A Fibre Reinforced Polymer composite is defined as a polymer that is reinforced with fibre. The primary function of fibre reinforcement is to carry the load along the length of the fibre and to provide strength and stiffness in one direction.
FRP represents a class of materials that fall into a category referred to as composite materials.
Composite materials consist of two or more materials that retain their respective chemical and physical characteristics when combined together.
FRP composites are different from traditional construction materials like steel or aluminium.
FRP composites are anisotropic (properties appear in the direction of applied load) whereas steel or aluminium is isotropic (uniform properties in all directions, independent of applied load).
Therefore FRP composites properties are directional, meaning that the best mechanical properties are in the direction of the fibre placement.
Fibre-reinforced plastic (FRP), also known as fibre-reinforced plastic, is a composite material made of a fibre-reinforced polymer matrix.
Glass, carbon, or aramid are usually the fibres, although other fibres have sometimes been used, such as paper or wood or asbestos.
The polymer is generally a thermosetting plastic of epoxy, vinylester or polyester, and phenol formaldehyde resins are still in use. In the aerospace, automotive, marine, and construction industries, FRPs are commonly used.
Composite Components of Fibre Reinforced Polymer
The composite’s properties are mainly influenced by the choice of fibres. In civil engineering three types of fibres dominate.
These are carbon, glass, and aramid fibres and the composite is often named by the reinforcing fibre, e.g.CFRP for Carbon Fibre Reinforced Polymer.
They have different properties. For strengthening purposes carbon fibres are the most suitable.
All fibres have generally higher stress capacity than the ordinary steel and are linear elastic until failure.
The most important properties that differ between the fibre types are stiffness and tensile strain.
The matrix should transfer forces between the fibres and protect the fibres from the environment. In civil engineering, thermosetting resins (thermosets) are almost exclusively used. Of the thermo sets vinyl ester and epoxy are the most common matrices.
Epoxy is mostly favoured above vinyl ester but is also more costly. Epoxy has a pot life around 30 minutes at 20 degree Celsius but can be changed with different formulations. The curing goes faster with increased temperature. Material properties for polyester and epoxy are shown in table 2. Epoxies have good strength, bond, creep properties and chemical resistance.
TYPES OF FIBRE REINFORCED POLYMERS
The different types of fibre reinforced polymer are glass fibre, carbon, aramid, ultra-high molecular weight polyethene, polypropylene, polyester and nylon. The change in properties of these fibres is due to the raw materials and the temperature at which the fibre is formed.
1. Glass fiber reinforced polymer
Glass fibres are basically made by mixing silica sand, limestone, folic acid and other minor ingredients. The mix is heated until it melts at about 1260°C.
The molten glass is then allowed to flow through fine holes in a platinum plate. The glass strands are cooled, gathered and wound.
The fibres are drawn to increase the directional strength. The fibres are then woven into various forms for use in composites.
Based on an aluminium lime borosilicate composition glass produced fibres are considered the predominant reinforcement for polymer matrix composites due to their high electrical insulating properties, low susceptibility to moisture and high mechanical properties. Glass is generally a good impact resistant fibre but weighs more than carbon or aramid. Glass fibres have excellent characteristics equal to or better than steel in certain forms.
2. Carbon Fibre Reinforced Polymer
Carbon fibres have a high modulus of elasticity, 200-800 GPa. The ultimate elongation is 0.3-2.5 % where the lower elongation corresponds to the higher stiffness and vice versa. Carbon fibres do not absorb water and are resistant to many chemical solutions.
They withstand fatigue excellently, do not stress corrode and do not show any creep or relaxation, having less relaxation compared to low relaxation high tensile prestressing steel strands.
Carbon fibre is electrically conductive and, therefore might give galvanic corrosion in direct contact with steel.
3. Aramid Fibre Reinforced Polymer
Aramid is the short form for aromatic polyamide. A well-known trademark of aramid fibres is Kevlar but there exists other brands too,e.g Twaron, Technora and SVM. The moduli of the fibres are 70-200 GPa with an ultimate elongation of 1.5-5% depending on the quality.
Aramid has high fracture energy and is therefore used for helmets and bullet-proof garments. Aramid fibres are sensitive to elevated temperatures, moisture and ultraviolet radiation and therefore not widely used in civil engineering applications.
Further aramid fibres do have problems with relaxation and stress corrosion.
fibre reinforced plastic properties
Fibre reinforced plastics (FRPs) are composite materials made up of two or more different materials that have been combined to create a new material with different properties than the individual components. The two main components of FRP are the fibres and the matrix.
The fibres are the reinforcing component of FRP. They are typically made of glass, carbon, or aramid, and they are very strong and stiff. The matrix is the surrounding material that holds the fibres in place. It is typically made of a polymer, such as epoxy or polyester, and it provides the FRP with its toughness and durability.
FRPs have a wide range of properties, including:
- High strength to weight ratio: FRPs are much stronger than their weight would suggest. This makes them ideal for applications where weight is a critical factor, such as aerospace and automotive.
- High stiffness: FRPs are very stiff, which makes them resistant to deformation. This makes them ideal for applications where strength and rigidity are important, such as structural components.
- Good fatigue resistance: FRPs are very resistant to fatigue, which means they can withstand repeated loading and unloading without failing. This makes them ideal for applications where there are a lot of vibrations, such as in the marine industry.
- Good corrosion resistance: FRPs are very resistant to corrosion, which makes them ideal for applications where they will be exposed to harsh environments, such as the marine environment or the chemical industry.
- Low thermal conductivity: FRPs have a low thermal conductivity, which means they are good insulators. This makes them ideal for applications where heat insulation is important, such as in the construction industry.
FRPs are a versatile material with a wide range of properties. They are used in a variety of industries, including aerospace, automotive, construction, marine, and electrical.
Here are some specific examples of the properties of FRPs:
- Glass fibre reinforced plastics (GFRPs) have a tensile strength of up to 3000 MPa and a flexural strength of up to 2000 MPa.
- Carbon fibre reinforced plastics (CFRPs) have a tensile strength of up to 5000 MPa and a flexural strength of up to 3000 MPa.
- Aramid fibre reinforced plastics (AFRPs) have a tensile strength of up to 4000 MPa and a flexural strength of up to 2500 MPa.
The properties of FRPs can be tailored to meet the specific requirements of an application. For example, the type of fibre used, the length of the fibres, and the orientation of the fibres can all be adjusted to achieve the desired properties.
FRPs are a valuable material with a wide range of applications. They are strong, lightweight, and corrosion resistant, making them ideal for a variety of industries.
ADVANTAGES OF FIBRE REINFORCED POLYMERS
The advantages of FRP are
- FRP can provide a maximum material stiffness to density ratio of 3.5 to 5 times that of aluminium or steel.
- It has high fatigue endurance limits
- It can absorb impact energies
- The material properties can be strengthened where required
- The corrosion potential is reduced
- Joints and fasteners are eliminated or simplified.