Composite Materials In Aircraft - Composite advantages In addition to the main benefit of reduced weight and formability, Composite materials offer better resistance to some forms of corrosion than metal alloys and good resistance to fatigue 'a crack in the brittle fiber is halted, temporarily at least, when it meets the
tougher resin matrix. Fuel consumption depends on several variables, including: dry aircraft weight, payload weight, age of aircraft, quality of fuel, air speed, weather, among other things. The weight of aircraft components made of composite materials are reduced by approximately 20%, such as in the case of the 787 Dreamliner.[4]
Composite Materials In Aircraft
The development of light-weight, high-temperature resistant composite materials will allow the next generation of high-performance, economic aircraft designs to materialize. Usage of such materials will reduce fuel consumption, improve efficiency and reduce direct operating costs of aircraft.
Fuel Savings With Reduced Weight[Edit | Edit Source]
Helicopters The excellent strength-to-weight ratio of composites is also used in helicopters to maximize payloads and performance in general. Boeing Vertol used composites for rotorcraft fairings in the 1950s and made the first composite rotor blades in the 1970s.
Composites are used in major structural elements of many modern helicopters, including the V22 tilt-rotor aircraft, which is approximately 50 percent composites by weight. The formability of composites has been used to particular advantage in helicopter manufacture to
reduce the number of component parts and therefore cost. The resin component in a composite serves to maintain fiber orientation, transfer loads, and to protect the structure against the environment. While a composite's stiffness, flexibility, and tensile strength are more affected by the reinforcement material, its heat resistance, shear and compressive strength are more dependent on the resin system.
Three types of resin systems are available: (1) polyesters, (2) vinyl esters, and (3) epoxies. All three require the user to mix a specific amount of hardener with a base chemical. The chemicals involved are shipped separately and combined only when the builder is ready to use the resin.
Conclusion[Edit | Edit Source]
Fabrication time Shorter assembly times, however, need to be offset against the greater time likely to be needed to fabricate the component in the first place. To produce a composite component, the individual layers, which are
often pre-impregnated ('pre-preg') with the resin matrix, are cut to their required shapes, which are all likely to be different to a greater or lesser extent, and then stacked in the specified sequence over a former (the former is a solid or framed structure used to keep
the uncured layers in the required shape prior to, and during, the curing process). This assembly is then subjected to a sequence of temperatures and pressures to 'cure' the material. The product is then checked thoroughly to ensure both that dimensional tolerances are met
and that the curing process has been successful (bubbles or voids in the laminate might have been formed as a result of contamination of the raw materials, for example). The last type of core material is honeycomb.
Factors Of Composite Material Usage[Edit | Edit Source]
This material has an appearance much like the honeycomb found in a beehive. The sheet material used to form honeycomb can be woven fabric, metal, or paper. Honeycomb cores are used very extensively in the aerospace industry.
Varying thicknesses are available along with a wide variety of materials. Honeycomb is usually supplied in 4 feet by eight feet sheets. Honeycomb materials offer exceptional strength to weight ratios but reliable bonding to outer skins is more difficult to achieve.
Polyurethane foam is basically a low-density insulating type foam also used for the construction of surf boards. Polyurethane foams are often used within a fuselage structure or for parts requiring detailed shaping. This type of foam is impervious to most solvents.
Its color is usually tan or green. Polyurethane foam has certain hazards. It emits a poisonous gas when burned. DO NOT USE A HOT WIRE DEVICE TO CUT POLYURETHANE FOAMS. You also do not want to burn any scraps of this type of foam.
Testing Of Composite Materials[Edit | Edit Source]
Carving and cutting should be accomplished using a knife, saw, or other cutting tools. Polyesters are most widely used for industrial applications and within the boat industry. They are cheap and they set up fast. A typical polyester is Bondo.
Polyesters are easy to mix with the amount of hardener added only affecting the time needed to develop full strength. Polyesters are not suitable for applications requiring high strength. They also will shrink over a period of time.
You may have noticed an automobile fender repair where the paint cracked over a period of time. Chances are Bondo was used as a filler and since it is a polyester it cracked under the paint.
In a few words, polyesters are the least capable resin for structural aircraft use. Beyond the day-to-day operating costs, the aircraft maintenance programs can be simplified by component count reduction and corrosion reduction. The competitive nature of the aircraft construction business ensures that any opportunity to reduce operating costs is explored and exploited wherever possible.
Ceramic Matrix Composites[Edit | Edit Source]
Fiberglass is the most common composite material, and consists of glass fibers embedded in a resin matrix. Fiberglass was first used widely in the 1950s for boats and automobiles. Fiberglass was first used in the Boeing 707 passenger jet in the 1950s, where it comprised about two percent of the structure.
