Carbon Fiber: Definition, Properties, Applications, and Uses in 3D Printing
Carbon fiber is a weaved mat of fibers that when impregnated and cured with resin, creates a material that is lighter and stronger than steel. It is used in high-performance applications in the aerospace, medical, construction, sports, marine, and military industries. Carbon fiber is being developed for use in energy storage systems and already has some use in 3D printing. 3D-printed carbon fiber is incorporated into a part using a different method than traditional carbon fiber but still results in high-strength, low-weight components. The limiting factor of carbon fiber is its high cost. However, its cost is falling, which is opening up carbon fiber for many more applications. This article will discuss: What is carbon fiber?, its properties, applications, and uses in 3D printing.
Carbon fiber is a large number of carbon filaments that are grouped together and weaved into a mat of fabric. The mat of fabric is then cut into shape, built up with multiple layers, and impregnated with resin. The resin is then cured to make a part. Carbon fiber is special because of its impressive strength-to-weight ratio. Figure 1 below is a picture of a wing mirror made out of carbon fiber:
Wing mirror made of carbon fiber.
Image Credit: Shutterstock.com/Composite_Carbonman
Carbon fiber can also be referred to as graphite fiber or carbon graphite. It may be referred to under the umbrella terms composite or fiber-reinforced plastic. The term composite is used to describe a material that has a matrix and reinforcement. In the case of carbon fiber, the fiber is the reinforcement and the resin is the matrix. Fiber-reinforced plastic is used to describe glass fiber and aramid composites as well as carbon fiber.
Carbon fibers were first created in 1860 by Sir Joseph Wilson Swan for use in an incandescent lightbulb as these fibers had a very high heat tolerance. However, carbon fiber filaments at the time were not very strong. So when tungsten started being used in lightbulbs, carbon fiber had no use for over 50 years. Then, in the 1960s, stronger carbon fibers could be produced for use in jet engines by Rolls-Royce. However, due to the brittle properties of carbon fiber, its use was limited for a long time. Since then, carbon fiber production has become much more effective. Carbon fiber today has a tensile strength in the range of 4,000 MPa and a modulus of 400 GPa which has opened up many more applications for its use.
The oxidization, carbonization, and graphitization of the carbon precursor polyacrylonitrile make up 90% of carbon fiber material. The other 10% of precursors used are either from pitch or cellulose.
The non-mechanical properties of carbon fiber are:
- Electrically conductive
- Corrosion resistant
The mechanical properties of carbon fiber include:
- High strength
- Creep resistant
- Fatigue resistant
- High modulus
As with other composites, there are six main weave styles for carbon fiber. The most simple weave is a plain weave which is a one-over-one-under style. The five other weave styles are:
1. Twill weave:
2. Satin weave
3. Basket Weave
4. Leno Weave
5. Mock leno weave
The crimp of each weave affects the material properties. The crimp is the number of times a fiber goes over and under the fibers running perpendicular to it. The generally high crimp results in poor drapability, and strength, but good stability. Drapability is the material’s ability to form complex geometry before curing, and stability is a measure of a weave’s ability to stay together when being laid up for curing. Table 1 below shows the rating of each weave’s properties:
Table 1: Rating of Weave’s Properties
Table Credit: https://composites.ugent.be/
Table 2: Range of Tensile Strength and Modulus Properties of Carbon Fibers
Table Credit: https://composites.ugent.be/
No, carbon fiber is not heavy. Carbon fiber is very lightweight which is one of its two most desired properties, the other being its strength. The weight of carbon fiber will depend on the number of fibers per cm2 and the resin used to bind it. As an example, a plain twill weave of carbon fiber without resin will weigh 210 g/m2, with a thickness of only 0.28 mm. For comparison, steel has a weight of 4 kg/m2 for a thickness of 0.5 mm.
The chemical properties of carbon fiber are:
Usually, the requirement for carbon fiber is limited to high-performance applications due to its cost. A full list of industries in which carbon fiber is used is below:
The aerospace industry is used to describe everything from small drones to commercial airliners and satellites. The most important property of carbon fiber for this industry, as with many, is its weight. The use of lightweight material in the construction of commercial airliners saves companies millions in fuel every year for each aircraft. The use of carbon fiber in aircraft today has reduced the weight of some aircraft by up to 20%. Carbon fiber is mostly used in structures such as the fuselage, empennage, nose cones, and rotor blades. The drawback of using carbon fiber in aircraft is Barely Visible Impact Damage (BVID). BVID is damage that can barely be seen if at all by an unaided eye and is a very common damage type in all composites. This is a significant problem as unseen damage can compromise the safety of a component. Detecting BVID is very hard and requires extensive training and testing.
Carbon fiber is used in a range of sporting equipment to reduce weight while retaining strength. It can be found in tennis rackets, skis, snowboards, bikes, and golf clubs. The sports industry has exploited carbon fiber's light weight to be able to make faster-moving equipment. Because of the reduced weight of a bike using carbon fiber, cyclists are able to cycle much faster than before. The biggest problem with carbon fiber in sporting goods is that it's the most expensive material.
