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Abdel Rahman. No one can say with any certainty what the lifespan of composites are. The reason: the first composites put to work more than 50 years ago are still going strong. For instance, the American classic, the Chevy Corvette, was built with fibre-reinforced plastic back in Then, cars were produced.
Two-thirds of them are still around today. Construction is another industry that makes great use of composites. Entire homes can be framed using composites instead of traditional wood framing. Composites are especially popular with U. Fibre-cement siding mimics the look of wood without the hassle of maintenance. These are just a few areas of a home that can take advantage of what composites have to offer. The aerospace industry is a big fan of composites because they require less maintenance.
Their Dreamliner is the first plane with an airframe constructed mostly of composite materials. While the FAA grounded all s for a month back in , this was due to problems with their lithium-ion batteries. But keep in mind, if you need thermally conducive parts, a material can be developed.
There are low-cost composites, such as thermosets, but polymer composites are manufactured by a time-consuming process that slows down production rates. Another factor impacting costs: staff training is required for working with these advanced formulas and there are higher environmental and health issues at stake. The long-term gains will have to be considered against the upfront costs. The modulus of carbon fibres depends on the degree of perfection of the alignment.
Imperfections in alignment results in complex shaped voids elongated parallel to the fibre axis, which act as stress raisers and points of weakness. The alignment varies considerably with the manufacturing route and conditions. The layers have no regular stacking sequence, and the average spacing between the planes is 0. To obtain high modulus and strength, the layer planes of the graphite must be aligned parallel to the fibre axis [ 29 ].
Carbon fibres have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, and high temperature. The carbon fibres can be utilised in various applications such as aerospace, automotive, sporting goods, and consumer goods. Table 5 shows properties for the different grades of carbon fibre.
Indicative properties for the different grades of carbon fibre [ 27 ]. Kwolek is a DuPont chemist who in invented an aramid fibre known as Kevlar, the lightweight, stronger-than-steel fibre used in bulletproof vests and other body armour around the world. The chemical structure of the materials is being alternated aromatic aryl benzene rings and the amide CONH group.
The polymer is produced by the elimination of hydrogen chloride from terephthaloyl chloride and para-phenylene diamine. The polymer is washed and dissolved in sulphuric acid to form a partially oriented liquid crystal solution.
The solution is spun through small die holes, orientation taking place in the spinnerette, and the solvent is evaporated. Kevlar was introduced for commercial products in There are three principal types of Kevlar fibre as shown in Table 6. Characteristics of the different grades of aramid fibre [ 27 ]. Recently, with advantages of reasonable mechanical properties, low density, environmental benefits, renewability, and economic feasibility, natural fibres have been paid more attention to in composite applications.
The natural fibres in simple definition are fibres that are not synthetic or man-made and are categorized based on their origin from animals, mineral, or plant sources [ 30 ]. Natural fibres are one such proficient material which would be utilised to replace the synthetic materials and their related products for the applications requiring less weight and energy conservation. Natural plant fibres are entirely derived from vegetative sources and are fully biodegradable in nature.
Fibre-reinforced polymer matrix got considerable attention in numerous applications because of its good properties. The current indicators are that interest in natural fibre composites by the industry will keep growing quickly around the world. The application of natural fibre-reinforced polymer composites and natural-based resins for replacing existing synthetic polymer or glass fibre-reinforced materials is huge. However, natural fibre quality is influenced significantly by the age of the plant, species, growing environment, harvesting, humidity, quality of soil, temperature, and processing steps, and there is a move to reduce the on-field processing to improve consistency and reduce costs.
The properties of several natural fibres and commonly used synthetic fibres are shown in Table 7 [ 31 , 32 , 33 , 34 , 35 ]. Increasingly, the fibres have replaced parts formerly made of steel. The fibres used in composite materials appear at different forms and scales as shown in Figure 1.
