Weight is often a handicap for automotives, bicycles, motorcycles, aeronautics and ships: The heavier the body, the more energy is needed to move the vessel. Textiles combined with resins, commonly known as composites, enjoy a good reputation, when light weight, strength and design matter.
These are not the cheapest solutions at the moment, but their use can reduce the total costs during the life cycle of the product. Nevertheless, the technology has many applications where its high strength to weight ratio is of importance: aviation, naval industries, cars and bicycles. Improved manufacturing techniques are reducing the costs and time to manufacture, making it increasingly common in small consumer goods as well, such as laptop computers, tripods, fishing rods, paintball equipment, racquet sports frames, stringed instrument bodies, classical guitar strings and drum shells, Claudia Ollenhauer-Ries, our Special Correspondent from Germany, reports.
India saw a very spectacular car, the Caparo T1, at the Auto Expo in January 2008, of which a small quantity for the Asian market will be assembled at Caparo’s upcoming facility at Oragadom near Chennai. “The move represents a very big coup in India’s automotive history, as never before has a high-performance car with complex composite materials and construction techniques been assembled in India,” officials say.
[bleft]Five basic textile structures adopted are: conventional fabrics, non crimp fabrics (laid fibres), 3D-fabrics, overbraiding and tailored fibre placement[/bleft]
More recently, in early June 2008, Indian aviation giant Hindustan Aeronautics Limited (HAL) signed a contract with Israel. HAL will export lightweight composite materials, manufactured from carbon fibres, to Israel. While the composites are primarily intended for a new Israeli mini unmanned aerial vehicle (UAV) project, they will also be used for space applications, informed government sources. “Israel has outsourced its composite requirements for UAVs to India. The materials will be used for a mini UAV that will fly at an altitude of 10,000 feet,” a top Ministry of Defence official said. The composites, similar to the ones being used on India’s Advanced Light Helicopters and the Light Combat Aircraft, will significantly reduce the weight of the UAV to give it a longer range and an increased payload.
Pradip Thakkar, Chairman of the Fibre-Reinforced Plastic (FRP) Institute, Chennai, said at the Journal Exhibition Composites (JEC) 2008 in Paris/France, “All Indian composite industry is concerned. It is small, considering the European and Chinese market, but the Indian market is growing fast (20 to 25% in the automotive, transport and communication market)”.
Definition and Process
Composites are carbon fibre reinforced plastics (CFRP or CRP). Similar to glass-reinforced plastic, they are sometimes also known by the genericised trademark fibreglass, and the composite material is commonly referred to by the name of its reinforcing fibres (carbon fibre). Plastic is most often used as epoxy, a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or “hardener”. Other plastics, such as polyester, vinyl ester or nylon, are also sometimes used. Some composites contain both carbon fibre and other fibres such as Kevlar, aluminium and fibreglass reinforcement.
[bleft]CFRPs have found applications on construction of high-end audio components, musical instruments, etc. In firearms, it can substitute for metal, wood and fibreglass in many areas in order to reduce overall weight[/bleft]
The basic technology is having a textile structure which is draped into a 3-dimensional form. The 3D-shape is covered and impregnated with a fluid (resin, epoxy or other) material. This material is cured by pressure and chemical reaction. The result is a stable and light 3D-form. Any type of textile could be used: wovens, circular and warp knitted, flat knitted, braided and the latest 3D textile shapes like spacer fabrics could do as well as non wovens. Five basic textile technologies are adopted: conventional fabrics, non crimp fabrics (laid fibres), 3D-fabrics, overbraiding and tailored fibre placement.
The choice of matrix can have a profound effect on the properties of the finished composite. One method of producing graphite-epoxy parts is by layering sheets of carbon fibre cloth into a mould in the shape of the final product. The alignment and weave of the cloth fibres is chosen to optimize the strength and stiffness properties of the resulting material. The mould is then filled with epoxy and is heated or air cured. The resulting product part is very corrosion-resistant, stiff, and strong for its weight. Parts used in less critical areas are manufactured by draping cloth over a mould, with epoxy either preimpregnated into the fibres (also known as prepreg), or “painted” over it.
High performance parts using single moulds are often vacuum bagged and/or autoclave cured, because even small air bubbles in the material will reduce strength. The process in which most carbon fibre reinforced plastic is made, varies depending on the piece being created, the finish (outside gloss) required, and how many of this particular piece are going to be produced.
CFRP is a more costly material than its counterparts also used in the construction industry: Glass fibre reinforced polymer (GFRP) and Aramid fibre reinforced polymer (AFRP); though CFRP is generally regarded as having superior properties. Cost remains an issue and long- term durability questions still remain.
Preformed composites are 3D structures made by knitting, braiding and sewing. In addition, preform could be preimpregnated. A lot of R&D work is done internationally on this issue, as it could offer cost reduced parts ready to use.
Applications
Until recently, the fabric has had limited use in mass-produced cars because of the expenses involved in terms of material, equipment, and the relatively limited pool of individuals with expertise in working with it. Of late, several mainstream vehicle manufacturers have started to use CFRP in everyday road cars. Adopted by low-volume manufacturers, it is primarily being used for creating body-panels for their high-end cars due to its increased strength and decreased weight when compared to the glass-reinforced plastic.
Carbon fibre reinforced plastic has over the past two decades become an increasingly notable material used in structural engineering applications. Studied to explore its potential benefits in construction, it has also proved itself cost-effective in a number of field applications like strengthening concrete, masonry, steel and timber structures. Its use in industry can be either for retrofitting to strengthen an existing structure, or as an alternative reinforcing (or pre-stressing material) to steel from the outset of a project.
