Carbon Fibre Reinforced Plastics
The Composite’s properties are mainly influenced by the choice of fibers. Three types of fibres are Glass fibre, Carbon fibre, Aramid fibre. All fibres have generally higher stress capacity than ordinary steel and are linear elastic until failure. The most important properties that differ between the fibre types are stiffness and tensile strain.
Carbon fiber reinforced polymer (CFRP) is a type of composite materials consist of carbon fiber and polymer. The carbon fiber provides the strength and stiffness while the polymer acts as cohesive matrix to protect and held the fibers together. Carbon fibre reinforced plastics are manufactured as a strips, bars, and sheets using different production technique like filament winding, pultrusion, and hand lay-up processes.
Carbon Fibre Reinforced Plastics Properties:
Composite materials, reinforced with carbon fibre, are different than other FRP composites using traditional materials such as fibreglass or aramid fibre.
- High Modulus of Elasticity 200 – 800 GPa.
- Tensile Strength 2500 – 6000 MPa.
- Density 1750 – 1950 Kg / m3.
- Ultimate Elongation 0.3 – 2.5 %.
- Carbon fibre reinforced plastics do not absorb water.
- Carbon fibre reinforced plastics are resistant to many chemical solutions.
- Carbon fibre reinforced plastics withstand fatigue excellently.
- Carbon fibre reinforces plastics do not show any creep or relaxation.
- Carbon fibre reinforced plastics is electrically conductive.
- Light weight than other FRP composites
- Increased strength than other FRP composites
What is Composites?
When the fibre and the matrix are combined into a new material it becomes a composite. The fibres may be placed in one direction in the composites and then the composite is unidirectional. However fibres may also be woven or bonded in many directions and the composite becomes bi or multi directional.
Carbon fibers are the product of a high-tech manufacturing process. It starts with a starting product such as polyacrylonitrile (PAN). Polyacrylonitrile is a solid in the form of a white powder. It is hard and stiff as well as resistant to chemicals and solvents. In a first process step, thin threads are produced from it, which are then wound onto a spool – the so-called PAN “precursor” has been created.
In the next step, these threads are placed in the oven. First, they are oxidized at 200 to 300 degrees Celsius and then carbonized at 1200 to 1800 degrees Celsius. What remains are threads with a very high carbon content and high strength. After surface treatment and application of a sizing, the carbon fiber is wound up and is ready for use.
- Hand lay up method
- Pultrusion method
- Filament winding
Spinning, Stabilizing, Carbonizing, Surface Treatment and Sizing
The manufacturing process for carbon fiber is partly chemical and partly mechanical.
- Spinning: The PAN is spun using one of a few spinning processes. This step is important because it forms the internal atomic structure of the fiber. The fibers are then washed and stretched to the required diameter. The stretching also helps align the molecules to aid in the formation of the carbon crystals created by carbonization.
- Stabilizing: In this step the fibers are treated with chemicals to change their linear bonding to a thermally stable ladder bonding structure. The filaments are then heated in air so they pick up oxygen molecules and change their atomic bonding pattern.
- Carbonizing: The fibers are then exposed to very high heat without oxygen present so the fiber cannot burn. The atoms in the fiber vibrate violently expelling most of the non-carbon atoms in the precursor.
- Surface Treatment: After carbonizing, the surface of the fibers does not bond well with the materials used in making composite materials. In this step, the surface of the fibers are slightly oxidized by immersion in various gases or liquids.
- Sizing: In this process, the fibers are coated to protect them from damage during winding or weaving.
A few products made from carbon fibers are fishing rods, bicycles, golf equipment, tennis rackets, parts for aircraft’s, bridges, and automobiles.
Manufacturing Methods for CFRP
- Continuous reinforcement process
- Filament winding
- Hand lay-up processes
- Moulding processes
- Matched-die moulding
- Autoclave moulding
- Vacuum bagging
- Resin injection processes
- Resin transfer moulding
- Reaction injection moulding
Carbon Fibre Reinforced Polymers (CFRP):
CFRP is sometimes referred to as Carbon Fibre Reinforced Plastics is similar to fibre glass. Carbon fibre reinforced plastics is woven into a textile material and resin such as epoxy resin is applied and allowed to cure. The resulting material that is very strong as it has the best strength to weight ratio of all construction materials. It is an improvement on glass fibre reinforced plastic, although much more expensive.
Carbon Composite (CFRP) Friction Bearings:
Friction bearings commonly use lubricating oil to separate the moving component from the mated non-moving bearing surface. Friction bearing surfaces commonly consist of a material that is softer than the supported component.
These friction bearings provide excellent dry running characteristics and can be used in operation after lubrication system failure making them an ideal solution for use in pumps and construction machinery as well as in mechanical engineering and shipbuilding or in offshore and onshore facilities to reduce maintenance and increase reliability. It can withstand up to 260 degree Celsius.
Real Life Applications of Reinforced Plastics (CFRP)
1. CFRP Strips
There are many techniques that use CFRP strips, laminates for strengthening concrete structures such as Externally bonded CFRP sheets and Near Surface Mounted FRP. The performance of the strengthening methods depends on the strength of the adhesive used to bond Carbon Fibre Reinforced Plastics to the concrete surface and the degree of stress at the interface of the concrete and Carbon Fibre Reinforced Plastics.
Carbon Fibre Reinforced Plastics is used to strengthen steel road bridges more easily and cheaply. The Carbon Fibre Reinforced Plastics strips are only 20% of the weight of the strips of similar products made from high-strength steel but are at least four times as strong. Their high-strength-to- weight ratio makes the CFRP strips easily to handle and reduces installation costs. Strips of Carbon Fibre Reinforced Plastics measuring just 8 mm in thickness have been used to strengthen a road bridge in Rochdale, UK.
2. CFRP Wraps
CFRP wrapping is used for rehabilitation of masonry columns. Carbon Fibre Reinforced Plastics wraps are used for corrosion control and rehabilitation of reinforced concrete columns. They are also used for construction of earthquake resistant structures.
The addition of CFRP sheets greatly increases the ultimate flexural moment capacity of the retrofitted shear wall. However, in order for the FRP sheet to carry the high axial loads resulting from the bending moment imposed on the shear wall, the Carbon Fibre Reinforced Plastics sheets must be adequately anchored at the base of the wall.
3. CFRP Laminates
Low Thermal Expansion CFRP Laminates are used for strengthening of structural members such as beams in buildings and girders in bridges. Carbon Fibre Reinforced Plastics is used to strengthen steel road bridges more quickly, cheaply and easily.
4. CFRP Bars
CFRP bars have been in the construction of new buildings and strengthening reinforced concrete structures using Near Surface mounted Carbon Fibre Reinforced Plastics Reinforcement technique.