Composite materials: greater than the sum of its parts

Penso have created a composite door for rail use which can see a 30% reduction on weight.
Carbon fibre is a textile product developed for an engineering industry that traditionally used metals.

Advanced and composites materials are becoming increasingly common. Ruari McCallion looks into the state of this particular union in the UK.

The key thing about composites is that they are stronger, lighter, more workable and can be produced in more complex forms than the material they are replacing, whether that is steel, wood, or even concrete.

They are generally lighter and often stronger – certainly so, weight for weight. They can be as simple as the GRP (glass fibre reinforced plastic) fascia in a car, or even a GRP garden fishpond; or as complex as the tub in a Formula One car or the wings on an Airbus.

Composites UK, the Trade Association, offers the view that, “a composite material can be defined as a combination of a matrix and a reinforcement which, when combined, gives properties superior to the properties of the individual components… the reinforcement is the fibres and is used to fortify the matrix in terms of strength and stiffness.

“The reinforcement fibres can be cut, aligned, placed in different ways to affect the properties of the resulting composite. The matrix, normally a form of resin, keeps the reinforcement in the desired orientation.

“It protects the reinforcement from chemical and environmental attack and it bonds the reinforcement so that applied loads can be effectively transferred”.

Composite materials form the backbone of renewable energy, where they are to be found in the blades of wind and subsea turbines; in internal and external applications in rail; in engineered structure and even in defence.

Developments in the wings include possible medical applications, using specialised materials at the nano level. But that’s in the future. There is plenty already going on, across a range of applications.

Thanks to its aerospace and Formula One motor racing segments, the UK is one of the world’s leaders in the development and use of composites.

Composites UK has more than 230 members, from Advanced Insulation Systems to Zwick Testing Machines.

Then there’s the National Composites Centre (NCCUK), in Bristol, which is the sector catapult. Practical, developmental and research activity is ongoing at a healthy rate.

“The most logical and cost-effective way to produce composites is in the form of wide sheets and rolls,” said Chris Lever, managing director of Bindatex Advanced Materials Cutting.

“However, these have to be cut or slit postproduction for the purpose of moulding them into the desired form. Tapes of composite materials are precisely laid adjacent to each other and then cured to form the required structure.”

This enables composites to be moulded into some pretty complex shapes – something that may not be generally known. After all, the most familiar sight of composites is in things like racing cars, aeroplane wings and large constructions.

Guy and his Gravity Racer at the summit of Mont Ventoux.
TT Champion, record holder and daredevil, Guy Martin, with the gravity-powered ‘soap box’ designed and made for him by epm: technology group and
Sheffield Hallam University Centre for Sports Engineering Research.

“If you are under the impression that composites are not ideally suited to complex shapes and structures then you have been misled,” said Graham Mulholland, managing director of epm: technology group. “We are constantly making intricate and complicated parts.”

They include a £4m contract for complex component assembly for an automotive client, which was announced towards the end of 2015, and demanding solutions for customers in the aerospace, motorsport and defence industries.

epm also points out that the old problem of composite production – time – does not necessarily apply; it can produce parts in as little as four minutes.

Complexity is something that Bindatex seems to regard as a speciality. “We slit prepreg (pre-impregnated) composite materials down to widths as narrow as 3.175mm, which then are wound onto finished slit coils, to meet the high tolerances demanded by aerospace applications,” Chris Lever said.

The manufacture of parts and components made from composites is, generally, highly automated, so it is crucial that the tapes themselves are accurate, to ensure precision throughout manufacturing.

Hypetex's ultimate goal would be the production of white carbon fibre.
Composite materials form the backbone of renewable energy, where they are to be found in the blades of wind and subsea turbines, among other uses.

Carbon fibre is a textile product developed for an engineering industry that traditionally used metals. Meeting very high tolerances on a fibre-based product is very challenging. Bindatex has developed bespoke machinery and invested a lot of time and money into meeting those challenges.

It seems its efforts have paid off, as the company announced in January this year that it has entered into a relationship with BAE Systems, to provide fast turnaround of advanced slit materials.

It will be processing composite materials to tight tolerances for use in a number of projects in the aerospace industry. Time is of the essence, even in an industry with long cycle times.

“The pace of the supply chain in the world of composites can be hampered by long lead times,” he said. “The aim of the partnership is to speed up the process for the benefit of the aerospace sector, which is one of the main industries we supply.”

Bindatex has also supplied precision tapes for a number of automated fibre replacement composite research programmes in cooperation with the UK Catapult Centres for High Value Manufacturing.

Bindatex has also supplied precision tapes for a number of automated fibre replacement composite research programmes in cooperation with the UK Catapult Centres for High Value Manufacturing.
Bindatex has also supplied precision tapes for a number of automated fibre replacement composite research programmes.

As well as precision, there’s another reason why time is a factor. “Many composites have a short shelf-life if kept at room temperature,” Lever explained.

“UD carbon fibre prepreg, for instance, needs to be stored at -18°C; otherwise, the epoxy resin begins to cure after about 30 days and renders the material useless. So it’s vital that we’re able to store materials, once cut, at low temperatures and ensure transportation is as fast as possible.”

Composite materials have been found to be appropriate for the most critical of structural applications – they are incredibly strong and can withstand impacts that would destroy even steel. However, that is a bit of their Achilles heel; when they fail, they do so suddenly and totally.

Vehicles that make extensive use of them – such as McLaren’s sports cars – build passenger tubs out of composite but surround them with aluminium parts in frontal and rearward orientations, in particular, as components that will deform and absorb energy, in the event of a crash.

The McLaren p1 GTR
McLaren’s vehicles make extensive use of composite materials, especially carbon fibre.

Stopping suddenly, even without sustaining damage to the cabin, can be as dangerous to fragile humans as the impact itself. But somewhere that is less of a concern is, for example, in engines. Rolls-Royce PLC is engaged in developing aero engines that will incorporate composite parts, including fan blades.

It is undergoing testing currently and are planned to be used in the next generation of UltraFan™ power plants. The carbon fibre fan system could reduce weight by up to 1,500lb (680kg) per aircraft, and they can help to save fuel in other ways.

Composites can withstand temperatures of up to 2,500°C, which is hotter than today’s jet engines – and the hotter a jet can run, the more efficiently it can use fuel.

Rolls-Royce has said that the use of composites and other advanced technologies could enable the UltraFan engine to be 25% more efficient than current models.

But all work and no play can make even the most interesting material lack joy. Guy Martin’s “Speed” adventures have caught public imagination, but there is still serious science going on.

Guy Martin’s “Speed” adventures have caught public imagination, but there is still serious science going on.
Guy Martin’s “Speed” adventures have caught public imagination, but there is still serious science going on.

Sheffield Hallam University’s near neighbour, the University of Sheffield has got into the “Physics is Fun” area as well.

A team from the Advanced Materials Research Centre (AMRC) built a prototype snowboard made of biocomposite materials containing flax, cashew nut husks and recycled plastic.

The team produced two boards from flax fibres embedded in a resin containing 30% cashew shell epoxy. The core was made from recycled PET foam, derived from old plastic bottles and other waste.

The board is light, transportable and can be as easily taken into a lecture hall, meeting room or laboratory as it can be carried onto the slopes.

While the snowboard is fun, it also serves as an effective demonstrator of the potential of biocomposites – and it does not have to be the size of an aeroplane wing to do it.

Whatever the industry or application, it seems that composites will be there.