Selection of composite?
There are two important principles that should apply to the selection of materials in the aerospace industry manufacturing:
· The material selection should be an integral part of the design process
· Materials selection should be numerate
It is therefore necessary to consider how the selection of composite can be made numerate We choose to do this by defining and describing all the individually important properties that composites are required to have and then categorizing the use of composite.
It has been estimated that there are more than 1000 materials available to designers and a correspondingly wide range of properties. Although the composite has been chosen primarily because it is able to satisfy the basic requirement for a property above all others.
Properties of Composites:
Composite materials are substances which contain 2 or more materials that combine to produce new substances with different physical properties from original substances.
Metal-Matrix Composites (mixtures of ceramics and metals)
Ceramic-Matrix Composites (Aluminium oxide and silicon carbide are materials that can be imbedded with fibers)
Polymer- Matrix Composites (Thermosetting resins are the most widely used polymers)
The above said are the classification system for composite materials.
The matrix material serves several functions in the composites. The most common example is the fiberglass, in which the glass fibers are mixed with a polymeric resin. If one had to cut the glass wool after proper surface preparation, the glass fibers and the polymer resin would be easy to distinguish. This is not the same as making an alloy by mixing two different materials together where the individual components become indivisible. An example of an alloy that most known is brass, consisting of a mixture of copper and zinc. After making the brass by melting the copper and zinc together and solidifying the resultant mixture, it is impossible to distinguish where the copper and zinc atoms are. There are many composites such as glass and epoxy, there are many other than cross-reinforced concrete (a mixture of steel rods and concrete (the same is made of rock and cement particles) (vulcanized plastic cords), many cheap plastics (polyurethane resin filled with ceramic particles such as chalk and talc) into composite exotic metal grids used in the space program, such as engine pistons (aluminium alumina filled with fibrous alumina). If independent of the actual compound, two (or more) components, the materials composing the composite material are always distinguished when the material is cut or broken. The composite materials can be classified according to the type of size and shape of the reinforcement. And, matrix is usually softer constituent of a composite. Usually stronger fundamental of a composite is reinforcement. Matrix is the last constituent to fail in fibre reinforced composites. The size range of dispersion in strengthened composite is between 0.01 to 0.1 µm. Rules of mixture provides upper and lower bounds for mechanical properties of particulate composites. Al-alloys for aerospace engine are reinforced to increase their wear resistance. Mechanical properties of fibre-reinforced composites depend on: – Properties of constituents, interface strength, fibre length, orientation and volume fraction. Longitudinal strength of fibre reinforced composite is mainly influenced by fibre strength. Polymers, cement and wood are the following materials can be used for filling in sandwich structures. Wood is not an example for laminar composite.
In brief, composite materials:
· Are Heterogenous
· Are Anisotropic
· Do not obey Hooke’s law
“One way or another we all want to fly. Whether it’s floating above the ground through the power of dreams.”
This research mainly concentrates on the details which have been tried and proven in aerospace composite design.
· Weight reduction,
· freedom of architectural
the above said features waves its path to use composites for aerospace industry. The primary ratio of composite materials selected for components is that of weight-saving for their relative stiffness and strength. These materials can withstand temperatures up to between 100 and 150 ° C (up to 250 ° C for resins. For example, the fibre-reinforced composite material may be five times stronger than the 1020 steel, and only has one-fifth of its weight. Aluminium (6061 degrees) is much closer to the weight of carbon fibre composite material, albeit even heavier, the composite can be double the meter and up to seven times the strength.
Composite plays many vital roles in automotive and aerospace industry. Composites can be moulded into variety of complex shapes without the need of high pressure tools. As is the case for all engineering materials, the composites have advantages and weaknesses which must be considered during the analyse step. However, an important driving force behind the development of composite materials is that the combination of reinforcement and matrix can be changed to satisfy the required final properties of an ingredient. For example, if the final component must be fire resistant, a fire-retardant matrix can be used in the growth stage to have this property. Finally, and by no means last, it should be emphasized that the field of composites is new to most long-standing engineers in most of the major aerospace companies and even though the engineers in may be highly competent in the design of metal aircraft structure they should accept (and benefit from) the fact that many new engineers are now available who possess a sound working knowledge and “Feel” for the use of composite materials.
