now being built in India to produce high volume parts using Caparo’s technique, which is said to reduce cycle time.

Scott-Geddes adds, ‘The main challenge has been the cost of raw materials. [However, high] volume commitment should be rewarded with lower price. Caparo is in discussions with raw materials suppliers’.

Alongside manufacturing, fundamental materials research at Caparo has involved examining how the carbon fibres are manufactured and the effect of this process on their crystallography. This allows their properties to be optimised for strength and toughness, and the right blend of fibres, such as carbon with alternative local reinforcement, to be specified for an application.

The company is also working on alternative matrix materials using thermoplastics, polycarbonates and sheet moulding compounds (the latter comprise glass fibres and a paste containing thermoset and thermoplastic resins and calcium carbonate fillers). ‘Caparo’s new “variable matrix” uses
greatly improved in-mould flow properties to allow several of these materials to be combined in a single component, again to optimise local properties,’ says Scott-Geddes.

The aim is to produce 100,000 highly efficient lightweight composite vehicles per year within 15 years, with a cost comparable to today’s cars.

The Caparo T1 also makes use of new monoblock technology for brakes, whereby the entire calliper is made from a single billet of aluminium to make it extremely light and stiff.

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