The inerter was developed by a Professor Smith, of Cambridge University, England, as a solution to the age-old problem of balancing ride compliance with stiffness. A regular suspension set-up, be it on a car or motorcycle, is based around two components – springs and shock absorbers (dampers). Together these contribute to the car’s ride and handling, but no matter how the system is tuned, there is always a compromise between handling, comfort and grip. Even in racing machines, where comfort is less important, the suspension needs to be set to allow both sensitive handling, which requires a harder suspension, and a good mechanical grip, which requires suspension compliance.

The upshot is that there is oscillation of the suspension as the load on the tyres varies. If these oscillations reach a high enough frequency, the damper and spring package will not be able to react fast enough to damp them out, so tyre contact with the track surface will be reduced.

Prof Smith realised that this poor trade-off between handling, comfort and grip could be better resolved if a third type of component was added to a suspension system to make it more flexible – hence the inerter. Superficially it looks like a conventional shock absorber, with an attachment point at each end. In the case of a Formula One unit, the inerter will be attached to the suspension rocker and the chassis. A plunger slides in and out of the inerter’s main body as the car moves up and down. As this happens, a flywheel mounted on the plunger rotates in proportion to the relative displacement between the attachment points. The result is that the flywheel stores rotational energy as it spins.

In combination with the springs and dampers, the inerter reduces the effect of oscillations in the suspension and tyre, and thus helps the tyre retain a better grip on the track surface. By changing the weighting of the flywheel, the level of ‘inertance’ can be varied, allowing the effect on chassis behaviour to be fine-tuned; the latest systems even allow for the inerter to be completely disengaged in certain circumstances.

One area where inerters are of particular use is on vehicles with large tyre sidewalls, such as those in Formula One. A large sidewall is more prone to uncontrolled deflection at high suspension frequencies, which an inerter can be highly effective at combating, the result being a more consistent tyre contact patch and thus greater mechanical grip.

Speaking at the time the technology came into the public domain, in 2008, Prof Smith was surprised that no-one had thought of the idea before. “I was nervous about talking about the idea at first because it seemed so elementary a concept,” he said. “It was very difficult to believe that nobody had thought of it before, and I presumed that either it had been done already or there was some sort of snag.

“As I discussed the idea with colleagues, however, I began to realise it hadn’t been done and that it was possible to achieve this trade-off to improve vehicle suspension. The next question was whether it could actually be done, and once I had worked out what it should look like, that was a fairly simple matter."

Since these initial developments a decade ago, inerter technology has been refined to the point where it is now an indispensable part of a Formula One car’s chassis package. The technology has also begun to filter down into other series – for example, Porsche’s factory LM P1 is thought to use inerters, while they have also been widely adopted in Pro Stock drag racing, where they have allowed tuners to obtain much more consistent chassis set-ups.

Written by Lawrence Butcher

Traditionally, the usual material for exhaust construction in Formula One is either Inconnel or titanium, both of which provide relatively low weight, mechanical strength and reliability. However, with the weight of the exhausts sitting relatively high in the car, the potential gains from further weight saving are significant. 

Honda therefore developed a carbon-carbon (CC) exhaust system, which saw extensive dyno testing and some limited track use. Regular carbon composites, as used in panel work and chassis structures, use carbon fibres in a resin matrix. It is this matrix that is the limiting factor when it comes to temperature resistance, since although the carbon fibres themselves can withstand exceptionally high temperatures, most resins lose their integrity above 200 C. There have been recent developments in higher temperature resins, but there are none as yet that would survive reliably at the temperatures seen in an exhaust system. 

Honda’s answer was to use a CC material similar to that used for making brake discs and pads. It is a carbon fibre composite that uses carbon as a matrix, in essence a synthetic form of charcoal. While by no means weak, CC structures have nowhere near the mechanical properties of regular composites or metallic materials, so Honda’s development started with a target durability of 25 laps, aiming to use the parts for qualifying only. It began by developing collector and tail parts, but the ultimate goal was a complete set of CC exhaust pipes including the primaries, which if realised could net a weight reduction of 39% over the metal equivalents. 

