When synthesized correctly, carbon fiber can be 10x as strong as steel. How strong is carbon fiber in its base form, though, and how can you maximize its strength? We’ll answer these questions and more in this post!
- How do you make strong carbon fiber?
- Why is carbon fiber so strong?
- Does carbon fiber break easily?
- Is carbon fiber stronger than KEVLAR®?
- Can you burn carbon fiber?
- Can carbon fiber rust?
- How strong is carbon fiber filament?
How Do You Make Strong Carbon Fiber?
First, a sheet of fiber and other polymers is heated to a very high temperature in a space free of oxygen. Since there is no oxygen, the fiber cannot burn but instead gets so hot that carbon atoms are all that remain.
Next, the carbon is stabilized and carbonized. This involves heating the burn-resistant carbon to high temperatures in the open air, then putting it into a furnace filled with chemical gases (but not oxygen) and cooking it even further.
Third, the sheet is cooled and immersed in various chemical gases, including oxygen, to give it better bonding properties.
Finally, an epoxy resin coating is applied to the sheet to protect the fibers from damage when used to make products. The composition of the coating varies based on the initial materials used for the fiber.
This is the process to make a single carbon fiber sheet, which is an extremely strong building material but can still be fragile and easy to break in some respects. For more info on how carbon fiber sheets become nearly unbreakable, see the section below on “Does Carbon Fiber Break Easily?”
It’s important to know that making strong carbon fiber is an extremely complex process that definitely can’t be done at home.
Watch this video to zoom in on carbon fiber to see just how strong and closely-knit the carbon fiber strands become.
Why Is Carbon Fiber So Strong?
Carbon fiber is among the strongest materials on earth due to the chainlike bonds of its molecules. This structure is created during all of the chemical reactions and extreme temperature changes the fiber goes through while being made.
The processes bind together thousands of small strands and mix them with an epoxy. Those strands form a layer of carbon fiber, the strength of which is affected by the precise orientation of the strands and the types of fabric used in the layer.
A single layer of carbon fiber is typically around 0.25mm thick, and is not very strong at all. In fact, at that thickness, carbon fiber is very easy to break. That may be counterintuitive to what you know about carbon fiber being strong, but the strength is created in the process of stacking multiple layers as well using the orientation and weave of the fibers, also known as the “layup.”
The molecular purity of carbon fiber also helps it to develop a tightly bonded structure.
Does Carbon Fiber Break Easily?
The short answer is that it can, as described above. The great thing about carbon fiber is you can control the strength and direction of the strength. For example, if you want it to be super strong in one direction, and more flexible in the other, you can do that using a specific type of fabric and layup.
To explain, imagine one of those wooden mats used to make sushi. The mat is made from a bunch of narrow wooden rods that run parallel to each other and are bound together. The result is that it’s easy to bend the mat if you bend against the grain. If you bend with the grain, however, the mat will not bend easily at all because that would mean actually bending hard enough to snap the wooden rods.
Carbon fiber sheets are composed of a series of parallel rods, similar to the sushi mat. But in carbon fiber, the rods are made from treated fiber and are much stronger than wood. Because of this, it’s quite difficult to break a sheet of carbon fiber if you apply pressure in the same direction as the rods. One sheet of rods running in one direction is similar to a type of carbon fiber fabric called “unidirectional,” where all of the fibers run in the same direction..
Now imagine you glue two sushi mats one on top of the other, with the wooden rods of the bottom mat going one way and the rods of the top mat running the other way. Now, the mats support each other and keep each other from bending in either direction.
With unidirectional carbon fiber, as you stack the layers of material, you can control the direction of the strength with each layer. This control of strength direction is one of the benefits of carbon fiber. Utilizing multiple layers, you can make the end product as strong as you need for the given application.
In woven sheets of carbon fiber, the filaments are woven together like the strands of a basket to hold together better. There are lots of different types of weaves which are used for a number of different reasons. It could be aesthetic, or it could be easier to work a particular type of material into a mold, and/or it could have more strength in multiple directions. The types of fabric being used and the orientation they are placed to control the strength, are all part of developing the layup strategy.
No matter what type of weave, though, a single sheet of woven fiber will still be quite weak unless they are layered.
Stacks of carbon fiber sheeting (either woven or unidirectional) with alternating orientations are extremely strong -- up to 18x the strength of steel, in fact.
Watch this video to see how Carbon Fiber is made to be so strong:
Is Carbon Fiber Stronger Than KEVLAR®?
Carbon fiber and aramid fiber (KEVLAR® is simply a brand of aramid fiber) are about equal in strength, although each has its advantages and disadvantages.
First, understand that both materials comprise lots of thin sheets of their respective fabrics, and only achieve real strength when they are thickened up using multiple layers of woven fiber.
Even when many layers are woven together, carbon fiber is very thin and light. It is also extremely strong, but it has trouble standing up to sharp objects like knives.
KEVLAR®, on the other hand, is thicker than carbon fiber, and it is harder to penetrate. Because it is thicker, though, it is heavier and less flexible. It is also much less resistant to heat than carbon fiber.
Can You Burn Carbon Fiber?
You’d have a tough time burning carbon fiber.
If you heat it up to 750 degrees, it will burn very slowly as long as a burning fuel source is applied to it. But even at that point, the burning will stop as soon as the fuel source is removed.
That limited burning is caused by the resin combined with the carbon in the fiber, because carbon itself will not burn. The only reason the fiber burns is because the non-carbon components in it will burn.
There are different types of resin that can support different varieties of heat. A typical epoxy resin is good up to around 200 degrees Fahrenheit, but a high-heat resin will usually resist heat up to 400 degrees. Always check the specifications of the resin being used.
Because carbon fiber is so heat resistant but still so strong, it is used in many engineering applications like the siding inside engines.
Can Carbon Fiber Rust?
No. The tight bonds in the carbon fiber are immune to oxidation because of the complex chemical processes used during manufacturing. The epoxy resins used to protect the carbon fiber from damage are inert, meaning it is safe from rust and other corrosion types.
How Strong Is Carbon Fiber Filament?
A carbon fiber filament is the individual string used on a carbon fiber fabric. Those strands are typically bonded together using a resin, which is the RP in CFRP (carbon fiber reinforced plastic). By pairing the material used to the carbon fiber's exact chemical composition, engineers can create something even more durable, strong, and lightweight than its parts.
In a woven fabric, each strand of carbon fiber will normally have somewhere between 1,000 and 12,000 individual filaments, less than the breadth of a human hair.
So how strong is carbon fiber? Let’s just put it this way: there aren’t many materials in the world stronger than carbon fiber -- especially not commercially available ones.
Want to see the strength of carbon fiber in action? Check out this video!