Various fibre forms. There are several methods for fabricating composite materials. The selection of a method for a part will depend on the materials, the part design, the performance, and the end-use or application. Hand lay-up is an open contact moulding technique for fabricating composite materials. Resins are impregnated by the hand into fibres which are in the form of woven, knitted, stitched, or bonded fabrics.
In this technique, the mould is first treated with mould release, dry fibres or dry fabrics are laid on a mould, and liquid resin is then poured and spread onto the fibre beds [ 36 ].
This is usually accomplished by rollers or brushes, with an increasing use of nip-roller-type impregnators for forcing resin into the fabrics by means of rotating rollers and a bath of resin. A roller or brush is used to wet the fibres and remove air trapped into the lay-ups. A few layers of fibres are wetted, and laminates are left to cure under standard atmospheric conditions.
After these layers are cured, more layers are added, as shown in Figure 2. Hand lay-up process. Spray-up is also an open-mould application technique for composite. The spray lay-up technique is considered an extension of the hand lay-up method. In this process, the mould is first treated with mould release. If a gel coat is used, it is sprayed into the mould at a certain thickness after the mould release has been applied.
The gel coat then is cured, and the mould is ready for process. The fibre and catalysed resin at a viscosity of — cps are sprayed into the mould using a chopper spray gun. The gun chops continuous fibre tow into short-fibre bundle lengths and then blows the short fibres directly into the sprayed resin stream so that both materials are applied simultaneously on the surface of the mould, as shown in Figure 3.
In the final steps of the spray-up process, the workers compact the laminate by hand with rollers. The composite part is then cured, cooled, and removed from the mould [ 37 , 38 ]. The schematic of the spray lay-up process. Hand lay-up and spray-up methods are often used in tandem to reduce labour cost. This is a common process for making glass fibre composite products such as bathtubs, boat hulls and decks, fenders, RV components, shower stalls, spas, truck cabs, and other relatively large and noncomplex shapes.
With the ever-increasing demand for faster production rates, the industry has used alternative fabrication processes to replace hand lay-up as well as encouraged fabricators to automate those processes wherever possible. Resin transfer moulding RTM , sometimes referred to as liquid moulding, is a fairly simple process. In this technique, the mould is first treated with mould release. The dry reinforcement, typically a preform, is then placed into the mould and the mould is closed.
Low viscosity resin and catalyst are metered and mixed and then pumped into the mould under low-to-moderate pressure through injection ports, following predesigned paths through the preform.
Low-viscosity resin is used in RTM technique to ensure that the resin permeates through the preform quickly and thoroughly before gel and cure, especially with thick composite parts. Reaction injection moulding RIM injects a rapid cure resin and a catalyst into the mould in two separate streams. Mixing and chemical reaction occur in the mould instead of in a dispensing head. Automotive industry suppliers have combined structural RIM SRIM with rapid preforming methods to fabricate structural parts that do not require a class A finish.
Figure 4 describes the schematic of the RTM process [ 39 , 40 ]. The schematic of the RTM process. Representing the fastest-growing moulding technology is vacuum-assisted resin transfer moulding VARTM , as shown in Figure 5. VARTM technique does not require high heat or pressure. VARTM usually operates with low-cost tooling, making it possible to inexpensively produce large, complex parts in one shot [ 41 , 42 , 43 ].
Resin film infusion RFI is a hybrid process in which a dry preform is placed in a mould on top of a layer, or interleaved with multiple layers, of high-viscosity resin film.
Under applied heat, vacuum, and pressure, the resin liquefies and is drawn into the preform, resulting in uniform resin distribution, even with high-viscosity, toughened resins, because of the short flow distance.
Resin infusion has found significant application in boatbuilding. This method has been employed by The Boeing Co.
Figure 6 presents the schematic of the resin film infusion process. The schematic of the resin film infusion process. Compression moulding is a precise and potentially rapid process for producing high-quality composite parts in a wide range of volumes. The material is manually or robotically placed in the mould. The mould halves are closed, and pressure is applied using hydraulic presses.
