Motorsport Composite Fundamentals: Carbon Fiber

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Carbon Fiber

05.36

00:00	Carbon fibre is often put on a pedestal even by those who don't really understand it, and that's for good reason.
00:06	It's undeniably a staple in motorsport and has some great properties that lend themselves to performance applications.
00:13	Carbon fibres are made from organic polymers, which basically just means that they contain at least one carbon atom.
00:20	The polymer is almost always polyacrylonitrile, or PAN for short.
00:26	They are spun, stretched and chemically treated to produce filaments around 5-8 microns thick, or about a tenth of the thickness of a human hair.
00:36	It's not overly important how our fibres are made for the purpose of this course, but put simply, these filaments are superheated and carbonised into almost pure carbon.
00:46	From here they grouped together into what's called tow, which can be used as is, or turned into fabrics for use as reinforcement in a resin matrix to construct a composite, similar to what we discussed with fibreglass in the previous module.
01:00	There are many different forms of carbon fibre reinforcements, like non-woven cloths such as CSM, as well as woven fabrics, tapes and ribbons.
01:09	Fabric that has been pre-impregnated with near -perfect resin content is also available and is known as pre-preg.
01:17	But we'll get into this and all the different forms of reinforcement later in the course.
01:21	Next, let's discuss the properties of carbon fibre, as this is where it really shines.
01:26	The key advantages of carbon fibre is its strength to weight ratio.
01:30	It's extremely strong for its weight, so it makes a great option for parts that need to be strong but also light, which is often the case for race cars.
01:38	As we mentioned previously, this ratio is significantly higher than that of fibreglass, specifically e-glass, and multiple times higher than steel or aluminium.
01:49	Probably more impressive though is its stiffness to weight ratio, making it great for aero components or suspension components as well as chassis structures.
01:58	This ratio is about five times greater than that of e-glass.
02:03	This stiffness also results in good resistance to buckling.
02:06	For clarity, buckling is when a component suddenly changes shape or deforms under load, most commonly flexing or bowing under compression.
02:15	Fibreglass and Kevlar composites, which we'll discuss next, are much more flexible than carbon and it also makes them more susceptible to buckling.
02:24	As you'd expect though, it's considerably more expensive than fibreglass and this really comes down to the manufacturing process that we just discussed.
02:31	As stiff as carbon fibre composites are though, they do have relatively poor toughness.
02:38	This isn't generally an issue for motorsport though, as we almost always want to stay in the elastic or temporary deformation area of the stress strain plot.
02:47	There are a few other considerations that are worth mentioning as well.
02:51	One being that carbon fibre is conductive.
02:54	This means that if the internal reinforcing fibres are in contact with steel or aluminium, there will be galvanic corrosion.
03:00	And this commonly occurs when dissimilar metals are in contact.
03:05	And in this case, it will result in accelerated corrosion of the steel or aluminium.
03:10	This will only be the case if a hole is drilled through the composite part for a fastener.
03:15	And in this case, we should have a stainless steel or titanium fastener to slow the rate of corrosion.
03:21	This is the same reason why carbon fibre dust is bad for electronics.
03:24	But on top of this, it's also carcinogenic, meaning it can increase the risk of cancer if inhaled or ingested.
03:32	The risks of this can be avoided though, and we'll cover that later in the course.
03:36	The final property worth mentioning about carbon fibre is its impressive heat resistance.
03:41	Although this mostly comes down to the resin used for the matrix, as this will always be able to handle less heat than the carbon fibres themselves.
03:50	With the properties covered, let's discuss the best places to use it on a race car.
03:54	Carbon fibre is ideal for any part where strength and stiffness are key, but having the part lightweight is important enough to justify the extra cost.
04:04	Examples of this are aero components, suspension members or even the entire chassis itself.
04:10	It's also great for lightweight parts subject to high temperatures like brake ducting and intake manifolds.
04:16	Something that we haven't discussed yet is that carbon fibre has some undeniably appealing acidic qualities compared to fibreglass, depending on your taste of course.
04:25	This means it's often used purely for its looks.
04:28	Although carbon fibre is strong, it's not cheap to repair or replace.
04:32	Pair this with its lack of toughness and it's easy to see how it's not worth using this composite for parts that will likely be subject to impact.
04:40	However, with that said, we will be able to repair damaged parts or construct new parts with the skills learned in this course for a lot less expense than taking it to a professional, but that doesn't stop them from fracturing in the first place.
04:54	Let's summarise the key points before moving on.
04:57	Carbon fibre composites involve long, thin carbon fibre reinforcements in a matrix of resin.
05:03	The reinforcement is available in a range of different forms, like non-woven mats, unidirectional and weave fabrics, as well as prepreg.
05:11	The key properties are its great strength and stiffness to weight ratios, as well as the temperature resistance, although this does come at a higher expense than fibreglass.
05:20	And there's also a few considerations to keep in mind around corrosion when used with steel or aluminium, and the risk of the carbon dust damaging electronics as well as being harmful to humans if ingested.