About Carbon Fiber

Carbon fiber is a super strong material that's also extremely lightweight. Engineers and designers love it because it's five times as strong as steel, two times as stiff, yet weighs about two-thirds less. Carbon fiber is basically very thin strands of carbon -- even thinner than human hair. The strands can be twisted together, like yarn. The yarns can be woven together, like cloth. To make carbon fiber take on a permanent shape, it can be laid over a mold, then coated with a stiff resin or plastic (kind of like how you would make something out of paper-mâché by putting newspaper strips over a mold, then adding paste to force it to hold the shape). The most common type of resin used is an epoxy.

Carbon fiber material has a wide range of applications ranging from aerospace, to automobiles, to sporting goods. Carbon fiber is often used in replacement of steel when weight and strength are concerned. Carbon fiber can be formed at various densities in limitless shapes and sizes, allowing it to be custom-formed into any number of composite parts and pieces.

Common uses for carbon fiber are automobile parts, bicycle parts, fishing rods, ski poles, golf clubs, shoe soles, baseball bats, protective cases, and musical instruments. The number one use of carbon fiber is in the aerospace industry. Military fighter planes, helicopters; and commercial planes like the Boeing 787 Dreamliner, and the Airbus A380: are built with as much as 50% carbon fiber.

Besides its superior performance characteristics, carbon is also used for its cosmetic beauty. When used with clear resin, it has an extremely attractive, almost three-dimensional holographic appearance. When other fiber reinforcements are often hidden with paint or gel coat, carbon fiber is intentionally made visible because of its high-tech look.

• High Strength to weight ratio
• Good Rigidity
• Corrosion resistant
• Electrically Conductive
• Fatigue Resistant
• Good tensile strength but Brittle
• Fire Resistance/Not flammable
• High Thermal Conductivity in some forms

• Low coefficient of thermal expansion
• Non poisonous
• Biologically inert
• X-Ray Permeable
• Self Lubricating
• Excellent EMI (Electromagnetic Interference) Shielding Property
• Relatively Expensive
• Requires specialized experience and equipment to use.

There are many factors in determining what type of carbon fiber to use because not all carbon fiber is created equal. There is low modulus, standard modulus, intermediate modulus, and high modulus. Then there are several tow size differences and a ton of different cloth patterns to choose from.

Tensile strength is how hard it is to break the carbon fiber by pulling it apart from end to end. The higher the tensile strength the harder it is to break.

Modulus is how stiff the carbon fiber is: the higher the modulus the stiffer the carbon fiber. Because the higher modulus is stiffer, this also makes it more brittle and weaker. Low modulus fibers stretch more than high modulus fibers before breaking.

A carbon fiber filament is the smallest part of the carbon fiber cloth. The strands are then bundled together to create what's called the "tow." The tow is a bundle of individual fiber filaments or strands that create a larger strand. The tow is then woven together into a cloth or a weave. The most common sizes are 3k, 6k, and 12k. The "k" stands for thousands so there are 3,000 individual filaments in a 3k tow, 6,000 strands in 6k, and so on. If the tow has more filaments, or higher "K", the cloth will be more densely packed making it harder to shape around corners or complex curves.

Cloth weight is usually shown in ounces per yard. Tighter woven cloths using the same type of tow will weigh more than cloths using less tow in the same amount of space. Often times using a heavier cloth in place of a lighter cloth can save on material cost, since it is usually cheaper to buy a heavier cloth than buying a lighter cloth and doubling it.

There are several types of weaves out there; Twill, Satin, Plain, Unidirectional (Uni), triaxial, and so on. What you need to understand about weaves is that the more under and over lapping within the weave the weaker it will be. For example a plain weave will be more prone to breaking than a 4 harness satin weave using the same type of tow. Why? Because as the cloth begins to come under tension the fibers try to straighten out but can't because there is another tow bundle under them restricting them from becoming straight. Therefore, there is a shear force applied to the straightening tow and it snaps. In other words as the tow straightens out it presses on the tow that is running under or over it going the opposite / cross direction. The less overlapping or "bumpy" the weave is over a certain area the stronger it will be. For example a 4 harness satin weave has fewer overlapping bumps than a 2x2 twill weave, which has less overlapping than a plain weave. The strongest cloths are the non woven types like unidirectional cloth because it doesn't experience the shear stress caused by the over and under lapping fiber bundles. It's better in both compression and tension than any other cloth- But it's usually not as pretty.

Imagine you have a roll of cloth that is 35" wide and 100 yards long. The seller will often times tell you the fiber orientation of the cloth. This is important to know in case you need a piece of cloth cut at a certain length. For example if you need a piece of uni cloth that is longer than 35" do you buy the roll with fibers running on the 0 deg, 45 deg, or 90 deg axis?

0 degrees means the tow runs the length of the roll- so in the example above, the fiber will run the length of the roll or 100 yards. So if you needed a piece of cloth over 35" long you would want this roll of cloth.

90 deg means that the tow runs across the roll- so in the example above, the fiber will run the width of the roll or 35" long.

45 deg means that the tow runs 45 deg to the 0 and 90 deg axis. This type of cloth usually is in bi-directional , triaxial, and quadaxial configurations.

Uni or unidirectional cloth has all of its tow bundles running in the same direction with some type of binder holding it together so it doesn't fray or come apart. The binder could be made of several different things including small strands of carbon fiber, fiberglass, Kevlar, epoxy, and etc. Uni cloth is good for projects that required strength in one direction more than the other direction. For example on a longboard you need more strength running length-wise on the board than you do running across the board. Therefore if you used bidirectional cloth for the whole board you would be adding unnecessary weight to the board because you don't need all of the excess material running across the board. So using more uni cloth and less bidirectional cloth adds more strength over the span of the board without adding the extra weight caused by the excessive cross fibers that comes with using the bidirectional cloth.

Bidirectional cloth is the most common and it is usually least expensive. It is great for projects where you need strength in multiple directions. For example bidirectional cloth works well on car hoods, instrument panels, computer cases, and etc. On bikes you will often see bidirectional cloth on the outside of the frame which is usually mostly cosmetic since the other layers are usually unidirectional cloth.

You usually see triaxial cloth on skis and snow boards. It usually has its fibers running in the 0, +45, and -45 dreg fiber orientations. The +45 and -45 deg orientation of the cloth helps strengthen and stiffen the ski and snow boards' torsional flex- In other words it helps to keep the ski or snowboard from twisting.

This cloth is less common but is used when you need strength running in all directions equally across the part. The fiber orientation is usually 0, +45, -45, and 90 deg.

Yes, you can achieve any of these fiber orientations by cutting you cloth appropriately and layering it accordingly. For example you can take unidirectional cloth and by layering it with one layer at 0 deg, another at 90 deg, another at +45 deg, and another at -45 deg, you just created a quadaxial cloth. However, buying a quadaxial cloth is usually cheaper than layering several layers of uni.