Cycle time ranges depending on the part size and thickness. This process produces high-strength, complex parts in a wide variety of sizes. The composites are commonly processed by compression moulding and include thermosetting prepregs, fibre-reinforced thermoplastic, moulding compounds such as sheet moulding compound SMC , bulk moulding compounds BMC , and chopped thermoplastic tapes.
Figure 7 shows the schematic of the compression moulding process. The schematic of compression moulding process. Injection moulding is a closed process as shown in Figure 8. This is fast, high-volume, low-pressure, and most commonly used for filled thermoplastics, such as nylon with chopped glass fibre.
The injection-moulding process has been in use for nearly years. Reciprocating screw injection-moulding machines were introduced in the s and are still used today [ 45 ]. Injection speeds are typically one to a few seconds, and many parts can be produced per hour in some multiple cavity moulds.
Simplified diagram of moulding process. Filament winding is a continuous fabrication method that can be highly automated and repeatable, with relatively low material costs as shown in Figure 9. A long, cylindrical tool called a mandrel is suspended horizontally between end supports. Dry fibres are run through a bath of resin to be wetted. The fibre application instrument moves back and forth along the length of a rotating mandrel with the traverse carriage, placing fibre onto the tool in a predetermined configuration.
Computer-controlled filament-winding machines are used to arrange the axes of motion [ 46 , 47 , 48 ]. Filament winding is one example of aerospace composite materials. The schematic of the filament winding process. Composite pultrusion is a processing method for producing continuous lengths of fibre-reinforced polymer structural shapes with constant cross-sections.
This is a continuous fabrication method that can be highly automated. In this process, a continuous bundle of dry fibre is pulled through a heated resin-wetting station. The wetted bundle is pulled into heated dies, and the cross-sectional shape of the pulled fibre is formed by these dies. The resin is cured, and the composites are formed. Parts are then made by slicing the long-cured piece. This process is limited to straight parts with a constant cross-section, such as I-beams, T-beams, or frame sections and ladder rails.
Figure 10 shows the schematic of the pultrusion process [ 49 , 50 ]. Pultrusion is used in the manufacture of linear components such as ladders and mouldings.
The schematic of the pultrusion process. Automated fibre placement AFP is one of the most advanced methods for fabricating and manufacturing of composite materials as presented in Figure This method is used almost exclusively with continuous fibre-reinforced tape. A robot is utilised to place fibre-reinforced tape and build a structure one ply layer at a time.
A band of material comprised of multiple narrow strips of tape tows is placed where these tows are commonly 0. The use of robotics gives the operator active control over all the processes critical variables, making the process highly controllable and repeatable.
This method allows the fabrication of highly customised parts as each ply can be placed at different angles to best carry the required loads [ 51 , 52 ]. The schematic of the automated fibre placement process. Advantages of fibre placement are processing speed and reduced material scrap and labour costs. Often, the process is utilised to fabricate large thermoset parts with complex shapes. Similar to ATP process, automated tape laying ATL is an even speedier automated process in which prepreg tape, rather than single tows, is laid down continuously to form parts.
Additive manufacturing is also known as 3D printing technique. Additive manufacturing is a step change in the development of rapid prototyping concepts that were introduced more than 20 years ago. This is a process for making a solid object from a three-dimensional digital model, typically by laying down many successive thin layers of a material. Manufacturing a composite structure with a single nozzle uses polymer composite filament and contains polymer and additives such as rubber microspheres, particles of glass or carbon fibre, wood flour, etc.
This more recent form of composite part production grew out of efforts to reduce the costs in the design-to-prototype phase of product development, taking aim particularly at the material-, labour-, and time-intensive area of toolmaking [ 53 , 54 , 55 , 56 ]. The schematic of the 3D printing process for polymer composites. The polymer composite materials are lightweight, which increases the fuel efficiency of vehicles manufactured from composites and gives them structural stability.
In addition, they offer a high strength-to-weight ratio and increased heat resistance.
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