Grades of Carbon Fiber

What’s the different between 1K, 3K, 12K and UD (Uni-Directional Carbon) carbon fiber?

Fibers are bundled in various sizes designated in thousands (K) of fibers. This is made by weaving bundles of carbon filaments called ‘tows’. These tows are commonly made up of 1,000, 3,000 or 12,000 individual carbon fibers—these are referred to as 1k, 3k 12k etc. There are many different styles of weave that give different properties and looks.These fibers are woven into fabric with various width sizes. A 1K weave will be approximately 1mm in width while a 12K weave will be much larger at approximately 12mm and so forth. The various types of fiber will have the same “K” designation to indicate the number of fibers in the bundle.

The outer layer of any carbon frame serves several purposes. The first purpose is to provide a cosmetic layer of carbon giving the frame it’s final look. Secondly, it provides a final touch to the ride of the bicycle. Some weaves are more rigid than others and some weaves flex more providing more supple ride characteristics.

Advantages of woven carbon fabric
A woven fabric contains fibers oriented on at least two axes, in order to provide great all-around strength and stiffness. A sheet of woven fabric once cured can take flexural and tensile loads on multiple axes, and even exhibits good stiffness properties off axis. The real benefits of woven materials, however, come from their behavior in less than ideal circumstances, such as when punctured or exposed to bearing loads.

A carbon strand is strongest when straight, and therefore loses some of its theoretical strength when it is bent around other fibers to produce a weave, but if a strand is broken or punctured in a weave, the surrounding fibers, because of this bend, behave as if unbroken. Therefore, if a hole is punched in a weave, strands punctured in one place, will behave at full strength within a very short distance (typically one to two weave widths) from the damage.

With a unidirectional fabric, a fiber puncture will compromise strength for the entire length of the fiber, relying on the resin strength (or sandwiched woven fibers) to distribute loading across the broken fibers. These same properties also result in better toughness, and impact strength than uni-directional material. However for the equivalent strength the woven carbon is 1.4 times heavier unidirectional carbon.

1K Weave – It is lighter than other fibers and provides a more supple ride than a larger weave.

3K Weave – It provides a comfortable ride while still allowing the bike to be stiff and strong enough to handle a powerful rider in the midst of his/her best sprint.

12K Weave – 12K is the largest weave and the stiffest. It is slightly heavier and much less expensive to use in production.

Uni-Directional Carbon – Unidirectional has the fibers running in one direction only and doesn’t have the same woven look.

Know the modulus of carbon fiber
The ‘HM’ designation (High Modulus) refers to the tensile strength in tonnes per square centimeter. 46HM refers to a tensile strength of 46 tonnes per square centimeter. High Modulus fiber has a tensile modulus of 55 MSI (Million pounds per Square Inch) and higher. Tensile modulus is a measure of how much pulling force a certain diameter fiber can exert without breaking. Therefore High Modulus carbon fiber use less material to get the same stiffness and therefore a lighter structure.

High Modulus Carbon Fiber Smaller fiber and denser = lighter and stronger (Higher tensile strength)

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