Material witness

The National Physical Laboratory tests the composition of metals used in Formula One cars. And its rulings are just as stiff as the competition on the race track. Max Glaskin reports.

It’s not easy enforcing the rules when the stakes are high. That’s why the FIA governs Formula One with a rod of iron. It could, instead, use a bar of metal matrix composite (MMC) but its own regulations restrict the use of this exotic material. And to make sure none of the race car constructors even attempt to bend the rules around this extremely stiff and light metal, the FIA has appointed independent experts at the UK’s National Physical Laboratory (NPL) to be material witnesses.

NPL is the country’s measurement house, owned by the government and operated on its behalf by SERCO. Its principle research scientist Jerry Lord is in charge of the FIA task and he recalled how the unusual contract was won. ‘The FIA approached us towards the end of 2001,’ said Lord at NPL’s smart new laboratory in Teddington, Middlesex. ‘They wanted us to give them some advice on testing because there’s a regulation on the specific stiffness of the materials that can be used in F1.’

According to article 15.1.2 of the FIA regulations, metals with a specific modulus greater than 40 GigaPascals per gram per cubic centimetre cannot be used. To ensure nobody exceeds this, any metal with a specific modulus greater than 35GPa/g/cm3 must be submitted for independent testing. Out of all the materials used by F1 teams, only MMCs can approach this figure — and they can readily be configured to exceed the permitted maximum.

MMCs can be created in several ways but the starting point is usually aluminium. A powder of the metal is mixed with another material which, in the case of motorsports components, is normally fine particles of the ceramic silicon carbide. They go through high energy mixing followed by solid state compaction into a billet for further working. The MMC is lighter and stiffer than aluminium and titanium, though it is more expensive than both.

For Lord it was first a matter of choosing the most appropriate test to see if the MMCs being used by F1 teams complied with the FIA’s regulation. ‘Two methods had been proposed and we did an initial assessment of them both,’ he said. The NPL team considered a tensile test, which has been around for about 100 years, and a dynamic method where the material is struck and the resonance measured. ‘We chose tensile testing, and developed it so we can focus on accurate strain measurement and data analysis.’

Put simply, a 100mm sample of the machined material is gripped and pulled and the displacement measured. This parameter, Youngs Modulus, is then divided by the density to give the specific modulus. The report is sent to the materials supplier which is bound to inform its F1 team customers of the result. Too high and they mustn’t touch it. ‘Although the limit is 40GPa/g/cm3, in practice the maximum is 39.5 because we know that there is a small amount of uncertainty in our test set-up,’ said Lord.

He is pleased to be offering such an expert service to an industry in which success is measured in fractions of a second. ‘Precision measurement and advanced materials testing are helping to create high-performance vehicles that are safer but without reduced performance,’ he said. The NPL test means the materials suppliers have been able to tweak the compositions of their MMCs to get as close to the limit as possible. So the accurate measurement is supporting the development of new materials for F1. NPL’s guidance is helping teams to characterise advanced aluminium and titanium alloys to reduce component weight while maintaining stiffness and performance.

At the same time the requirement is helping the F1 teams to have greater confidence in the quality of their own test data and therefore their ability to comply with FIA specifications. Among those to benefit is the Red Bull team. According to Lewis Butler, Red Bull’s senior structures analyst, innovations such as the development of MMCs are vital to being competitive. ‘There is a considerable gain in efficiency per unit mass,’ he said. ‘We can minimise the mass of the part to give the highest performance for given stiffness targets. It is, however, more difficult to machine than most other conventional alloys.’

MMCs haven’t always been so tightly controlled. A dozen years ago they were used for brake callipers which were said to have saved a second per lap in competition. Indeed, Champ cars in the US still use MMC callipers because they last up to four years before needing to be replaced. The material has properties of low wear and friction which make it appropriate for use in engines as cylinder liners, connecting rods and pistons but these applications are off-limits to F1 constructors teams. Fears that the cost of the material would make it unaffordable to all but the richest F1 teams led to the FIA restrictions. Now it is used primarily in the uprights and the rockers of the suspension systems.

The restrictions are a fact of motorsport life that is accepted by some and not others. ‘The FIA regulation is a hindrance to designers and engineers but is a help to the governing body in terms of controlling costs,’ said Lewis Butler at Red Bull.

Whether the MMC regulation really is effective at controlling cost is a matter for debate. Materials account for only about two per cent of an F1 team’s annual budget and the current high price of titanium means that MMC is relatively less expensive than it was. The Champ car experience with brake callipers lasting four years has shown that in the long term the material can actually reduce costs. And how much would it cost using aerodynamic analysis, for example, to save one second per lap?

The cost of materials is closely related to volume of production and some say that the restrictions on MMC use by the FIA are actually helping to keep the price up. Industry sources say that if it becomes derestricted, volumes would rise, prices fall and it would become accessible to a whole new tier of customers. Instead of remaining a rare and exotic material it could be used well beyond its current niches within the automotive and industrial sectors.

These are arguments being put forward by some teams which feel the materials restriction is not helping the sport and they are putting some pressure on the FIA to alter article 15.1.2. Not surprisingly, these political points have brushed past NPL’s Jerry Lord and there have been attempts to influence the reports from his lab. ‘We have had a bit of pressure put on us by one or two of the teams, to steer my comments and conclusions following tests on MMCs,’ he said. Did he waver? Like the reputable independent measurement laboratory should be, and like the stiffest MMC could be if the FIA allowed it, he was inflexible.

This impartiality is standing NPL in good stead and has won it new business. ‘We have been asked to advise on checking whether the materials that have been tested in the lab are the ones that are actually used on the car,’ said Lord. ‘The FIA is interested in fingerprinting the materials. At this stage we have been asked to advise on the feasibility of the work. It will involve chemical analysis to break down the composition of the material. But how do you cut a piece off an F1 car without affecting its performance?’ Not even NPL can bend the laws of physics.

Max Glaskin