Prepreg Carbon Fiber

Woven vs. Unidirectional Carbon Fiber

Carbon fiber materials can be categorized as either woven or unidirectional, depending on how they are formed. Unidirectional carbon fiber is non-woven, so it does not have any weave pattern. Instead, its fibers lie parallel to one another with no gaps. This method of construction maximizes longitudinal tensile potential, so it is ideal for applications requiring strength in a single direction. However, many applications subject composite materials to multidirectional tensile forces. Woven carbon fibers are more appropriate for these applications. Woven fabrics also tend to be more workable and machinable than unidirectional fiber.

Common Weave Patterns 

Woven carbon fiber materials can be further classified based on their weave, or the pattern used to join fibers into a fabric. These differences are not purely aesthetic—different weaves look very different from one another, but they also have distinct performance characteristics. Accordingly, some weaves are more appropriate for certain applications than others. 

First, the fibers are bundled into groups called tows, 3K and 12K are standard industry fiber bundles which are 3,000 and 12,000 fibers densely packed together. The way these tows are combined determines the fabric’s strength, stability, and formability.

• Plain Weave. The simplest carbon fiber weave is known as a plain weave. The plain weave is formed by crossing tows in a one-over, one-under pattern, creating the checkerboard seen on many woven fabrics. These materials are strong and highly stable, but they are not very pliable. Plain woven carbon fiber is best for components that are flat or only slightly contoured.
• Twill Weave. Like the plain weave, the twill weave comes from passing tows in an even over/under pattern. However, rather than passing over a single tow, each strand passes over multiple tows, then under the same number of tows. This is typically done in a two-over, two-under pattern, but 4 x 4 twills are also common. In either case, the resulting pattern appears to form rows of rectangles proceeding diagonally up the fabric. Twill weaves are more formable than plain weaves, so they can be used with more complex shapes. However, this means that they are not as stiff and stable as plain weaves.

Spread Tow Weaves

“Spread tow” does not describe a specific weave pattern. Instead, it refers to fabrics woven with wider, thinner tows than usual, which can be combined into the weave patterns described above. These “spread tows” create smoother, lighter weight fabrics because they spread stress more evenly than standard tows. Any woven fabric has a crimp angle, which is the angle formed at the intersection of fibers. Stress can become concentrated at these intersections, changing the strength of the fabric. Spreading the tows creates shallower crimps that accumulate less stress. 

Prepreg Carbon Fiber Applications

Prepreg materials are easy to work with while offering highly favorable mechanical properties. They can also be safer and more friendly than other resin methods. Carbon fiber prepregs, in particular, are known for their strength, stiffness, and resistance to both chemicals and extreme temperatures. These properties, coupled with carbon fiber’s extremely light weight, benefit both military and industry applications, including:

• Aircraft interiors
• Aerospace components
• Shielding and reinforcements
• Cargo liners and airplane flooring
• High-end automotive parts and components
• Electrical vehicle and drone components
• High-temperature components
• Prosthetics and medical devices

The team at APCM can help you determine which prepreg is the best match for your application.