The entire monocoque tub on...
The entire monocoque tub on an Indy car is made of carbon-fiber cloth, Kevlar cloth, aluminum honeycomb, and resin. This provides a strong, stiff chassis that will absorb crash-impact forces while protecting the driver.
Tell anyone you have a part made with carbon fiber and you'll probably get an impressed "ohhhh" in reply. Why? Because carbon fiber is a high-tech product that is lightweight but strong and stiff-perfect for building chassis, structural components, and more. If you have ever wondered what it takes to make carbon fiber parts, here's your chance to learn about the materials, the processes, and the uses for it.
What Is It?
When someone says a part is made of carbon fiber, that really is a gross oversimplification. Any carbon-fiber part is actually a composite of many components. To get the carbon-fiber cloth to set in a shape and/or adhere to a section of honeycomb to use as a structural component, various types of epoxy resin are applied to the cloth. The resin and structural additions, which would include the honeycomb section, metal stiffeners, and more, are covered by the carbon-fiber cloth, which is why these components are simply called carbon fiber.
The core material for parts...
The core material for parts that are used in structural applications, like a chassis, wing strut, or something similar, consists of a honeycomb with a "skin," usually carbon, Kevlar, or a combination of the two. The part standing has a bare piece of aluminum honeycomb, while the part lying down has a carbon skin bonded to it.
There is a plethora of carbon cloth, resins, and structural components to choose from when making a composite carbon-fiber piece. The choices for each depend on certain parameters, such as the type of usage the part will see (structural, aerodynamic, or for appearance), how light the part needs to be, how difficult the part is to manufacture, how much the customer is willing to pay, and whether using carbon fiber is legal in the type of racing for which the component is being built.
The types of cloth available are woven carbon, bidirectional carbon, 2x2 twill carbon, Kevlar cloth, hybrid-carbon Kevlar cloth, and woven-glass cloth (also called fiberglass). The carbon cloths have more strength than the Kevlar and glass but cost considerably more. The Kevlar and Kevlar-carbon cloth is less brittle than the carbon, so it is used in crush zones on a race car to absorb some of the force of an impact. The 'glass cloth is less expensive than the carbon and Kevlar cloth, has less stiffness and strength, and weighs more but is still an excellent choice for many nonstructural components.
Different component uses require...
Different component uses require different cloths. This rack contains, from top to bottom, 2x2 twill carbon, bidirectional carbon, Kevlar, hybrid-carbon Kevlar, and woven-glass cloth to accommodate all needs.
The structure added to a composite can be anything from titanium, Nomex, and aluminum honeycomb to pvc, paper (cardboard), or solid pieces of metal. The honeycomb is used in aircraft and race cars, like the IRL cars, to add strength to a part but keep the weight to a minimum. The many styles of honeycomb include alumi-core (honeycomb made of aluminum), standard Nomex-core (relatively stiff in its raw form but lightweight and heat-resistant), and overexpanded Nomex-hex (has excellent "drapeability" for making complex shapes).
The resin used to give the cloth its shape and/or bond to a structure can be anything from a room-curing epoxy, a high-temperature-curing epoxy, a vinylester resin and a high-temperature vinylester resin to a polyester resin. The polyester resin is not used with the carbon fiber, but everything else can be used. The resins are made of two parts that, when combined, react and cure to a solid form. Most professional composite manufacturers use gloves, breathing protection, and eye protection when working with the resins and cloth to prevent any injury-you should do the same. The high-temperature resins are used in places like engine compartments, but they are affected by temperatures higher than 400 degrees F. For this reason, heat shielding is a must in engine compartments.
There is a carbon cloth called pre-preg that has the resin impregnated in it. To prevent the resin from hardening, the pre-preg is usually stored in the freezer, and while it is out of the freezer it is closely monitored to prevent it from becoming too hard. When pre-preg is used to make a part, it shortens the set-up time considerably. If pre-preg is going to be bonded to a honeycomb structure, some resin needs to be applied to the mating surface of the pre-preg and honeycomb, since there is only just enough resin in the pre-preg to bond the carbon fibers together. Pre-preg is a great way to reduce the cost of making a part by shortening the set-up time, and usually it can be cured at a higher temperature and in a shorter amount of time than standard "wet layup" method carbon-fiber composites.
A close-up of the honeycomb...
A close-up of the honeycomb core material shows how it provides strength while weighing hardly anything at all. The honeycomb on the right is called "over-expanded Nomex hex" and is great for making parts that are not flat because it can be easily shaped. The pieces in the middle and right are different thicknesses of aluminum honeycomb core, which is relatively rigid and often used in monocoques to add strength and for crash resistance.
The cloth needed is laid out...
The cloth needed is laid out on a table and cut to fit the need. Notice the gloves. Carbon or any cloth made of brittle fibers should be handled with gloves, as those little shards can make for a painful experience.
Lying on the table is standard...
Lying on the table is standard Nomex honeycomb, and the flexibility of over-expanded Nomex-hex honeycomb is shown. The standard honeycomb would break if you tried to do this with it.