Carbon Fiber

What is Carbon Fiber?

Carbon fiber is 

Carbon fiber as seen on a bicycle, is known as carbon fiber reinforced plastic (CFRP). CFRP is a composite matrix of carbon fibers and resin where the carbon fibers transfer stress loads throughout the resin structure, similar to steel rebar in reinforced concrete.

Size comparison of a carbon fiber and human hair

Photo: Wikipedia

How are Carbon Fibers made?

Individual carbon fibers are created through the carbonization of polymer filaments such as rayon and polyacrylonitrile (PAN). To carbonize these polymer filaments, they are baked at high temperatures to burn-off all non-carbon atoms, resulting in long molecular chains of pure carbon. Changing the baking temperature and cooling cycle will yield fiber with varying properties.

The finished fibers are 5-10μm (micrometers) in diameter, just a fraction of the thickness of a human hair (17-180μm).

Sources: Protech Composites

Unidirectional vs. Woven Carbon Fiber

After creating the individual carbon fibers, manufacturers bundle them into ribbons call tow. Typically tow is comprised of thousands of fibers; 1K (1,000 fibers), 3K, 6K, 12K, 24K, and 50K are common sizes.

Woven fabrics and unidirectional sheets and tapes are all created from tow.

Woven fabrics come many biaxial (fibers running in two directions) and triaxial (three directions) varieties. The 'checkboard' pattern which most people associate with carbon fiber is a 1x1 weave using 3K tow.

Carbon fiber tow

What makes Carbon Fiber so strong?

Carbon fiber is made from the same stuff that comprises diamond; carbon.

What is Prepreg?

Prepreg refers to carbon fiber sheets which have 

Stiffness vs. Strength

Stiffness and strength are terms that are often incorrectly used interchangeably. In fact, with many materials, high stiffness can lead to brittleness and a lack of strength, while many strong materials will be flexible.

Fortunately, carbon fiber can and often does, have both high stiff ness and high strength.