Each generation of new aircraft built by Boeing had an increased percentage of composite material usage; the highest being 50% composite usage in the 787 Dreamliner. Whereas an aluminum wing has a known metal fatigue lifetime, carbon fiber is much less predictable (but dramatically improving every day), but boron works well (such as in the wing of the Advanced Tactical Fighter).
Aramid fibers ('Kevlar' is a well-known proprietary brand owned by DuPont) are widely used in honeycomb sheet form to construct very stiff, very light bulkhead, fuel tanks, and floors. They are also used in leading- and trailing-edge wing components.
Particulate composites CFRP and GFRP are fibrous composite materials; another category of Composite materials are particulate composites. Metal matrix composites (MMC) that are currently being developed for the aviation and aerospace industry are examples of particulate composites and consist, usually,
Hybrid Composite Steel Sheets[Edit | Edit Source]
of non-metallic particles in a metallic matrix; for instance silicon carbide particles combined with aluminum alloy. Spider silk is another promising material for composite material usage. Spider silk exhibits high ductility, allowing stretching of a fiber up to 140% of its normal length.[11]
Spider silk also holds its strength at temperatures as low as -40°C.[11] These properties make spider silk ideal for use as a fiber material in the production of ductile composite materials that will retain their strength even at abnormal temperatures.
Ductile composite materials will be beneficial to an aircraft in parts that will be subject to variable stresses, such as the joining of a wing with the main fuselage. The increased strength, toughness and ductility of such a composite will allow greater stresses to be applied to the part or joining before catastrophic failure occurs.
Synthetic spider silk based composites will also have the advantage that their fibers will be biodegradable. Composites have good tensile strength and resistance to compression, making them suitable for use in aircraft part manufacture. The tensile strength of the material comes from its fibrous nature.
When a tensile force is applied, the fibers within the composite line up with the direction of the applied force, giving its tensile strength. The good resistance to compression can be attributed to the adhesive and stiffness properties of the base matrix system.
It is the role of the resin to maintain the fibers as straight columns and to prevent them from buckling. The aerospace industry and manufacturers' unrelenting passion to enhance the performance of commercial and military aircraft is constantly
driving the development of improved high performance structural materials. Composite materials are one such class of materials that play a significant role role in current and future aerospace components. Composite materials are particularly attractive to aviation and aerospace applications because of their exceptional strength-
and stiffness-to-density ratios and superior physical properties. The A380 is about 20 to 22 percent composites by weight and also makes extensive use of GLARE (glass-fibre-reinforced aluminum alloy), which features in the front fairing, upper fuselage shells, crown and
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side panels, and the upper sections of the forward and aft upper fuselage. GLARE laminates are made up of four or more 0.38 mm (0.015 inch) thick sheets of aluminum alloy and glass fiber resin bond film.
GLARE offers weight savings of between 15 and 30 percent over aluminum alloy along with very good fatigue resistance. The top and bottom skin panels of the A380 and the front, center and rear spars contain CFRP, which
is also used for the rear pressure bulkhead, the upper deck floor beams, and for the ailerons, spoilers, and outer flaps. The belly fairing consists of about 100 composite honeycomb panels. Workshop Requirements Like most airplane building projects, if you have a space the size of a two-car garage you can start.
Ideally a room to do your actual "layup work" and another area or room in which to sand. You do not want the sanding particles to float around your fresh resin on your layers of fiberglass.
Good ventilation is necessary along with a way to somewhat control the temperature. Resins do not like cold temperatures. Remember you will need a workbench in addition to a worktable. The worktable should be large enough to cut your fiberglass and to assemble component parts.
A table 3 feet wide by up to 15-20 feet long is sometimes recommended. Remember to lay out your tools and your shop very neatly. This will save you a tremendous amount of time during the building process.
Carbon fiber or graphite is a very strong reinforcement material. It is used on sail boat masts, golf clubs, etc. Carbon fibers combine low weight, high strength, and high stiffness. In the custom aircraft area, carbon is used in critical areas such as spars, etc.
Working with carbon fiber is somewhat difficult and when it fails it will snap like a carrot snapping in two. Of course, the failure point where this occurs is extremely high. Building a composite airplane involves five stages of construction.
These five stages are (1) decision and planning, (2) basic building and assembly, (3) systems installation, (4) filling and finishing, and (5) inspection, certification, and final pre-flight. Decision and Planning Use of composites in aircraft design
Among the first uses of modern composite materials was about 30 years ago when boron-reinforced epoxy composite was used for the skins of the empennages of the U.S. F14 and F15 fighters. Initially, Composite materials were used only in secondary structures, but
as knowledge and development of the materials has improved, their use in primary structures such as wings and fuselages has increased. The sidebar on page 15 lists some aircraft in which significant Amounts of composite materials are used in the airframe.