Despite the challenges of using CC, there were other potential benefits in addition to the weight savings in terms of geometric freedom and packaging. For example, the use of Inconel entails the use of welded fabrication methods, which in turn requires that a certain material thickness be used to ensure weld integrity; it also limits the geometrical complexity of the parts. The CC parts are created in a mould, so such constraints were not a problem, and the result – Honda hoped – would be a lighter and more compact system.

Unsurprisingly, development was not trouble-free, and issues were encountered along the way, for example the integrity of the interface between the CC collector and the still Inconel primaries. CC has a very low coefficient of thermal expansion, and at operating temperatures gaps opened up between the two materials, making it hard for the engine control electronics to maintain a steady air-fuel ratio (which is measured using lambda probes in the primaries). To combat this, Honda developed a gasket material to fill the gaps. 

Additionally, the low resistance to oxidation of the CC material at high temperatures meant that a surface coating had to be developed to prevent this. Ultimately, the team was able to prevent surface oxidisation and maintain structural integrity for up to three hours at 900 C, which was found to equate to 30 laps at racing speed. 

Unfortunately for Honda though, regulation changes removed the possibility of running qualifying-only parts and ultimately the exhausts were never raced. However, the development process proved that the concept was feasible and it would be reasonable to expect that, given the renewed emphasis on weight saving in the new powertrains, such avenues of investigation may well come to the fore again.

Written by Lawrence Butcher

The catalyst for this move was a crash experienced by driver Robert Kubica at the 2007 Canadian GP, where the side of the car impacted a solid object at an acute angle. At the time of this crash, the side impact structures used consisted of straight carbon fibre tubes that extended out from the car at a 90º angle. Kubica’s crash showed that, while these existing structures were very effective at absorbing crash energy in a direct side impact, if struck at an angle the tubes were prone to break away, negating their effectiveness.

FIA Institute research consultant Andy Mellor, who led the project to develop a new structure, explained in 2013, “We went back to basics to examine what a side impact structure really needs to do in different types of accident. We used Robert Kubica’s crash in Montreal as a specific reference point since that was a major impact at an acute angle.”

To find a more effective solution, the FIA approached teams and asked them to come up with a new design that was effective regardless of the direction of impact. Three teams came up with designs, which included both improvements to the existing tube-based system and other solutions such as a layer of aluminium honeycomb material bonded to the outside of the monocoque. However, as can be seen in the video below, the honeycomb approach was unsatisfactory, with the material breaking away under certain loadings.

Ultimately, a solution devised by Red Bull Racing was settled on, and this consists of a series of laminated carbon fibre pillars, constructed in such a way as to crush during an impact rather than break off. These pillars essentially disintegrate under impact, in much the same way as a front or rear crash structure, absorbing the energy that would otherwise be transmitted directly into the monocoque.

Unlike the previous crash structures, which were built individually by the teams and had to undergo separate crash tests, the new side impact devices are a spec item. Exactly where they are mounted is still left up to teams, as each monocoque is unique, but the mounting points must be able to withstand horizontal loads of up to 60 kN as well as vertical loads of 35 kN without deforming.

Although the new structures provide a higher degree of safety for the drivers, they also present more headaches for teams’ engineers, as Eric Gandelin, chief designer for the Sauber F1 team, explained before the start of the 2014 season. “The new changes now regulate the design of the structures. This means the dimension of the tube and the laminate is now set and the same for all teams. And these tubes are overall much bigger and result in bulkier sidepods, especially compared to the very slim sidepods we had on the C32.”

Written by Lawrence Butcher

The basics of the metal-based SLS are exactly the same as with polymer-based SLS systems; however, the engineering challenge in its development was ensuring that the components produced have the mechanical stability to perform on a par with machined equivalents. Various Formula One teams have experimented with metal laser-sintered parts, with a high degree of success.

The process uses a more powerful laser than in the polymer-based system, to melt a metallic feedstock, the result being a fully functional metal part. Several manufacturers claim that parts produced using this process have mechanical properties on a par with cast or billet items.

The process is not yet perfect though, as the surface finish – a minimum surface roughness in the region of R_a (µm) 4 is achievable – is not sufficient for some applications, so post-production machining is often required. New developments are occurring rapidly, however, as the systems are refined and the properties of the finished parts improves, so it is highly likely that the time and cost savings will see metal laser-sinter produced parts appearing with increasing frequency.

Evidence of this is the fact that the variety of metal parts (as well as available materials) that can be produced using additive manufacturing processes is growing constantly. One company closely involved with Formula One teams in the area of rapid manufacturing has even gone so far as to produce a complete roll hoop to demonstrate the capabilities of its manufacturing process. A roll hoop is a complex component required to fulfil a number of critical roles. Its primary function is to protect the driver’s head in the cockpit, but other key roles are to act as an air intake for the car, a camera mount and a pick-up for other structures in the car.

The roll hoop is one of the highest points on an Formula One car, and a traditionally built roll hoop is a heavy component to have so high up. Any reduction in weight could be highly beneficial from a vehicle dynamics perspective, so the company set a target weight for the hoop of 1 kg – a potential weight saving of 1-2 kg over a traditionally manufactured item.

The resulting hoop (Fig. 1) contains internal features that would be exceedingly difficult and costly to produce using other manufacturing methods. The part has maintained its aerodynamic line, and features an area to allow for the addition of a camera mount or other component. It is produced from Ti6-Al-4V titanium alloy, so it is both lightweight and strong.  

The nature of this manufacturing process requires a support structure to be used when building any downward-facing surfaces, since the powder bed alone is not sufficient to hold the liquid phase created when the laser has melted the powder. The roll structure pictured was produced vertically, to demonstrate the capabilities of building tall components (the part stands 22.5 cm high). Only one small region under the front face of the hoop required support structures to be added for the build phase, while the rest of the design was self-supporting, minimising the need for support structures.

Although it has not been subject to FIA crash tests and is ‘generic’ in its design, it was modelled and subject to FEA assessment to ensure it would meet the same requirements as a traditionally manufactured part.  

Fig. 1 - A ‘generic’ Formula One roll structure made using the SLS process from titanium powder stock

Written by Lawrence Butcher

These advances have stemmed from the aerospace industry and, to a lesser extent, mainstream automotive production. These industries have invested heavily in automated composite systems in order to reduce the cost of series production parts. In Formula One, most parts are produced as one-offs or in very short production runs, so the benefits of automated production are not great. However, several manufacturers have indicated that they are investigating the potential of automated systems within Formula One and the broader motorsport industry. Whether they will see widespread adoption though remains to be seen, but it is pertinent to look briefly at the technologies available.

Resin transfer moulding (RTM) is the most common process currently used for larger scale production of composite parts. RTM uses a rigid two-sided mould set that forms both surfaces of a panel. The mould is typically constructed from aluminium or steel, but composite moulds are sometimes used, the two sides fitting together to produce a mould cavity. Once the mould is closed, the resin is introduced under pressure, filling the voids between the material tows.

This allows complex panels to be produced rapidly; however, the nature of the process results in a higher resin-to-fibre ratio than with traditionally manufactured pre-preg based parts. This has potential implications for the structural integrity of parts, meaning that components made using RTM may need to be designed with a greater volume of material to offset this weakness, impacting on overall weight. Producing the moulds can also be prohibitively expensive, especially where short production runs are involved.

Automated fibre placement is another area that has seen extensive advances and development of late. Instead of placing sheets of pre-preg material by hand, robotic arms places individual fibres automatically. The material is deposited by a specially controlled machine head that keeps the resin-impregnated fibres cold before laying and then heats them as they are laid, ensuring that they stick to the other fibres in the structure. After being laid, the machine compacts the fibres together using a roller system, removing the need for autoclaving. Because of the short production runs in Formula One, this technology has yet to catch on, but several companies involved in the sport are investigating its potential for producing parts that do not change during a season.

A similar process, automated filament winding, which works on the same basis but winds fibres around preformed mandrels, does see extensive use in the production of components for Formula One. For example, CFRP pressure vessels used for accumulators are made using this production technique, which allows for the relatively rapid manufacture of high burst strength, low weigh pressure vessels. 

Written by Lawrence Butcher

These developments are of particular interest to Formula One manufacturers, thanks to the often close proximity of composites to hot components. In recent years this has been a particular problem in relation to the use of exhaust systems to energise airflow over cars’ diffusers, a practice that inevitably involves hot exhaust gases passing over composite body panels.

