What you need to know about repairing carbon fiber

by Douglas Craig, Technical Application Engineer & Collision Industry Liaison, Structural Adhesives Tech Service, LORD Corporation

Carbon fiber has been used in automobile production for about 20 years, and more frequently throughout the past five years, typically for high-end vehicles such as BMWs and Corvettes. Carbon fiber is composed of thin carbon filaments that are bound together with a plastic polymer resin to form a composite material. The fibers are woven into a complex weave that is both strong and lightweight. Carbon fiber does not contain any metal elements.

Douglas CraigMost collision shops will be making structural repairs to cosmetic carbon fiber panels. The repair shop technician will be fixing the outer skin of a vehicle – a ready-to-repair type of damage – such as a scratch on the surface of a hood or a small hole in a door panel.

As an example, if a Corvette has a visible carbon roof that is scratched, a repair can be made if the roof will be painted. With a light cosmetic scratch, the panel can be clear-coated to hide the scratch. But if the carbon fibers are torn, a repair patch would be visible and not acceptable to the customer. For replacement procedures, a mechanically fastened or bonded carbon fiber component can be replaced in the shop.

The decision to repair or replace a carbon fiber component is the same as with any metal or composite component – analyze the damage and estimate the time it will take for repair vs. the cost of a part replacement. For instance, if there is damage to a carbon fiber hood on a Shelby Mustang, a technician can spend several days recreating the hood, painting it and getting it ready for the customer. If it makes good business sense to repair the hood, rather than spend $15,000 on a new hood, then that would be the best decision. If you can do the repair, that is the key, and the answer to “repair vs. replace.”

Visibility of a repair is another factor that enters into the decision-making process for repair vs. replace. If the carbon fiber component is painted on the outside surface and the backside of the repair will not be visible, the repair can be made and should be acceptable to the customer. A visible repair would probably not be considered satisfactory.

For example, a repair made to a carbon fiber hood on a Corvette might look good from the outside after it is painted, but if you can see the patch on the underside of the hood when you open the hood, this might not be acceptable to the customer. Corvette owners want their vehicles to look good both outside and inside, so in this instance, a replacement would be preferable.

There are no special tools, equipment, product, or training required for repairing or replacing of a carbon fiber component. Any of the products that are currently used to repair fiber-reinforced plastics and fiberglass can be used for cosmetic repair of body panels, hoods, decks, and doors.

Some of these products include heat-set plastic panel repair adhesives, flexible and rigid foams, plastic bonding adhesives, and plastic-to-metal bonding adhesives. Consult your repair product supplier for information on which products are suitable for repairing carbon fiber parts. Your supplier will also have instruction sheets with preparation, application and finishing techniques for carbon fiber repairs.

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