Carbon fiber was first developed by Union Carbide in the late 1950s when they created a high-performance fiber for aerospace applications. But the real breakthrough came in 1963, when British scientists at the Royal Aircraft Establishment discovered a new manufacturing process that improved fiber strength and stiffness. Japanese researcher Dr. Akio Shindo refined this process even further in the 1970s, leading to the modern carbon fiber we use today.
At its core, carbon fiber is made of thin, crystalline filaments of carbon atoms bonded together in long molecular chains. These filaments, typically 5-10 micrometers in diameter, are bundled together to form threads (known as tows), which are then woven into fabric. The base material or precursor is usually polyacrylonitrile (PAN), though some fibers are made from petroleum pitch or rayon.
How Carbon Fiber is Manufactured
Raw Material Production
These PAN fibers are washed and stretched until they reach the desired fiber diameter. This aligns the molecules within the fiber and creates tightly bonded carbon crystals. The fibers are heated to 400-600F in a process that adds oxygen molecules and rearranges the atomic bonding pattern from a linear pattern to a more thermally stable ladder bonding. Afterward, the fibers are heated to 2,000-5,500F in an oxygen free environment to expel non-carbon atoms from the material. As non-carbon atoms are removed, the remaining pure carbon atoms form long chain tightly bonded crystals that are parallel to the long axis of the fiber. This is what gives carbon fiber its unusual strength properties.
Material and Fabric Production
Next, the fibers are collected into bundles called “tows” and wound onto bobbins. Standard tow sizes are 1k, 3k, 6k, and 12k, although some specialty products use tows that are 48k and higher. The K indicates the “thousands of filaments per tow”– for example, a 3k bobbin has 3,000 carbon fiber filaments per tow and the 6k has 6,000 filaments per tow. All of those tiny filaments gathered together in a carbon fiber strand create a tow with amazing strength.
Once the tows are on bobbins, they’re sold to fabric weavers who weave it into various types of carbon fiber fabric. Most common are plain weave, 2×2 twill (called 2 by 2 twill) and harness satin. Still other options include unidirectional, multidirectional (biaxial, triaxial and quasi-isotropic). There’s also nonwoven carbon fiber in the form of chopped or continuous strand mats. (In fact, our Protech marble carbon fiber is also a non-woven product.) This dry carbon fiber fabric is shipped to distributors and manufacturers and will be infused with resin at their facilities.
Prepreg Fabric Production
Another type of carbon fiber fabric is prepreg. This is carbon fiber fabric which is coated with resin in a secondary manufacturing process making the fabric “pre-impregnated” with resin. The result is a fabric that feels a little waxy or sticky to the touch. Prepreg’s greatest advantage is its simplicity as the resin is already applied to the fabric and requires only heat to cure.
Carbon fiber sheets can be made easily by stacking up layers of prepreg fabric in a hot press. Molded products can be shaped and cured in an oven or autoclave without additional resin infusion. On the downside, prepreg is more expensive, must be shipped and stored under refrigeration and has an expiration or “use by” date. Outdated prepreg tends to dry out over time and the resin loses its ability to melt and cure adequately.
Carbon Fiber Sheet Production Methods
There are three main ways to manufacture a carbon fiber sheet – wet layup, infusion or hot press/Autoclave. Each one has its own advantages and disadvantages:
- Wet Layup
Resin is spread manually over carbon fiber fabric and left to cure.
→ Advantages: Simple to do, minimal materials required, lower cost
→ Disadvantages: Messy production process, final product is resin rich, difficult to get uniform resin coverage, not suitable to create thick sheets, pinholes can be an issue - Vacuum Infusion
Resin is infused into carbon fiber fabric using vacuum and pressure.
→ Advantages: Ability to regulate the amount of resin infusion into fabric, lower likelihood of pinholes
→ Disadvantages: Experience and skill required. Higher cost due to materials required to support the infusion process - Hot Press/Autoclave
Prepreg carbon fiber is loaded into a heated press or mold. Very high pressure and heat is applied which liquifies and cures the resin embedded in the fabric.