With regular epoxy resins only being suitable for use below 300 C, teams have had to look at protecting these exposed panels or finding other resin systems to ensure structural integrity. The carbon fibres themselves will not fail due to exposure to high temperatures. In the extreme you can set fire to a section of carbon fibre epoxy composite and the fibre will be untouched; it is the resin system that will break down and burn off. With the reappearance of turbocharged engines in 2014, thermal management within the bodywork will be of even greater importance, with the desire to tightly package the outer bodywork being tempered by the very high temperatures surrounding the turbo unit.

One method of preventing heat damage is to apply barrier coatings to the external surfaces of the composite panels. Ceramic-based coatings are the most common, and are applied using a plasma spray system, creating a thermal barrier between the composite and the heat source. These coatings are often visible around the exhaust outlets at the rear of cars, thanks to the fact that they often have a textured finish and thus stand out from the surrounding painted surfaces.

Highlighting the level of detail engineering present in Formula One, this textured finish was identified as being potentially detrimental to the flow of exhaust gases being used to energise other overbody flow paths. As a result, one coatings manufacturer developed a smooth coating for applications where texture could present such issues.

Where coatings are not sufficient protection, teams must look to use high-temperature resistant resins to ensure components retain their integrity. For temperatures below about 430 C, cyanate ester-based resins are favoured. Originally developed by the aerospace industry for use in missile systems – which by their very nature see extremely high temperatures – such resins are seeing greater use in Formula One applications.

Cyanate esters are chemical substances generally based on a bisphenol or novolac derivative, in which the hydrogen atom of the phenolic OH group is substituted by a cyanide group. The resulting product with an -OCN group is named a cyanate ester. Much like the epoxy resins found in low-temperature materials, these esters can be cured by heating. The result is a thermoset material that retains its mechanical properties even at very high temperatures.

For applications that exceed the maximum temperature for cyanate ester-based epoxies, things get more complicated as suitable composites tend to require complex high-temperature processes for their production, and do not exhibit the same material properties as normal CFRPs. These include materials such as the carbon-carbon composites found in brake and clutch applications and ceramic-matrix composites, which can withstand temperatures up to 1000 C.

However, the appearance of a new generation of carbon fibre consisting of glass-ceramic matrices resulting from the polymerisation of inorganic polymers presents some interesting options for Formula One teams. These inorganic polymers are derived from alumino-silicate-based geopolymeric systems and, as such, differ significantly from both organic polymers and conventional ceramic matrices. The result is a lightweight alternative to metals and other materials for heat shields, ducts and other components exposed to temperatures of between 300 and 1000 C. The potential for this material is exciting for engineers as it opens up some previously unexplored applications for composites.

Written by Lawrence Butcher

Some of the biggest advances have been in the area of design and simulation. The behaviour of CFRP is considerably harder to predict than uniform materials: with finite element methods having been developed originally to model solid homogeneous and isotropic materials, simulations are naturally more complex for composites. The past decade though has seen the rapid development of new modelling techniques that can predict the behaviour of CFRP, providing engineers with a much deeper understanding of what is and isn’t possible.

The focus of these simulation and design packages is on the interaction between the separate plies of a composite structure, enabling components to be tailored to the load cases they receive, by optimising the composite lay-up (as in, for example, the number of ‘plies’ or carbon cloth layers, direction of fibre weaves and local addition of material in high-stress areas).

Not only did the introduction of CFRP construction into Formula One provide engineers with the ability to build cars that are lighter and stiffer than was possible using other construction techniques, it also brought great benefits to driver safety. These days, one of the most important milestones in a new Formula One car’s development is passing the mandatory FIA crash tests. While it is still a struggle for some teams to pass these tests – usually those lower down the grid with less powerful development facilities – they do not prove problematic for most.

It is the failure mode of composites that makes them hard to model. Traditional metallic structures absorb impact energy by deforming and folding; CFRP is very different, as the energy is absorbed by fracturing. The static simulation of CFRP is now well-developed, but accurate prediction of crash performance is somewhat harder, with FEA (finite element analysis) requiring significant real-world testing, reducing the benefits of FEA as a tool here.

