Continuous multi-filament TOW.
The most common form of carbon fiber is the high strength, high stiffness form commonly used in composites. These are made by a complicated process from textile pre-cursor yarns made from either polyacrylonitrile (PAN) or pitch that results in a predominantly graphitic stucture highly oriented in the direction of the fiber axis. This high orientation gives them their remarkable properties which include a small negative coefficient of thermal expansion in the axial direction as well as remarkably high specific strength and stiffness. These fibers are available from stock in a range of stiffnesses and, to a lesser extent, strengths, together with several types of fabric all made from carbon fiber of the most common property level i.e. 230GPa (Type XAS or 300). In addition, there are available from stock one fiber and one fabric of entirely different forms of carbon. The fiber is a sewing thread construction made from carbon yarn of much lower tensile properties in order to give a really flexible thread and the fabric is of activated charcoal (not available as yarn as it is made directly from a pre-cursor textile fabric.