There are four forces at work on any aeroplanes: lift thrust gravity and drag. Whether or not any aircraft will fly boils down to making sure the right balance between them. To overcome all the forces the aerospace machines got specific components. Example: Lift is provided by the wings, forward thrust comes from the engine. The real challenge lay in using the composites in the aerospace industry. Composite materials are extremely light weighted. Light weight and low maintenance have been the driving force for the integration of composites in the aerospace industry. Lighter vehicles, whether on roads or in the air, use less fuel and reduce carbon dioxide emissions. In addition to improved fuel efficiency and fuel economy, however, composite materials offer the added benefit of durable corrosion.
ü the body
ü the tail assembly
ü the wings
ü the landing gear assemblies
ü flight control systems and instruments
ü The powerplant /engine
The above said are six large subassemblies made with composites. The production of an aircraft is based on precise alignment and matching of each of the large subassemblies.
First step to lighter aeroplane
In the mid-1980s, the aerospace industry wanted to replace the complicated, expensive templates used to locate composite materials for the manufacture of airplane components. Made from fiberglass, standards can cost tens of thousands of pounds per piece for large pieces. This was the start for the growth. From there step by step development started. The report is written to carry out the components that have benefited the aerospace industry. The below mentioned graph would talk about the growth of materials in manufacturing aircrafts. Air craft wing manufacture
Airplane structures are designed with extreme attention in weight. The first aircraft had two wings of light wooden frames with fabric cloths, which are held by wires and beams. In the 1920s, metal began to be used for the structure of aircraft.
The metal wing is a box structure with skins consisting of:
· the top and bottom,
· Spars (front and back formed by I-beam)
· Ribs (internal structural parts running fore and aft in the wing)
· Stringers (in-out stiffeners)
The box structure can experience both tension and compression during turbulence air flow. Metal wings dramatically reduced the aerodynamic resistance that the aircraft managed to fly twice as fast with the same engine.
Then Air craft structures are made with carbon fibre epoxy composites. Carbon Fire epoxy are strong stiff and light weight material. They are formed by combining a supporting fiber and with resin matrix system such as epoxy. These combined composites are being a replacement for heavy metal wing. The major advantage is they can be assembled into larger not riveting structures. Strong molecular bonds of carbon-carbon chain give the fibers high strength to withstand forces. Polymer fibers such as polyacrylonitrile produce carbon fibers. Then carbon fibers are heated upto 1000 ° C with high tension is causing the formation to 2-dimensional carbon-carbon crystals when hydrogen is extracted.
Cost is the main barrier to the use of carbon composite fibers in aircraft. The autoclave method is more expensive due to the cost of capital equipment and the energy required for heating and pressure at 60 psi. Autoclave treatments cost £ 70.00 each and the curing of the oven used for CL2 was priced at £ 10.00 to reflect these differences in conditions.
Another element of cost is molds. These are usually made from Invar or other material with a very low thermal expansion coefficient in order that the curing process does not introduce size or shape differences.
The third major cost component is layup, which refers to the formation of uncured composite materials on the mold.
The fourth cost is reprocessing and repair. The composite components are made in layers and a significant failure in the separation or internal separation of the layers due to gas bubbles or insufficient connection. The parts and subassemblies at this stage are extremely rigid. If they do not fit properly, it is not possible to use the connectors to pull them together.
In the co-curing method, the uncured parts are placed on the surface on a carefully constructed mold, compressed together with a vacuum bag and placed in a large pressure vessel called autoclave. Then they are subjected to high pressure and high temperature while epoxy cures. In the welding process, the performed and pre-hardened parts are glued together with epoxide and the glued joints are cured with the use of the vacuum bag and the autoclave method.
