What is Carbon Fibre
Carbon Fibre is long thin strands mostly made from carbon atoms which are bonded together in microscopic crystals.
The crystal is aligned which makes them incredibly strong. They are then twisted together, very similar to the cotton-producing process, into yarn. The yarn is then woven together to create Carbon Fibre Cloth. There are different types of weave for carbon fibres:
- Plain: Also known as bidirectional standard over/under Very easy to handle, because of a tight weave.
- Twill: Diagonal pattern from an over-over and under-under It is the most recognisable carbon fibre pattern and offers a looser form than a plain design, making it better for more complex shapes.
- Satin: Satin has a brick like resemblance which comes from a number over-overs (typical four or eight) to one under. The pattern is not the easiest to work with and is best suited to complex curves.
- Unidirectional: As the name suggests, all the yarn is one directional. There is no weave, and it is often held together with a thread, though this does not alter the structure of the carbon fibre. It is most suited to moulds that have a force acting only on one axis
How is Carbon Fibre Made?
Each manufacturer of carbon fibre has their way of manufacturing the material to give it its strength or aesthetic selling features. However, as a rule, all carbon fibre comes from organic polymers which are strings of molecules held together by carbon atoms.
The PAN (polyacrylonitrile) manufacturing process accounts for around 90% of all carbon fibre manufacturing and is a five-step process:
- Polyacrylonitrile is mixed with other items and spun to create fibres which are stretched and cleaned.
- Chemicals are then added to stabilise
- Heat gets added, high temperatures help form tightly bonded carbon crystals.
- Fibres are oxidised to improve bonding properties.
- Finally, strands are coated and wound into different sized threads. Before a carbon fibre becomes a composite material a polymer gets added and heat, pressure or a vacuum bind the thread with the polymer to create a composite material.
As with any manufacturing process, the materials used will create specific qualities and effects in the carbon fibre, thus allowing for grading and application differences.
What are the Benefits of Carbon Fibre?
Carbon fibre is well known for its low weight and high strength, making it the ideal advanced composite material in the Marine, Automobile and Aerospace industries. Key benefits include:
- Excellent strength to weight ratio
- High heat resistance
- High chemical/corrosion resistance (when used with the correct resin)
- Extremely flexible, making it suitable for a range of applications
- Excellent fatigue properties
- Works with a variety of different materials
- Electrical and thermal conductivity
- Possesses a low coefficient of thermal expansion
What are the Downsides of Carbon FIbre?
Despite having a wide range of advantages, carbon fibre is still a relatively new composite material which does come with some disadvantages:
- Expensive compared to other composite materials
- More labour intensive to manufacture
- Not currently recyclable, often carbon fibre is used to replace steel or aluminium, both of which are recyclable materials
- Will break/shatter when pushed beyond its capabilities
- If damaged, it must be replaced rather than repaired like metal structures
What is Kevlar/Aramid Fabrics?
Kevlar is a fabric that is exclusively made by Du Point. It is created using aramid polymers where the molecules get arranged in parallel lines; the fibres are then knitted tightly together.
How is Kevlar Made?
There are two steps to making Kevlar.
- The first step is a chemical process that involves producing the basic plastic from which Kevlar gets made into long string fibres.
- The second part of the process often is referred to as a condensation process. During this process the molecular chains line up parallel to each other and are cross-linked with hydrogen bonds, giving Kevlar its high-tensile strength.
What are the Benefits of Kevlar?
- Strong, while still lighter than steel
- Good heat resistance – starts to decompose around 450 ° C
- Good chemical resistance
- Unaffected by moisture
What are the Downsides of Kevlar?
- Poor compressive strength – resistant to squashing and squeezing
- More sensitive to environmental factors than other materials
- Requires specially made scissors to sever dry fabric
- Once laminated it can only be pierced with specially made drill bits
Which is the Best One for Me?
Carbon is best suited for areas that require a higher stiffness and strength. While carbon fibre offers the best strength and rigidity to weight in the industry; it is also generally the most expensive of reinforcements.
Carbon fibre is also much more straightforward to cut, sand and machine in comparison to Kevlar, which requires specially made drill bits once laminated.
That said, Kevlar offers a better abrasive strength than carbon fibre, which is why it commonly associated with bulletproof vests. Kevlar is also better in extreme temperatures than carbon fibre, which some indicate make it better suited in the marine industry.