Composite materials are used extensively in the Eurofighter: the wing skins, forward fuselage, flaperons and rudder all make use of composites. Toughened epoxy skins constitute about 75 percent of the exterior area. In total, about 40 percent of the structural weight
of the Eurofighter is carbon-fibre-reinforced composite material. Other European fighters typically feature between about 20 and 25 percent composites by weight: 26 percent for Dassault's Rafael and 20 to 25 percent for the Saab Gripen and the EADS Mako.
Adam Quilter is head of the strength analysis group, ESDU International (an IHS company) ESDU International provides validated engineering design data, methods and software for the engineer. These are presented in over 1340 design guides with supporting software and are the result
of more than 60 years experience of providing engineers with information, data and techniques for fundamental design and analysis. ESDU data and software form an important part of the design operation of companies large and small throughout the world.
The A340-500 and 600 feature additional composite structures, including the rear pressure bulkhead, the keel beam, and some of the fixed leading edge of the wing. The last is particularly significant, as it constitutes the first large-scale use of a thermoplastic matrix
composite component on a commercial transport aircraft. Composites enabled a 20 percent saving in weight along with a lower production time and improved damage tolerance. Weight is everything when it comes to heavier-than-air machines, and designers have strived continuously to improve lift to weight ratios since man first took to the air.
Composite materials have played a major part in weight reduction, and today there are three main types in use: carbon fiber-, glass-, and aramid-reinforced epoxy.; there are others, such as boron-reinforced (itself a composite formed on a tungsten core).
Within the sport aviation world, the term "composite aircraft" is synonymous with sleekness of design and speed. These airplanes, composed largely of fiberglass, are becoming more and more popular. Certainly when we attend a large fly-in we see rows and rows of composite aircraft.
To many of us these airplanes are somewhat mysterious. How are they built? What does the word "composite" actually mean? Are they safe? How difficult are they to build? A word of caution. The specifications for the materials to be used for your airplane should be stated within your plans or provided with your kit.
It is important that you conform to the plans of the designer. Composite materials can be formed into various shapes and, if desired, the fibers can be wound tightly to increase strength. A useful feature of composites is that they can be layered, with the fibers in each layer running in a different direction.
This allows an engineer to design structures with unique properties. For example, a structure can be designed so that it will bend in one direction, but not another.[2] Complex shapes Another advantage of composite materials is that, generally speaking,
they can be formed into more complex shapes than their metallic counterparts. This not only reduces the number of parts making up a given component, but also reduces the need for fasteners and joints, the advantages
of which are twofold: fasteners and joints may be the weak points of a component 'a bolt needs a hole which is a stress concentration and therefore a potential crack-initiation site, and fewer fasteners and joints can mean a shorter assembly time.
Polyvinyl chloride foams (PVC) are based on the same chemistry used in common PVC water pipe material. Divinycell and Klegecell are tradenames for this type of foam. Both of these are suited for structural cores. This material is resistant to most solvents and it can withstand a high temperature.
The types have different mechanical properties and are used in different areas of aircraft construction. Carbon fiber, for example, has unique fatigue behavior and is brittle, as Rolls-Royce discovered in the 1960s when the innovative RB211 jet engine with carbon fiber compressor blades failed catastrophically due to bird strikes.
A major disadvantage about the use of composites is that they are a relatively new material, and as such have a high cost. The high cost is also attributed to the labor intensive and often complex fabrication process.
Composites are hard to inspect for flaws, while some of them absorb moisture. Kevlar is a product of the DuPont Corporation. It is a very tough material with a high strength. It is used in making bulletproof vests.
Kevlar is very effective in applications requiring resistance to abrasion and puncture. However, its use in primary structures is often limited by the relatively low compression strength and difficulty in handling. Actually, composite aircraft construction is not a new idea.
Gliders have been constructed using fiberglass for many years. Throughout aviation history, advances in design have been made. Beginning with wooden structures that were covered with fabric, technology then advanced to welded steel frameworks and on to aluminum.
As each type of construction was introduced, design improvements were made in strength and aircraft performance. Composite construction is yet another advancement for the aircraft industry. Fiberglass construction has been and continues to be used in manufacturing a number of parts found on most airplanes.
Of course we now see many airplanes that are constructed almost exclusively out of composite material. Composite technology has certainly changed the entire aviation industry and in particular sport aviation. Choosing the proper core material is critical to the overall composite's performance.
Note the illustration in figure 1. The first item is one piece of material with its respective weight and strength being shown as 1.0. When we insert a core material doubling the thickness of the composite notice that the strength increases to 3.5 the stiffness to 7.0 but the weight only increases by 3%.
Further strength is noted by increasing the thickness 4 times. Observe even in this case the weight only increases by 6%.
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