Carbon fibers have diameters ranging from about 5 to 10μm and are composed primarily of carbon atoms. They are obtained by oxidation and carbonization in furnaces of polyacrylonitrile or PAN fibers. Their structure consists in a superposition of long and flat microcrystals aligned parallel to the fiber axis. The main properties of carbon fibers are:
- high tensile and compressive strengths
- high modulus
- low density
- high chemical resistance
- high temperature tolerance
- electrically conductive
The variation of process parameters (temperatures, times etc.) can provides fibers with different characteristics: high or intermediate modulus, high tenacity etc.
Carbon fiber and other materials properties
| Material | Tensile strengh (MPa) | Tensile modulus (GPa) | Elongation (%) | Density (g/cm3) | Strengh-to-weight ratio (MPa/g/cm3) |
|---|---|---|---|---|---|
| Carbon fiber (1) | 5407 | 294 | 1.75 | 1.79 | 3026 |
| Kevlar 49 (5) | 3650 | 124 | 2.5 | 1.44 | 2535 |
| S-Glass (5) | 4600 | 88 | 5.5 | 2.49 | 1847 |
| Boron (5) | 3620 | 400 | 1 | 2.57 | 1409 |
| Titanium alloy Ti-6Al-4V (type 5) (2) | 620 | 113.8 | 14 | 4.43 | 140 |
| High Carbon Steel (4) | 1010 | 198 | 14.6 | 7.49 | 135 |
| Aluminum alloy 6061-T6 (3) | 310 | 68.9 | 17 | 2.7 | 115 |
(1) average value calculated from HexTowTM carbon fibers data supplied by HexcelTM.
(2) titanium Ti-6Al-4V (Grade 5) annealed, data from matweb.com
(3) aluminum 6061-T6 data from matweb.com
(4) high carbon steel data average values from matweb.com
(5) data from engineeringtoolbox.com
A carbon fiber yarn, or tow, comprises several thousand fibers. For example, a 12K tow is a made of 12,000 fibers. Carbon fibers are supplied in spools of 1K, 3K, 6K, 12K, 24K or 48K tows. Carbon fiber fabrics are woven from carbon tows. They are finally used with a matrix (epoxy or polyester resin, ceramics) to obtain a composite parts.