Carbon fiber is used both for X-ray devices and implants in the medical industry. Carbon fiber is used for top boards as part of X-ray equipment as it is radiolucent, meaning X-rays can pass through it easily without interruption. Carbon fiber is used for medical implants as it is wear-resistant, has a high strength-to-weight ratio, and has a comparable elastic modulus to bone. The drawback of using carbon fiber over metal for implants is that, unlike metals, carbon fiber is brittle and is more likely to shatter.
Research is being conducted in the hope of developing carbon fiber structural batteries. This would mean that the structure of a car, for example, could be made out of a carbon fiber cell. This technique would reduce the weight of an electric car, making it much more efficient. The drawback of this system currently is that any impact damage to a vehicle is much more likely to result in a vehicle being written off as the damage would be hard to assess and even harder to repair.
Carbon fiber is being used in civil engineering to build bridges and concrete structures. In civil applications, the light weight of carbon fiber, while preferential, is not the most important factor, but strength is. Carbon fiber is being used to reinforce concrete structures in which steel would usually be used. Depending on the steel and carbon fiber, carbon fiber is 5 to 10 times stronger than steel. Carbon fiber is also being used as part of the load-bearing structures of bridges. The biggest disadvantage of carbon fiber in civil engineering is that it’s much more expensive than the steel it usually replaces.
The biggest uses of composites in the marine industry are in yachts and small boats. For decades, the hulls of yachts and dinghies have been made out of fiberglass because of its light weight and resistance to corrosion. The falling price of carbon fiber is a reason it is now being used in yachts. Carbon fiber is also used to build masts, booms, and keels. The strength, light weight, and fatigue resistance are all advantages being exploited by the marine industry. The big disadvantage of carbon fiber in marine applications is that damage is hard to detect, which causes a massive safety issue.
There are many uses for carbon fiber composites in the military and defense industry. The most notable examples include uses in drones, helicopters, jets, and transport aircraft as well as pilot helmets. The light weight and strength of carbon fiber allow for more fuel-efficient and better-performing aircraft. Pilot helmets are becoming increasingly complex and therefore heavier. Using carbon fiber reduces that weight which removes strain from the pilot. The drawback of using carbon fiber in military aircraft is that damage is extremely difficult to detect and fix.
Carbon fiber can be used in 3D printing either as a continuous fiber layer or it can be printed as chopped strands in the filament of a Fused Deposition Modeling (FDM) printer. To 3D print with a continuous fiber, the printer requires two printheads, one for the plastic filament and one for the carbon fiber. The use of a reinforcement layer can create 3D-printed parts that are lighter and stronger than metals. Carbon fiber can also be embedded within the filament as chopped strands. The use of chopped strands of carbon fiber significantly improves the strength and stiffness of a part without a massive increase in price.
Currently, 3D printing with carbon fiber in the aerospace industry is limited. Using new materials and processes requires an extensive amount of qualification before use in aerospace. However, many aerospace companies are using 3D-printed carbon fiber parts for brackets and specialized tooling. 3D printing is being used to create limited production parts which would otherwise have long lead times. Many repairs and maintenance tasks require specialized tooling which has high costs and long lead times. With 3D-printed carbon fiber, lead times and costs are now being slashed.
The advantage of carbon fiber printed parts is the increased strength when compared to other 3D-printed materials. Most 3D-printed parts are made out of PLA or ABS which are relatively weak, meaning the parts cannot be used for structural purposes. However, with 3D-printed carbon fiber materials, the strength is comparable to that of aluminum. This opens many applications for the use of 3D-printed parts.
Yes, carbon fiber is stronger than steel when comparing their respective strength-to-weight ratios. While both steel and carbon fiber have an elastic modulus of 200 GPa, steel is five times heavier than carbon fiber. This high strength-to-weight ratio is why carbon fiber may be preferential in many applications.
Yes, carbon fiber is much stronger than aluminum. Aluminum can reach up to 570 MPa whereas ultra-high modulus carbon fiber can reach a tensile strength in excess of 5.5 GPa. For more information, see our guide on What is Aluminum.
Both traditional carbon fiber and 3D-printed carbon fiber add strength and are lightweight, but the method of application is very different. Traditionally, carbon fiber is a weaved mat of fibers that have a resin applied and then cured. Traditional carbon fiber is usually made into larger panels and tubular sections but can be made into brackets. 3D-printed carbon fiber is either chopped into micro strands and added to a filament from which it is printed into a part usually with complex geometry or is printed as a singular continuous strand in discrete layers of a 3D-printed part.
This article presented carbon fiber, explained what it is, and discussed its various applications in 3D printing. To learn more about 3D printing carbon fiber, contact a Xometry representative.
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