Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 510 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment gives the fiber high strength-to-volume ratio (making it strong for its size). Several thousand carbon fibers are bundled together to form a tow, which may be used by itself or woven into a fabric.
Carbon fiber is a high-tensile fiber or whisker made by heating rayon or polyacrylonitrile fibers or petroleum residues to appropriate temperatures. Fibers may be 7 to 8 microns in diameter and are more that 90% carbonized.
These fibers are the stiffest and strongest reinforcing fibers for polymer composites, the most used after glass fibers. Made of pure carbon in form of graphite, they have low density and a negative coefficient of longitudinal thermal expansion.
Carbon fibers are very expensive and can give galvanic corrosion in contact with metals. They are generally used together with epoxy, where high strength and stiffness are required, i.e. race cars, automotive and space applications, sport equipment.
Depending on the orientation of the fiber, the carbon fiber composite can be stronger in a certain direction or equally strong in all directions. A small piece can withstand an impact of many tons and still deform minimally. The complex interwoven nature of the fiber makes it very difficult to break.
Characteristics/Properties of Carbon Fibers
1. Physical strength, specific toughness, light weight.
2. Good vibration damping, strength, and toughness.
3. High dimensional stability, low coefficient of thermal expansion, and low abrasion.
4. Electrical conductivity.
5. Biological inertness and x-ray permeability.
6. Fatigue resistance, self-lubrication, high damping.
7. Electromagnetic properties.
8. Chemical inertness, high corrosion resistance.
Classification of Carbon Fiber:
Based on modulus, strength, and final heat treatment temperature, carbon fibers can be classified into the following categories: