Understanding Fiber-reinforced Plastics

Today, the use of fiber-reinforced plastics in products and applications has dramatically high due to their various properties. They are relatively a new class of non-corrosive, high-strength, lightweight materials. The primary component is plastic which contains fibers such as glass (in fiberglass), carbon (in carbon fiber reinforced polymer), aramid, or basalt. Other fibers like paper, wood, or asbestos are also used but are not common.

Fiber-reinforced plastics or polymers (FRPs) are commonly used in the aerospace, automotive, marine, and construction industries. All these will be further explained in this article.

Today we’ll be going in-depth to see the definition, applications, components, properties, types, forming process, and material requirements of fiber-reinforced plastics. We’ll also get to know their advantages and disadvantages.

Contents

What are fiber-reinforced plastics?

Fiber-reinforced plastics (FRP), also called fiber-reinforced polymers are categorized as composite plastics specifically using fiber materials to mechanically increase the elasticity and strength of the plastic. They consist of a polymer matrix, which is the original plastic (usually tough but weak). The material is blended with reinforcing material to yield a final product with the desired material or mechanical properties. Let’s get to understand this in detail!

Conventionally, a polymer is generally formed by the process of polymerization or addition polymerization. It can be combined with various agents to enhance or increase its material properties, which can then be referred to as plastics. Composite plastics are types of plastics that result from two or more homogeneous materials with different material properties to get a final product with certain desired material and mechanical properties. A good example of composite plastic is fiber-reinforced plastic because fiber materials are used to mechanically enhance the strength and elasticity of plastics. The polymer is usually a vinyl ester, or polyester thermosetting plastic, epoxy, and phenol-formaldehyde resins are also used.

Applications of a fiber-reinforced plastic

Below are the applications of FRP in various fields.

Automotive industry

Fiber-reinforced plastic has become the substitution for metal in the bodies of modern luxury automobiles and truck and trailer body sidings. This is because they are almost of the same strength but different weights, moreover, a high strength-to-weight ratio is a holy grail for the automotive industry. FRPs have higher fracture points than steel and are strong, stiff, and light material which improves fuel consumption while increasing the speed. The material is easily molded to form the desired components. The utilization of this composite plastic is dramatically high in this field.

A type of fiber-reinforced plastic, such as glass FRPs is used for engine components like the intake manifold. This reduces up to 60% of its weight and streamlines the design. Although, glass FRPs are weaker and can be easily bent when compared to carbon FRPs.

Consumer goods

Today in our daily life, it is easier to heft equipment, most especially for sportspeople. This is because carbon and other fiber-reinforced plastic are used to make goods. Almost 6% of FRPs are being used to produce consumer goods. Other items like musical instruments or their components, firearms, camping tents, and camera tripods have also benefited from these materials.

Protective equipment

An extremely high thermal and impact-resistant material is produced when compounds known as aramids are used in FRPs. Exceptional mechanical strength is obtained when used. This is why it is perfect for making bullet-proof and fire-resistant suits, blast-protection vehicles, and structures.

Construction industry

The field of construction has taken about 20% of fiber-reinforced plastic including bridges and roads. The application of FRPs in construction may be used to retrofit slabs, columns, or beams of existing structures. This enhances their load-bearing capacity or repair damages. Fiber-reinforced plastic is extremely cost-effective and useful when it comes to equipping older structures that bear loads far greater than they were designed to face.

FRPs are also used to manufacture highway structures like signboards, guardrails, drainage systems, and bridge decks. Auto skyways, utility poles, and pipelines of gas, water, and sewage also take advantage of the material. FRPs may be perfect for building prefabricated houses, but it’s popularly used for household and business office furniture, household appliances, swimming pools, rain gutters, bathroom equipment, and pipe fittings and hoods.

Power industry

Expectedly, the demand for FRP is expected to grow by over 300% in industry and energy applications. Especially in electronic and electrical components.

Most FRPs are good electrical insulators, tolerate rugged environmental chemicals including corrosive ones, and can resist degradation due to heat. Also, they are relatively non-flammable, have good structural integrity, and can even tolerate ultraviolet radiation. Glass-FRPs are non-magnetic and can also resist sparking, making them useful in power components.

Finally, reinforced plastics are used to construct wind turbine blades and for the storage modules of gas tanks.

Aerospace applications

The applications of FRPs in the aerospace field are increasing because of lower environmental costs and further development. Carbon fibers in FRPs reduce the weight by 25% but ensure equal or greater strength when compared to aluminum sheets. They offer good tensile strength and can tolerate harsh environments and extremely high temperatures. Although, they expand little with heat and possess high stiffness.

Application of FRPs in the aerospace industry is initially expensive, but still, saves more money since every gram of additional weight is grudged due to the effect on fuel consumption, journey length, costs, aerodynamic safety, etc.

With carbon-FRPs complex parts can be easily molded, reducing the number of parts by an astonishing 95%. This makes production simpler, cheaper, and faster compared to other materials like steel or cast aluminum. Modern giant aircraft are made of more than 50% carbon-FRP, and parts like helicopter rotor blades on high-end drones are also increasingly being made of the material.

Marine infrastructure

The fiber-reinforced polymer has become the ideal replacement for wood, on ships, or in marine waterfront environments. This helps to obtain reduced structural weight and enhance corrosion resistance. Other applications include floating causeways and platforms for sea bases and rolling bridges.

Components of composite materials

Below are the components that make up fiber-reinforced plastic.

Fibers:

A chosen fiber usually controls the properties of composite materials. The three major types of fibers used in construction include carbon, glass, and aramid. It is often named by the reinforcing fiber, for instance, CFRP for Carbon FIbre Reinforced Polymer. The most common and important properties that differentiate fiber types are tensile strain and stiffness.

Matrices

The matrix can transfer forces between the fibers and will protect them from detrimental effects. Thermosetting resins are almost exclusively used in this situation. The most common matrices are vinyl ester and epoxy. Well. Epoxy is often favored above vinyl ester but is also more costly. Epoxy matrices have a pot life of around 30 minutes at 20 degrees Celsius but can be changed with different formulations. It has good strength, bond, creep properties, and chemical resistance.

Fig. 2: Fibre Plus Matrix produces FRP

Furthermore, the original plastic material without fiber reinforcement is known as a matrix or binding agent. This matrix is tough and also relatively weak plastic that is reinforced by stronger stiffer reinforcing filaments or fibers. The level of strength and elasticity that is enhanced in a fiber-reinforced plastic depends on the mechanical properties of both matrix and fiber. Their volume is relative to one another, and the fiber length and orientation within the matrix are also considered. Reinforcement of the matrix occurs by definition when the FRP material exhibits increased strength or elasticity relative to the strength and elasticity of the matrix alone.

Common properties of fiber-reinforced plastics

Just as earlier mentioned, the characteristics of fiber-reinforced plastics depend upon factors such as the mechanical properties of the matrix and the fiber. The volume of both and their length, and orientation of the fibers in the matrix.

The reason why FRPs are widely considered is because of their low weight but are incredibly strong, and have good fatigue. Also, its impacts and compression properties are a unique reason. This is why motor industries were able to replace metals with lighter-weight materials to not only make the cars stronger but also faster and fuel-efficient.

Fiber-reinforced plastics also demonstrate distinctive electrical properties and high-grade environmental resistance, along with good thermal insulation, structural integrity, fire hardiness, UV radiation stability, and resistance to chemicals and corrosives. Well, all these were mentioned above.

Material requirements or common fibers materials

Below are the fibers used to get a specific type of reinforced polymer.

Glass:

glass which acts as a good insulator forms fiberglass or glass-reinforced plastics when combined with the matrix. Plastics reinforced with glass are beneficial to the power industry as they have no magnetic field and are resistant to electrical sparks. They are incorporated into engine intake manifolds where they offer a 60% decrease in weight over cast-aluminum manifolds. Finally, improved surface quality and aerodynamics are obtained for these materials.

The glass FRP has also been used in gas and clutch pedals in cars as they can be molded into a single unit. The fibers are oriented in a way that they support specific stresses, increasing durability and safety. However, these reinforced materials are not strong, rigid, or brittle as carbon fiber-reinforced materials. It can be expensive to produce.

Carbon

Carbon fiber materials exhibit high tensile strength, chemical resistance, stiffness, and temperature tolerance. Carbon atoms create crystals that lie along the axis of the fiber, which helps to strengthen the materials by increasing the strength-to-volume ratio. Just as earlier explained, carbon fiber-reinforced plastics are used in sporting goods, gliders, fishing rods, etc.

Carbon FRPs have been incorporated into the rudders of an Airbus A310, which has helped to decrease its number of components by 95%. The simple molded parts have reduced production cost and operational costs. They are now 25% lighter than the ones produced with sheet aluminum, which makes them more fuel-efficient.

Aramids

Aramids are classified as synthetic polyamides formed from aromatic monomers (ring-shaped molecules). This demonstrates robust heat resistance, which is why they are used for bullet-proof and fire-resisting clothing.

Aramids are generally prepared by the reaction between an amine group and a carboxylic acid halide group (aramid). This exists when an aromatic polyamide is spun from a liquid concentration of sulphuric acid into a crystallized fiber. Fibers are then spun into larger threads to weave into large ropes or woven fabrics. Aramid fibers can be manufactured at varying grades based on strength and rigidity, so that the material can meet specific design requirements, such as cutting the tough material during manufacture.

Types of fiber-reinforced polymer (FRP)

Below are the major types of fiber-reinforced polymers.

Glass fiber-reinforced polymer (GFRP)

Glass fibers are made from silica sand, limestone, folic acid, and some other minor ingredients mixed. This mixture is heated until it melts at about 1260⁰C. The molten glass is allowed to flow through fine holes in a platinum plate. The glass strands are cooled, gathered, and wound. The fibers can then be drawn to increase their dimensional strength. It is then woven into various forms for use in composites.

Glass-produced fibers are considered the predominant reinforcement for polymer matrix composites, based on an aluminum lime borosilicate composition. This is because of their high electrical insulating properties, high mechanical properties, and low susceptibility.

Generally, glass is a good impact-resistant fiber but weighs more than carbon or aramid. Glass fibers have excellent characteristics equal to or better than steel in certain forms.

Glass Fibre Reinforced Polymer Bars

Aramid fiber-reinforced polymer (AFRP)

Aramid is also known as aromatic polyamide. A well-known trademark of aramid fibers is called Kevlar but there do exist other products like Twaron, Technora, and SVM. The modulus of the fibers ranges from 70-200 GPA with an ultimate elongation of 1.5-5% depending on the quality. Aramid has high fracture energy, which is why it can be used for helmets and bullet-proof garments.

AFRP is sensitive to elevated temperatures, moisture, and UV radiation and is not common with civil engineering applications. Finally, aramid fibers have problems with relaxation and stress corrosion.

Properties of Different Types of FRP Compared with Steel

The forming process of fiber-reinforced plastic

Most fiber-reinforced plastic parts are made with a mold or tool. The mold used can be concave female molds, or male molds, or the part can be completely enclosed with a top or bottom mold. But a rigid structure is usually used to establish the shape of FRP components. parts can either be laid upon flat surfaces which are known as “caul plates” or on a cylindrical structure referred to as “mandrel”.

The molding processes of fiber-reinforced plastics are accomplished by placing the fiber preform on or in the mold. This fiber preform can be dry fiber or fiber that already contains a measured amount of resin known as “prepreg”. The dry fibers are wetted with resin either by hand or the resin is injected into a closed mold. At this point, the part is cured, leaving the matrix and fibers exactly as the mold shape. Another way the resin is cured and how to improve the quality of the final part is by using heat and/or pressure.

Watch the videos below to learn more about the forming process of fiber-reinforced plastics:

https://www.youtube.com/watch?v=WgwDI1oOQNc

Below is the various method of forming fiber-reinforced plastic.

Bladder molding:

This forming process is when individual sheets of prepreg material are laid up and placed in a female-style mold along with a balloon-like bladder. The mold will then be closed and placed in a heated press. Finally, the bladder is pressurized forcing the layer of material against the mold walls.

Compression molding:

A compression-molded part is known as fiber-reinforced plastic. So, when a raw material like plastic block, rubber block, plastic sheet, or granules, it is called so. The plastic preform used in compression molding does not contain reinforcing fibers. In this molding, a preform or charge of SMC or BMC is placed into the mold cavity. The mold is then closed and the material is formed and cured inside using heat and pressure. compression molding is known for its excellent detailing for geometric shapes ranging from pattern and relief detailing to complex curves and creative forms to precision engineering.

