An Easy to Digest Guide to Carbon Fibre
Carbon fibre comes in a wide variety of variable formats, and it is important to understand each of its forms before using it commercially, or at home for your DIY or repair projects.
There are a number of factors which can even differentiate each different kind of carbon fibre cloth; their weave, their weight, the way they are treated during production, and so on.
In this article we will be exploring the various attributes which set one form of carbon fibre apart from another.
Common Carbon Fibre Cloth Types, Tow Sizes, Weight, and Weave
The types of carbon fibre available are named by their respective patent holders, so the type usually also represents a particular brand, or model number.
Each type has different variables which include tensile strength, modulus, and elongation, or strain.
Tensile strength, simply put, is how hard it is to break the carbon fibre by pulling it apart by end to end. A higher tensile strength means it is much more difficult to break than that of a lower tensile strength.
Modulus is how stiff the fibre is, and a higher modulus means that the carbon fibres are stiffer. Here’s the somewhat tricky part; the more stiff, or, the more modulus the carbon fibre, the less tensile it will be. Therefore a low or standard modulus has greater tensile strength than that of a high modulus carbon fibre.
The elongation or strain of carbon fibre refers to how much the fibre, or cloth, can stretch. A low modulus, or, a less stiff carbon fibre can stretch more than a higher modulus carbon fibre.
Simply put, it’s sort of like anything else when it gets cold. The colder something gets, the weaker and more brittle it can become. Colder objects can’t stretch as well as they can when they are warm, and a similar logic applies to carbon fibre.
A “tow size” for carbon fibre simply refers to the number of filament fibres in a bundle. So for example, T700 – 12k, a common type of carbon fibre, has 12,000 filament fibres to a bundle.
The filament of carbon fibre is thinner than a human hair, and when bundled together they form the tow. The tow is used to create carbon fibre cloth.
And of course, there are also many variations of tow sizes, however, the most common sizes are 3k, 6k, and 12k. Just like thick rope, the more individual filaments in the tow, the harder it is to wrap it around corners or bend it.
Often distributors of carbon fibre fail to mention the brand and/or type of carbon fibre used to make carbon fibre cloth, so don’t be afraid to ask.
Pretty straight forward; the weight refers to the weight of the carbon fibre cloth per yard.
It is usually cheaper to buy a single carbon fibre cloth with more tow (heavier), than to buy multiple cloths with less tow (lighter).
Carbon fibre cloths “weave” refers to how the tow is woven into the cloth.
There are a good many types of weaves available on the market, however, the most common ones are twill, satin, plain, uni-directional, and triaxial.
The more over-and-under wrapping in the weave, the weaker it will become. In practice, the corporeal property of the plain weave will be weaker than the satin weave.
The reason for this is due to the tow preventing each fibre from straightening out when stretched; it’s too dense.
The less grooved, bumpy, or overlapping the carbon fibre cloth, the stronger it is.
Here is where the funny words come out; “Prepreg” is short for “pre-impregnated” cloth. Whether the cloth is carbon fibre, Kevlar, fibre glass – you name it — is either pre-wetted with wet or dry epoxy.
Wet prepreg has had epoxy poured and spread over it, which later hardens. Dry prepreg has as well. However, the dry prepreg epoxy remains somewhat sticky in room temperature and requires heat to cure it
Cloth Orientation and Direction
Put quite simply; the orientation of the cloth refers to the direction of the weave, much like wood has grain. It is important to understand the orientation of carbon fibre cloth for when you need to cut it, also much like wood.
The direction of the weave is how many different directions it may be flowing; unidirectional carbon fibre goes in one direction, whereas bidirectional, triaxial, and quadaxial respectively are woven in two, three, and four directions.