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A guide to Carbon Fiber Reinforced Polymer repairs

Thursday, December 1, 2016 - 09:00
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Carbon fiber material for car design is becoming more and more popular with OEMs due to its superior strength and being light weight. Everything in life is a trade-off and although Carbon Fiber Reinforced Polymer (CFRP), or carbon-fiber laminates, is costlier than steel or aluminum, or traditional composite materials, carbon laminate is the next-generation material for making cars lighter, more fuel efficient and safer.  Carbon laminate is extremely strong and stiff because of its woven layers of nearly pure carbon fibers bonded together by a hardened plastic, such as epoxy resin.  CFRP is combination of thin carbon filaments bond together with a plastic polymer resin to form a composite material.  Because the fibers are entirely carbon, their density is only about 1.6 grams per cubic centimeter (g/cc), comparable to the density of table sugar, resulting in carbon laminates with densities of around 1.3 to 1.5 g/cc.

2016 BMW 7 Series (G12) Body-in-white CFRP, aluminum and HSS and AHSS
2016 BMW 7 Series (G12) CFRP B-pillar inner reinforcement

However, the carbon laminate manufacturing process is complex and requires either manual labor or expensive robotic machines, both of which result in high costs for the finished part. And, the most commonly used polymer (epoxy resin) requires 24 to 50 hours to solidify after it's infused into the carbon fiber, further increasing costs.  In contrast, the density of steel is about 7.8 g/cc.  Carbon fibers are slightly stiffer than steel, but have one-fifth the weight.  Carbon laminate density is so low, it even beats the lightest structural metal, magnesium, which has a density of 1.8 g/cc.

Visually, CFRP has a woven or weaved design look that is exposed, you have probably seen it many times on vehicle components, such as roof panels, fenders and hoods.  Most likely what you saw was wraps of “Carbon Fiber Look” material on a fiberglass or composite panel on inexpensive vehicles.  CFRP components are very expensive and very light weight.  Generally, you will see CFRP components on high-end luxury vehicles, high-end muscle cars and sports cars and super cars.

2016 BMW 7 Series (G12) inner quarter reinforcement CFRP (left) and upper roof rail and front header reinforcements CFRP (right)

Now keep in mind some OEMs will refinish CFRP components used for exterior and/or interior components.  Manufacturing vehicles like the McLaren 570S or SLR with an entirely composite structure is a massive undertaking.  In 1981 the world was introduced to the first Formula 1 carbon-laminate car.  As the years passed the technology transitioned to only a select few low production high-end models.  Despite intense research and development efforts over the past 35 years we are just starting to see carbon fiber laminate in vehicles under $50,000.  Some of the most complex challenges are producing carbon laminates in complex shapes, ensuring uniform penetration of the epoxy throughout the parts, taking into account the differing strength properties when the material is struck from different angles (strength is better in the direction of the fibers) and ensuring quality control.  Overcoming these challenges is expensive, so carbon-laminate composites are only used extensively in models that are entirely performance-oriented, including the Alfa Romeo 4C, the new Ford GT and the hybrid Porsche 918. 

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