For reasons that have been explained in depth in various other F1-Monitor articles, composites are still the favoured material for the construction of much of a modern Formula One car. The composites industry is constantly evolving and new materials with improved properties are being developed. One area of advancement with particular relevance to racing applications has been the development of CFRP (carbon fibre reinforced polymer) varieties that can resist high-temperature environments while retaining their mechanical properties.
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