- Published in Features.
Whatever energy source gets the wheels turning, vehicles become more efficient if everything can be made lighter. OEMs are investing more than ever in lightweight design, and premium manufacturers in particular are spending a lot of their R&D budgets on composites research.
The materials of most interest are carbon fibre- and glass fibre-reinforced plastics. The former has the best performance but the latter is less expensive and is likely to find far more applications, and more quickly.
Glass-reinforced plastics are widely used already, for example in some chassis parts such as anti-roll bar drop links. But these components derive their strength from short glass strands. Chemical supplier BASF wants to go further, and has developed long glass-fibre technology.Working together with engineers from Daimler, BASF’s researchers put their know-how into a lightweight Smart car project to showcase possible applications for these higher-performance composites.
Perhaps the most ambitious applications – but also the most challenging – are the wheels. They're subject to high static, dynamic and fatigue loads, and also suffer high abuse loads when consumers drive on, off and into kerbs. They also add a lot of value for OEMs as bigger, more expensive rims are often selected from the options list.
BASF has been working on long-fibre technology for the past couple of years, and has refined its in-house modelling tools to better predict the injection-moulding process and how the wheels will behave under load.
“The decisive thing is that we can simulate fibre orientation – this significantly determines the properties,” says Dr Christian Fischer, BASF’s president of polymer research. “And we can simulate high-speed crash performance. With these data we could convince Daimler of the potential.”
Most glass fibre used in series production is the so-called short type: each strand is less than 1mm in length – or around 350 microns, Fischer says. BASF's fibres are 10mm long. These make composites much stronger and much tougher but by how much depends strongly upon fibre orientation – unlike short strands this cannot be random – which is why so much of the work has gone into process simulation.
The base plastic is polyamide. Fischer says it’s too early to say which grade he's using but he is very pleased with the results: “Each wheel saves 3kg compared to aluminium – so 12kg for the whole vehicle – and because it’s unsprung mass it’s even more significant.”
Daimler is excited about the technology, Fischer says, but the big task now is to prove everything works through an intensive testing phase, including fatigue and crash.
Cost will also play a big part in deciding if and when composite wheels will appear in series production.