Air craft wing structures are made to accurate shape and size. Then they will be tacked together to get the final product we want to achieve. There is greater saving in this process if the products are accurate. the holes of the aircraft must be substantially just opposite each other or else the fastener cannot fill the hole. Thousands of parts are made, and they are assembled by placing them in the correct place and fit drill holes with seals. Finally, fasteners are installed. If the holes are not accurate then the problem is harder to find and fix. This has been the biggest problem for many company. Answer for this problem is on its way. If this problem is solved the production cost will be low and making the components will be easy. This would lead us into Type 1 aircraft assembly.
Recent years the world has seen the advancement of design innovation at Aircraft wings. The transformation of airwings started since the Wright brother’s first plane. The use of composites has brought improvements in aerodynamic performances, weight reduction and efficiency on fuel saving. Composites brought 4%-5% fuel burn improvement and 4790 tonnes of CO2 per plane per year. In recent years there is increased investment in composites research and development. Over the past four years Broughton has invested over 400 million in production of air wings,
The investments do not provide an attractive rate of return for estimated investments.
Aeroplanes consists of a 40% weight distribution for the wing and 45% for fuselage. The manufacturing cost for these two large structures is about same range. Skin, Frames, Stringers are the main section that are manufactured using composites. The advance composite parts wave the path to reach the economical goal. And, to reduce the cost of manufacturing process as compared to aluminium fuselage. Before the designing process starts some mechanical elements must be taken to consideration:
· Forces produced by wings, empennage and landing gear.
· Inertia forces of components, loads and equipment
· Mass of Fuselage
· Air forces that run over the surface of the fuselage
· Pressure difference
The biggest that can we come across is the force which can create bending stress around fuselage structure.
Primary Structure- Passenger Area: This structure contains of two side shell and floor structure with circular skin which is twice the radius compared to the shell.
Secondary Structure- Cargo Department: The cargo compartment area is built with cargo platform
Obtaining cost-efficiency developed the concept of manufacturing shell. Greater fire resistance is critical in choosing the material. And, special attention is given for cost.
Manufacturing Process: – THE SINGLE LINE INJECTION (SLI)
This method is used in manufacturing primary structures. Specially shaped stainless-steel plates were used for the stiff parts that represent the aerodynamic surface. The detector layer consisted of a single layer of CFRP fabric and was placed directly on attached tooling. This manufacturing process will give best surface finish. synthetic fibers such as Aramid or Zylon is an option in order to attain higher resistance. The foam was used as a production aid. This allow a very easy setting of the shells. Considering the stiffness requirements, the strings were formed by wrapping the closed pore PMI foam with dry carbon fiber tubes and bands. They were placed next to each other The foam is mechanically processed with heat. The skin is placed on the wrapped tubes. Warp-knitted fabric is used. In order to obtain constant bending in the whole area, different thickness skin must be achieved by applying thinner foam cores. An aluminum tool was used to show contours. Vacuum-assisted resin infusion process was used to manufacture cargo components. Future Trends
1The pattern of using composite materials is constantly changing and the rate of change is constantly increasing. Having active polymer matrix composite materials since the 1980s, playing vital role till now. The flow of today’s complex growth causes changes within decades. there may also be changes in the criteria that determine if a material can be put into use on a large scale. In the past, these criteria were simply the availability of the basic complexes and technological skills of the chemist and engineer in turning them into useful items at an acceptable cost, leading to the present situation in which the most important material in terms of market size. And also the main goal for the future is to cut fuel consumption and CO2 emissions to provide more economical and “greener” air transport.
Key applications for the future include the LEAP engine featuring blades and a fan housing made of 3D woven RTM1 composite material. This ultimately leads to a weight reduction of nearly 450 kg for mid-range single-stroke aircraft. For knees, stratified composite materials reduce both weight and noise emissions.
Carbon fibre is weaved in 3D dimension for the full blade and made in complex shape. This would lead us into less turbulent flow, very light weight and work with more efficiency.