Carbon fiber is a material that is getting a lot of press recently. The articles and stories cover how it is light, strong, and used by the aerospace industry. The articles also cover how many vehicle makers are investing a great deal of research into the space-age material. Often the articles mention exotic cars like the Lamborghini Aventador, McLaren P1, the Alfa Romeo 4C, or the BMW i3 and i8. These vehicles have body structures and outer panels that are made of carbon fiber.
The BMW i3 and i8, for example, are going to have exterior panels and almost the entire passenger cell made of carbon fiber. Carbon fiber is not a material that will only be used for body and trim panels, it will often be used anywhere steel and aluminum is commonly used. This material is steadily filtering down from the exotics to the high-end.
So, how much longer before carbon fiber makes its way into the everyday, high-volume vehicles? And, how will the collision repair industry repair these vehicles as they are produced in greater quantities? To start to get some answers you have to start at the beginning.
Carbon Fiber – What is it?
Carbon fiber is a man made filament or fiber that has a high carbon content. The carbon content is typically between 92 - 99% carbon. Which is one of the reasons that carbon fiber has a grayish-black look. It is made into a variety of different cloths, weaves, or chopped fibers. There are also different weights and qualities of carbon fiber that can vary greatly and need to be chosen based upon the requirements of the part. The fibers are then combined with a resin material to make parts. This resin might be vinyl, vinyl-ester, epoxy, or one of many other types of resin.
In the end, carbon fiber is the buzzword for a specific kind of composite that has amazing possibilities now and into the future.
How do I identify damage on carbon fiber?
When approaching a damaged carbon fiber part, one of the most important things to understand is that composites react very differently than steel or aluminum. Damage to carbon fiber that only seams to be a small crack or blemish could travel much further than you think. The telltale dents and buckles, on aluminum or steel panels, used as a red flag during damage analysis no longer exist. Even three-dimensional measuring may not show where all of the damage is on a carbon fiber structure. With carbon fiber, the majority of the damage could be on the backside of the part or in between the individual plies (layers) of carbon fiber.
To properly analyze damage, special tools and testing equipment is available to help find all of the damage within the composite structure. These tools for damage analysis will widely vary in price, from costing only pennies, to tens-of-thousands of dollars. The available tools and equipment for damage analysis include items such as tapping hammers, thermal-imaging cameras, and ultra-sonic testers.
Is carbon fiber repairable?
The answer is: it depends. The question is just as complicated as asking if a steel or aluminum vehicle repairable. Repairing carbon fiber structures is not harder, it’s just different. It requires some new tools, equipment, and skills. Training on how to handle, inspect, and repair this material will be critical for complete and safe repairs.
If the part is a cosmetic, or exterior panel, some vehicle makers allow limited repairs using conventional composite repairs. These repair materials are the same materials that are used for sheet-molded compound (SMC). The same repair techniques are also used, but there is a chance for contour mapping of the repair because the carbon fiber panels are so thin. If the damaged part is a component of the vehicle structure the repair process changes.
What are the options for repairing carbon fiber?
There are several repair options for carbon fiber depending on damage and vehicle maker repair instructions. These include vacuum bagging, adhesive bonding, rivet bonding, and conventional composite repair.
Vacuum bagging is the main focus of the I-CAR Introduction to Carbon Fiber CFR01e course. There are many different options and steps to this repair. With this type of repair, each of the damaged plies is removed and replaced in the area of damage. The repair is then compressed and heated to cure the repair.
Click here for an overview video.
Adhesive bonding is only done at a factory seam of a composite part. It involves removing the damaged part, using partial replacement techniques, and adhesively bonding the seams. This type of repair is only done when there are vehicle maker repair instructions.
Rivet bonding is usually done at a factory seam of the composite part. It involves removing the damaged part and replacing the part with rivets and adhesive. This type of repair is only done when there is a vehicle maker repair procedure.
Conventional composite repair uses the same products and techniques that are used on SMC repairs. This type of repair can only be used for cosmetic applications because these products are weaker than carbon fiber and will not have the same performance standards.
Carbon fiber is relatively new to the automotive industry, but it is repairable depending on the damage. As the collision repair industry starts to repair these vehicles there will be challenges to overcome. The challenges with carbon fiber intensive vehicles are similar to the way that the industry is learning and adapting to unibody construction, high-strength steel (HSS), ultra-high-strength steel UHSS, and aluminum intensive vehicles.
The first step to meet these challenges is to begin to acquire knowledge about the material and what is involved in the repair process with this space age material. The industry will need to identify when to make the investment in tools, material, and training. It is not a question of if carbon fiber is going to appear in high production vehicles, but when it will appear.
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