Autoclave and vacuum bag:

Each sheet of prepreg material is laid-up and placed in an open mold, which is then covered with release film, bleeder or breather material, and a vacuum bag. A vacuum is pulled on the part and the mold is placed into an autoclave, also known as a heat pressure vessel. The part is cured with a continuous vacuum to extract entrapped gasses from the laminate. This process is common in the aerospace industry because it offers precise control over molding due to a long, slow cure cycle. The time ranges from one to several hours. This precise control help to create the exact laminate geometric forms needed to ensure strength and safety in the aerospace industry. However, it is slow and labor-intensive, that is, cost often confines it to the aerospace industry.

Mandrel wrapping:

In this forming process of fiber-reinforced plastic, sheets of prepreg material are wrapped around a steel or aluminum mandrel. This prepreg material is compacted by polypropylene cello tape or nylon. The parts are batch cured by vacuum bagging and hanging in an oven. After performing the cure, the cello tape and mandrel are removed leaving a hollow carbon tape. This helps to create strong and robust hollow carbon tubes.

Wet layup:

This forming process combines fiber reinforcement and the matrix as they are placed on the forming tool. Reinforcing fiber layers are placed in an open mold, which is then saturated with a wet resin by pouring it over the fabric and working into the fabric. The mold will be left for some time so that the resin will cure, usually at room temperature. Although heat can sometimes be used to make sure it is properly cured. A vacuum bag is used to compress a wet layup. Glass fibers are the most common for this process, which result is known as fiberglass. It is used to make products like skis, canoes, surfboards, etc.

Resin transfer molding:

This forming process of fiber-reinforced plastic is also called resin infusion. Fabrics are laid into a mold into which wet resin is injected. Resin is typically pressurized and forced into a cavity that is under vacuum in resin transfer molding. The resin is entirely pulled into the cavity under a vacuum in vacuum-assisted resin transfer molding. This process ensures precise tolerance and detailed shaping. Although it sometimes fails to fully saturate the fabric leading to spots in the final shape.

Filament winding:

In this process, there are machines that pull fiber bundles through a wet bath of resin and wound over a rotating steel mandrel in specific orientations. Parts are cured either at room temperature or elevated temperatures. The mandrel is extracted, leaving a final geometric shape, although it is left in some situations.

Pultrusion:

Fibre bundles and slit fabrics are pulled through a wet bath of resin which then formed the rough part shape. Saturated material is extruded from a heated closed die, which is cured while being continuously pulled through the die. Most end products of pultrusion are structural shapes, i.e. beam, angle, channel, and flat sheet. The materials can be used to create all sorts of fiberglass structures like ladders, handrail systems tanks, platforms, pipes, and pump supports.

Chopper gun:

Continuous strands of fiberglass are pushed through a hand-held gun that both chops the strands and joins them with a catalyzed resin such as polyester. The impregnated chopped glass is then shot onto the mold surface in the appropriate thickness and design the human operator thinks is right. The chopper gun process is ideal for large production runs at economical cost, but it produces geometric shapes with less strength than other molding processes and has poor dimensional tolerance.

Advantages and disadvantages of fiber-reinforced plastic

Advantages:

Below are the advantages of fiber-reinforced plastics in their various applications.

FRPs have high strength
They have a high modulus of elasticity
They are lighter in weight
High resistance to fatigue failure is another excellent benefit.
They have good corrosion resistance.
Stiffness is another great benefit of FRPs as it is up to 3.3 times rigid as timber and will not permanently deform under a working load.
Resistance to rot, and insects.
The final product of fiber-reinforced plastic can be appealing, so it might not require paints, stains, and coatings.
Flexibility in their fabrication and designing process
FRPs are good insulators with low thermal conductivity.
Fiberglass types of FRP are resilient, that is, the material has a hard finish.
Maintenance and installation of FRPs are lower, even though stainless steel has a lower initial material cost than fiber-reinforced plastic.

Disadvantages:

Despite the great benefits of fiber-reinforced plastic, some limitations still occur. below are the disadvantages of FRPs.

Their strength in a direction perpendicular to the fibers is extremely low (up to 5%) compared with the strength along the length of the fibers.
Material Design can be complex
Testing and manufacturing of FRP components are highly specialized.

Conclusion

In this article, you’ve learned about fiber-reinforced plastics, their definition, applications, composite components, and material requirement. We also discussed the various types, forming processes, and advantages and disadvantages of fiber-reinforced plastics.

I hope you enjoyed the reading, if so, kindly comment on your fav section of this article. And please don’t forget to share this article with other technical students, it might be of help to them. Thanks!

Understanding fiber reinforced plastic