→ Advantages: Manufacturing process is simple and clean. No need to work with resin as it’s already part of the fabric. Limited skill required. Overall lower fabrication cost than vacuum infusion. Minimal voids or pinholes. Generally produces high quality parts
→ Disadvantages: Initial cost and space requirements for press or autoclave. Restrictions on maximum part dimension (depending on equipment)
Carbon Fiber’s Strengths and Weaknesses
Carbon fiber offers exceptional performance in a number of applications but it’s not always the best or most cost-effective choice for others. Here’s a quick breakdown of the best attributes and the challenges of working with carbon fiber:
Strengths
- Exceptional strength-to-weight ratio (5x stronger than steel and half the weight of aluminum)
- High stiffness and dimensional stability
- Excellent fatigue resistance
- Low thermal expansion
- Good chemical resistance
- Electrical conductivity
- Thermal conductivity
- Can be molded into complex shapes
- Excellent cosmetic attributes
Weaknesses
- Higher cost than alternative materials
- Not as impact resistant compared to metals
- Difficult to repair
- Typically not UV resistant (although this can be easily added with a special coating)
- Its strength varies by fabric weave, layup and direction
- Potential galvanic corrosion when in contact with metals
Optimal Applications
Carbon fiber truly shines in applications where its exceptional strength-to-weight ratio can be used to its full advantage. The following are examples of industries that have tapped into its unique benefits:
- In the aerospace industry, it has revolutionized aircraft design, enabling the construction of lighter, more fuel-efficient aircraft while maintaining structural integrity.
- The automotive sector, particularly in high-performance vehicles, has embraced carbon fiber for components for its appearance and its ability to create lighter, faster cars with body panels and chassis elements that are lighter and stronger than their metallic
counterparts. - The sporting goods industry has perhaps made carbon fiber most visible to the general public. Professional sports equipment manufacturers have leveraged its properties to create superior tennis rackets, golf clubs, and bicycle frames that offer enhanced performance through improved stiffness and reduced weight.
- In the industrial sector, carbon fiber has found its place in equipment requiring high stiffness and dimensional stability, such as robotic arms and precision machinery components.
- Medical technology has also benefited significantly from carbon fiber’s unique properties. Prosthetic limbs made from carbon fiber composites provide patients with lightweight, durable solutions that can better mimic natural movement. Its radiolucent qualities (transparency to X-rays and radiation) makes carbon fiber a go-to material for use in X-ray and imaging technology.
- Its success in wind turbine blades clearly demonstrates its value in renewable energy applications, where its combination of strength, lightness, and fatigue resistance allows for larger, more efficient turbine designs.
Still, carbon fiber isn’t the ideal choice for every application. In situations where impacts are frequent or severe, carbon fiber’s highly brittle nature and potential to break on impact can be a deal-breaker for some products. Low priced or cost-sensitive products are less likely to be a fit due to carbon fiber’s premium price.
Products that need repair are another challenge as carbon fiber composites are inherently more difficult and expensive to repair compared to other materials. And while carbon fiber’s conductivity can be an asset, it’s problematic in applications where electrical insulation is crucial.
Determining the ROI of Carbon Fiber For Your Application
Carbon fiber is one of engineering’s most sophisticated material solutions. It offers exceptional performance advantages over other materials that make it the material of choice for some applications. Still, it’s important to understand its characteristics and limitations when determining its best use.
If you’re considering using carbon fiber in your application, it’s important to clearly assess your performance requirements. You’ll want to consider not only mechanical loads, but environmental conditions, service life needs, and any potential impact scenarios that challenge the integrity of the part. Temperature ranges and chemical exposure should also be factored in as they can affect long-term performance.
If your evaluation suggests that carbon fiber is the right fit, the next step is to determine the best and most cost-effective product to meet your needs. See our blog post “Understanding Carbon Fiber Pricing — Where You Can Cut Costs and Where You Shouldn’t” for a deep dive into cost
factors.
While the initial investment in carbon fiber often exceeds that of traditional materials, the performance benefits can deliver substantial long-term value in the right applications. The key lies in understanding what benefits carbon fiber brings to your application and whether the economics pencil out.
Beyond the material costs, your return on investment should also be part of the equation. For some applications, carbon fiber brings unique benefits and strategic advantages that make it well worth the added investment.
If you’re interested in exploring how carbon fiber could be used in your application, feel free to contact us anytime We’ll help you assess whether it’s the right fit for your specifications and put together an approach that fits your needs — including a range of cost alternatives in carbon fiber products and explain what’s appropriate for your application. For example, using hybrid fabrics (a combination of carbon fiber and fiberglass or other products) is one possible way to balance performance and lower costs.