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Understanding carbon fiber repairs

Thursday, September 1, 2016 - 07:00
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Carbon fiber material for car manufacture is popular due to its superior strength and light weight even though it is more costly than metals, such as steel and aluminum, and traditional composite materials. Carbon fiber is made of thin carbon filaments bound together with a plastic polymer resin to form a composite material. The material features a “woven” design that is exposed for use on exterior vehicle components such as door and roof panels, fenders and hoods. Carbon fiber can also be painted and used on exterior or interior surfaces.

While carbon fiber is becoming more prevalent as a substrate in car manufacturing, it is still pretty much relegated to high-end automobile models. The more complicated production techniques and molding requirements for manufacturing carbon fiber parts keep the costs high. Carbon fiber bodies and/or parts can be found on super-expensive race cars and sports cars, and more recently on “less-expensive” models from BMW, Chevrolet Corvette, and Alfa Romeo. As advances in manufacturing technology bring down the costs of using carbon fiber, the material will find wider acceptance in more mainstream vehicles.

Carbon fiber consists of thin carbon filaments bound together with a plastic polymer resin to form a composite material.

According to a report by Lux Research, “Scaling up Carbon Fiber: Roadmap to Automotive Adoption,” carbon-fiber reinforced plastics (CFRPs) “will be poised to gain widespread adoption for automotive lightweighting by 2025, driven by a faster-than-expected pace of technology development.” The report also notes that the adoption of CFRPs is prevalent on whether “they can become affordable enough for use in mainstream vehicles.

Cosmetic vs. Structural Repairs
It is important to understand the difference between a cosmetic and a structural repair. Most of the repairs will be structural repairs to the cosmetic panels, such as mending a hole in a carbon-fiber panel. Although the cosmetic carbon-fiber panels add some strength to the car, they are not structural to the integrity of the whole vehicle. The majority of the carbon-fiber panels in use now are mechanically fastened to the car, although there are some panels, such as Tesla’s, that are bonded to the base structure.

As for choosing the proper adhesive for making a repair – bonding will be done with a urethane or epoxy adhesive, while repair work is always done with an epoxy. The decision centers on the benefit the repair accomplishes for the life of the vehicle. If the damage to the vehicle requires a cosmetic repair to a structural element, then epoxy is the choice. Epoxies are not flexible and will form a solid attachment; urethanes are too flexible for this type of repair.

A repair is considered to be cosmetic when the carbon fiber is not damaged – such as a surface scratch or pitting to a panel. This basic type of repair involves hiding the imperfection and painting the repaired portion. An epoxy filler can be used to make this repair, since it is as rigid as the panel. When damage has been done directly through the carbon fiber part, such as a hole, the damaged fiber must be replaced with a suitable repair fiber and an epoxy.

Carbon Fiber Repairs
When the actual structure of the vehicle is composed of carbon fiber, repairing damage takes more skill and the repair process is defined by the OEM.  Due to the configuration of the carbon fiber material, repair work must take into account how many layers of carbon fiber are involved, along with what type of carbon fiber cloth needs to be installed and at what orientation.

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