Retrofitting of the fabric is increasingly dominating in civil engineering, and applications include increasing the load capacity of old structures (such as bridges) that were designed to tolerate far lower service loads than they are today; seismic retrofitting and repair of damaged structures. Due to the incredible stiffness of CFRP, it can be used underneath bridge spans to help prevent excessive deflections, or wrapped around beams to limit shear stresses.
Carbon fibre reinforced plastic has found use in high-end sports equipment such as racing bicycles. For the same strength, a carbon fibre frame weighs less than a bicycle tubing of aluminium or steel. The choice of weave can be carefully selected to maximize stiffness. The variety of shapes it can be built into has further increased stiffness and also allowed aerodynamic considerations into tube profiles. Carbon fibre reinforced plastic frames, forks, handlebars, seat posts and crank arms are becoming more common on medium- and higher-priced bicycles.
Much of the fuselage of Boeing’s new 787 Dreamliner will be composed of CFRP, making the aircraft lighter than a comparable aluminium fuselage; with the added benefit of less maintenance, thanks to CFRP’s superior fatigue resistance.
CFRP has also found application in the construction of high-end audio components such as turntables and loudspeakers. It is used for parts in a variety of musical instruments, including violin bows, guitar pick guards, and a durable ebony replacement for bagpipe chanters. It is also used to create entire musical instruments such as Blackbird guitars carbon fibre rider models, Luis and Clark carbon fibre cellos and Mix carbon fibre mandolins.
In firearms, it can substitute for metal, wood and fibreglass in many areas in order to reduce overall weight.
Recycling
Carbon fibre reinforced plastics (CFRPs) have an almost infinite service life when protected from the sun. When it is time to decommission CFRPs, they cannot be melted down in air like many metals. When free of vinyl (PVC or polyvinyl chloride) and other halogenated polymers, CFRPs can be thermally decomposed via thermal depolymerization in an oxygen-free environment. This can be accomplished in a refinery in a one-step process. Capture and reuse of the carbon, and monomers is then possible.
CFRP’s can also be milled or shredded at low temperature to reclaim the carbon fibre; however this process shortens the fibres dramatically. Just as with down cycled paper, the shortened fibres cause the recycled material to be weaker than the original material. There are still many industrial applications that do not need the strength of full-length carbon fibre reinforcement. For example, chopped reclaimed carbon fibre can be used in consumer electronics, such as laptops. It provides excellent reinforcement of the plastics used even if it lacks the strength-to-weight ratio of an aerospace component.
Research & Design
Institut fuer Verbundwerkstoffe GmbH (IVW) is a non-profit research institute of the state Rhineland-Palatinate, Germany, exploring and advancing applications and potential applications of composite materials, based on polymer matrix systems. In 1990, the institute was founded on the campus of the University of Kaiserslautern and extended in 2002 by the Demonstrations- und Anwendungszentrum D.A.Z. IVW’s professors are lecturing different aspects on fibre-reinforced composite materials at the University of Kaiserslautern.
Basic idea regarding the projects at IVW is the consideration of the value-added chain “from the scientific basics to the component part” while integrating the core competencies of “Design and Analysis”, “Materials Science” and “Manufacturing Science”. Prof. (Dr.) Peter Mitschang works in the area of preformed structures. He reports: “A renaissance of the well-known resin injection moulding process occurs since several years. For this process the complete reinforcing structure is placed in the mould. After closing the mould this structure is impregnated by injecting the resin. By this process geometrically complex and large-area components in small to medium sized series can be manufactured economically.
Large potentials are offered for further rationalization of the LCM-process by using fibre semi-finished products (preforms), which are manufactured in a pre-process. Sewing approaches allow using high complex and integral textile preforms. Such preforms reduce the tool assembly complexity and offer the possibility of an automated and final net-shape manufacturing.” Dr. Peter’s department investigates on the influences of the sewing process or of the sewing thread on the part quality, and/or the characteristics of the components and the necessary mechanical technology is developed. A further increase of the functionality of textile preforms is reached by the integration of application joints.
Yet another German institute working on composites is the Institute for Textile and Apparel Technology (ITB) at Dresden. Many bilateral R&D projects with the industry cover the design and production of preformed composites.
NCC, Kettering, Ohio/USA an industry leader in developing innovative manufacturing methods, is using its signature Rapid Fibre Preform Process and its automated preform technology to produce a broad range of composite items. Used to manufacture the high quality preforms critical to successful closed moulding processes, the technology is based on the Programmable Powdered Preform Process (P4) created by Owens Corning and integrated at NCC.
One of the first organizations to make preforms with robots, NCC has refined the technique and advanced the use of robots at its headquarters and manufacturing facility to develop its unique Rapid Fibre Preform Process. Equipped with a two-station P4 preforming cell for the Automotive Composites Consortium (ACC), a single station P4 preforming cell modified for aerospace applications (P4A) and a single station performer (SSP) for commercial applications – NCC has used its Rapid Fibre Preform Process to produce a variety of items with dramatic results. The centre has also made significant advances with development projects using this process:
- Pick-up truck boxes realized a 33% weight savings with no cost increase when compared to the traditional steel structure.
- Composite fire helmets tested 15% lighter than SMC parts yet impact resistance was increased by 15%.
- Access door for a fighter aircraft generated a cost savings of 46% with a nine per cent reduction in weight when compared to other composite parts.
- Tailcone for jet transport netted a cost savings of 80% with a two per cent increase in weight when compared to composite assembly products.