Carbon Fiber Inside the Engine - How CF rods and pistons change engines and why you can't have them
Let’s say that you want a car part that’s strong. Something that needs to consistently and reliably survive massive forces. How massive, well, let’s say around 100.000 newtons. But how much is a 100.000 newtons…..well to put into perspective an average person like myself can throw a punch with a force of about 1000 newtons. An average sledgehammer blow is around 5.000. So 100.000 newtons is 20 times stronger than a sledgehammer blow. And that's roughly the force to which engine internals are subjected thousands of times per minute when the engine is revving and under load.
To ensure that connecting rods can survive the violent loads inside the engine we usually make them from steel. But sometimes we also make them from aluminum. Now steel is strong. A high grade alloy like 4340 steel can survive a load or stress that is equivalent to nearly 75.000 newtons exerted on every square centimeter of the part before breaking apart. Aluminum isn’t as strong and even high grade alloys like 6061 or 7075 can only manage a maximum of 55.000 newtons per square centimeter. Now carbon fiber is completely is in a league of it’s own….it can survive 250.000 newtons per square centimeter before breaking.
Now here’s the interesting thing we actually put rods from the weakest material here, aluminum, into the most extreme engines out there which generate the highest loads and have the highest chances of destroying their internals. Why? Well that’s because aluminum is lighter than steel.
But aluminum plays a price for it’s low weight and the price is longevity. So with metals we have to compromise, we can either have low weight OR long life, we can’t have both. Now let’s look at carbon fiber again. Just like it blows steel out of the water in terms of strength it blows aluminum out of the water in terms of weight.
So carbon fiber is the absolute champ? It’s super strong, it’s super light and it has no real fatigue life issues. So if it’s the best material out there why are there zero mass produced engines with carbon fiber internals and zero aftermarket carbon fiber rods you can purchase today? I mean we make wheels, car chassis, spoilers and so many other things from it. Why not engine internals if they offer so many benefits?
Here’s the first issue. Carbon fiber does not exhibit isotropic properties. When a material is isotropic it exhibits pretty much the same mechanical and thermal properties in all its parts.
For example this block made from steel is equally strong everywhere. Applying the load here or here will have the same results in terms of the amount of force required to deform or break the block. But carbon isn’t like this. Carbon fiber isn’t isotropic, it’s orthotropic in other words it’s a bit like a wood. Parts made from carbon fiber can’t be one solid chunk as is the case with metals.
Another major problem is the manufacturing process. If you wish to make strong carbon fiber parts you really have only two options. Using dry carbon fiber layers and then bonding them manually together by brushing or rolling resin onto them or by using prepreg. Advanced manufacturing process than involve an autoclave which exposes the part to both high pressure and high temperatures during the curing process to ensure the best possible part uniformity and surface finish.
And as you can see this process of manual stacking of layers, long curing times and the high cost of the raw material itself explains why carbon fiber parts are so expensive. Another issue is that this type of manufacturing process can be very difficult to apply on parts with complex and intricate shapes.
But in 2010 at the Paris Motor Show Lamborghini unveiled something called the Sesto Elemento, a striking limited production run race car. It’s name means “the sixth element”, which is the atomic number of carbon and indeed the car’s chassis, body, drive shaft and suspension components are all made from carbon fiber, but it wasn’t the first to have so many parts made from carbon fiber, instead it was the first to feature something called Forged composites. A brand new unique "forged "carbon fiber manufacturing process which was employed in the tub and suspension arms of the car.
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#d4a #carbonfiber
00:00 Carbon fiber vs steel vs aluminum
10:29 "Forged" carbon fiber
16:46 I contacted Lamborghini and other pioneers
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