New processes, however, allow accurate predictive FEA simulations based on more economical testing of small material samples, or ‘coupons’. The coupons are placed in a fixture in a compression test machine, then crushed at a variety of speeds, and the results of the tests inform the basis of the material properties and behaviour modes for the analysis. Overall though, composites are largely unrivalled as a material for impact absorption, with a specific energy absorption (SEA, measured in kJ per kg of material used) far higher than their metallic counterparts – providing sufficient optimisation has taken place of course.

The decision to use CFRP for impact absorption is a fairly easy one. Comparing the SEAs of various materials, steels achieve about 12 kJ/kg while aluminium reaches around 20k J/kg. However, a well-optimised carbon fibre structure – that is, one with an optimised lay-up/fibre orientation and component geometry – can absorb anything from 40 kJ/kg up to 70 kJ/kg in a highly refined and tested design.

Suffice to say, from a safety perspective, CFRP does not look likely to be superseded as Formula One’s material of choice any time soon.

Written by Lawrence Butcher

To this end the Formula One technical regulations require chassis to pass a series of impact and intrusion tests before they can be used in competition. This requirement was first introduced in the mid-1980s, and it is no coincidence that the evolution of this testing has led to a situation where accidents involving Formula One cars that result in serious injury or loss of life are nowadays extremely rare.

The path to the current ‘safety capsule’ Formula One monocoque began in the early 1980s with the adoption of carbon fibre composite materials for chassis manufacture, although in the strict definition of the word, composites had already been in use in motorsport since the 1950s in the form of glass fibre moulded body panels.

The first Formula One car to be raced that incorporated composite material in its chassis was the 1966 McLaren M2A, which featured panels of Mallite – a composite formed of aluminium sheets over a core of end-grain balsa wood. Although the McLaren benefited from a chassis rigidity advantage over its rivals, the technology was not pursued in later models.

Carbon fibre was first used in motorsport in the late 1960s as reinforcing strands bonded to the large glass fibre body panels of sports racecars, and was first seen in similar applications in Formula One in the early 1970s. Its first use as a structural material came when the McLaren and Lotus F1 teams both introduced carbon chassis in 1981. McLaren subcontracted the manufacture of this first model to Hercules Aerospace in the US, while Lotus opted to build theirs in-house. The McLaren was built using moulding and layout methods that were the forerunners of the techniques still used today. Lotus opted for using folded sheets of composite material in a similar manner to the way chassis had previously been fabricated using sheet aluminium and aluminium honeycomb.

Pioneered in aerospace applications, carbon fibre materials are produced by the application of a thermal decomposition process on a fibre precursor. The materials most commonly used in Formula One are based on a polyacrylonitrile (PAN) precursor, other precursors include Rayon and pitch fibres. According to the desired molecular structure of the finished material, the PAN precursor is co-polymerised with one or more of a range of monomers such as acrylic acid or methyl acrylate. Decomposition of the precursor allows it to be extruded into a filament via a winding process before it is subject to an oxidation phase in which heat is applied over a period of time with the filament held in tension. The resultant thread can then be woven into carbon fibre fabric.

A Formula One monocoque is manufactured by hand, the low volume-high performance requirements of motorsport making automation of the process impractical. Plies of carbon fibre fabric – pre-impregnated with resin – are laid up in mould tooling to form the outer skin of the structure. A hollow-cell core material is added before further plies of carbon fibre fabric are introduced as an inner skin. According to the anticipated loads on varying areas of the structure, fabrics with differing weave patterns and in varying orientations are deployed.

The basic materials and methods used to manufacture a Formula One monocoque have remained largely unchanged for more than 30 years. However, many scientific research groups are engaged these days in the development of nano-materials which are widely seen to be the future of composites. Currently the only mention of nano-materials in the FIA Formula One technical regulations is the banning of the use of hollow carbon nano-tubes in the chassis structure. Other nano-materials such as graphene are effectively outlawed by the simple fact that none can be supplied in sufficient volume at the present time to make their use viable. Nano filled resins could prove to be an interesting area of development, with the promise of increasing resin toughness and thus dynamic crash structure behaviour.  

Basalt fibres are still not widely available but could prove an interesting alternative to glass and carbon fibres in terms of both cost and performance. Whether such a material would penetrate the Formula One market is unclear, as typically the teams opt for performance over cost.

Fig. 1 - A Formula One monocoque cocoons the driver in a carbon fibre safety cell.

Written by Alan Lis