Commercially available fibers–CFCCARBON LTD

Carbon fibers are available from a variety of suppliers in a number of yarns and tows with different module, strengths, cross-sectional areas and shapes, twists and number of fiber ends. They may be purchased in a multitude of different forms including continuous tows, chopped and milled, woven fabrics and three-dimensional performs. The diversity and tailorability of the properties of carbon fibers are one of their advantages but, accordingly, are also a problem in that a complete evaluation is difficult and expensive to obtain. It is possible, however, to make a number of generalizations:

1. The fibers produced from PAN and mesophase pitch have significantly different combinations of properties and hence, applications. At present they cannot be considered interchangeable.
2. There are generally four classes of carbon fibers subdivided by module: low, intermediate, high and ultra high. Subdivision into these categories is not, unfortunately, as straightforward as , for example, metal alloys. Although the fibers made by different manufacturers may be similar they are not identical. Subtle differences in choice of precursor and processing conditions may have quite significant effects on the fiber properties and on its behaviour when combined into a composite. Constant improvements by the suppliers to their products have resulted in a degree of overlap between the categories.
3. The fiber selections that make up a particular manufacturer’s grade, but have different numbers of fibers within the tows, are usually, but not always, based on the same precursor. While the fibers within each grade maybe considered to possess the same properties, the fiber count or degree of twist, etc. may affect subsequent composite properties.
4. It is not possible to list all of the properties of the different suppliers’ products;
5. The range of carbon fiber grades in present use is between 5 and 11um in diameter. The trend is towards smaller and smaller fiber diameters in order to attain improved tensile strength and processing speeds. The compressive and transverse properties of composites employing smaller diameter fiver reinforcement do not increase in proportion with tensile properties. As a result failure in compression may result at lower then predicted loads as a result of buckling. cfccarbon.com
6. Secondary load-bearing structures generally require at least 1.5% strain to failure and primary structures 2% or better. As a result, IM PAN-based grades are generally preferred for such tasks.
7. The major advantage of mesophase pitch-based fibers is that they can be made into ultra high modulus, and their use is generally limited to space structures because of their excessive cost.
8. Great care must be taken when selecting a reinforcing fiber for a carbon-carbon composite to avoid a situation arising in which a component is required to operate at a temperature higher than the temperature at which it was produced, when a corresponding change in properties may result. For this reason a lot of carbon-carbon materials are based on heat-treated fabrics, to ensure that no shrinkage occurs throughout the process.