Hardeners include aliphatic amines, cycloaliphatic amines, polyamides, aromatic amines, anhydrides, phenols, thiols and latent hardeners e. Many aerospace applications use amine-cured, multifunctional epoxies that require cure at elevated temperatures and pressures.
Toughened epoxy — with thermoplastics and reactive rubber compounds added to counteract brittleness due to high degree of crosslinking — have become the norm in high percentage composite airframes, such as The Boeing Co.
A notable development on the epoxy front, powered in large part by the automotive industry's enduring expectation of "part-per-minute" production, has been the advent of a group of new resin formulations that have acquired the apt descriptor "snap-cure" epoxies.
It's the collective term for resins designed with an out-life similar to conventional epoxies, which can be prolonged until fibers are thoroughly impregnated, but then, at a "trigger" temperature, can be activated to a cure cycle with a duration of two minutes or less. Hexion Inc. Columbus, OH, US has offered a range of optimized fast-cure epoxies, curing agents and preform binders.
The combination reportedly results in a part-to-part cycle time of less than 1 minute, depending on part size and complexity. The low tack of HexPly M77 enables the prepreg to be cut into precise shapes by laser cutter, then robotically oriented, assembled and consolidated into flat preforms. Bio-based epoxies are also being developed by a number of firms. One is Sicomin Chateauneuf les Martigues, France that has developed several trademarked GreenPoxy resins for a decade.
Entropy claims the resin adheres well to reinforcements and has better elongation properties than petroleum-based epoxies. Phenolic resins are based on a combination of an aromatic alcohol and an aldehyde, such as phenol, combined with formaldehyde. They find application in flame-resistant aircraft interior panels and in commercial markets that require low-cost, flame-resistant and low-smoke products.
Excellent char yield and ablative heat-absorbing characteristics have made phenolics long-time favorites for ablative and rocket nozzle applications. They also have proven to be successful in nonaerospace applications, notably in components for offshore oil and gas platforms, and in mass transit and electronics applications.
However, phenolics polymerize by means of a condensation reaction, which causes the release of water vapor and formaldehyde during cure. This phenomenon can produce voids in the composite. For that reason, phenolics are not typically processed using RTM. Cyanate esters CEs are versatile matrices that provide excellent strength and toughness, allow very low moisture absorption and possess superior electrical properties compared to other polymer matrices, although these benefits come at a higher cost.
Current applications range from radomes, antennae, missiles and ablatives to microelectronics and microwave products. Among the more exotic of resins, bismaleimides and polyimides close relatives, chemically are used in high-temperature applications on aircraft and missiles e. Volatiles and moisture emitted during cure make polyimides more difficult to work with than epoxies or CEs; special formulation and processing techniques have been developed to reduce or eliminate voids and delamination.
Both BMIs and polyimides have traditionally exhibited higher moisture absorption and lower toughness values than CEs and epoxies, but significant progress has been made in recent years to create tougher formulations, and BMIs are now touted as having better resistance to fluid ingression than epoxies.
This is the reason behind much of its use on the F Lightning II , enabling damage-tolerant structures at lower mass vs. Benzoxazines are formed by reacting phenol, formaldehyde and amine in an additive reaction with ring opening polymerization which produces a high molecular weight polymer with near-zero cure shrinkage, reactive sites that greatly facilitate hybridizing with other resins, and the ability to polymerize with itself homopolymerize to form polybenzoxazine networks very similar to phenolic.
Interest in benzoxazines is increasing due to its high stiffness, excellent thermal properties, lower moisture absorption, better resistance to flammability and also to ultraviolet UV radiation than epoxies. Like BMI, these higher-T g systems can be brittle and need to be toughened to prevent microcracking. Suppliers claim that they can be processed in much the same way same as epoxies but with a lower heat reaction.
Benzoxazine has a price point and achieves performance between that of epoxy and BMI. How it is presented to the potential user varies, however, based on the very different approaches taken by its two leading suppliers. Henkel — supplying structural prepregs, infusion resins and film adhesives, while partnering with Airtech International Inc. Huntington Beach, CA, US to offer tooling prepreg — sees benzoxazine as a way to cut the cost of composite structures throughout the supply chain due to its room-temperature stability no frozen storage and processing advantages, satisfying not just complex structural demands, but also supply, handling, surface finish and health and safety requirements.
Offering the flammability, smoke and toxicity FST performance of phenolic without its voids and processing difficulties, benzoxazine seems poised to push large, integrated structures into aircraft and other transportation interiors. Wood, a natural composite, is a combination of cellulose or wood fibers and a substance called lignin. The fibers give wood its strength; lignin is the matrix or natural glue that binds and stabilizes them.
Other composites are synthetic man-made. Plywood is a man-made composite that combines natural and synthetic materials. Thin layers of wood veneer are bonded together with adhesive to form flat sheets of laminated wood that are stronger than natural wood. Not all plastics are composites. In fact, most plastics—the ones used in toys, water bottles and other familiar items—are not composites. By Hammat H. Valiev, Alexander N.
Vlasov, Vyacheslav V. Vorobyev, Yuliya N. Karnet, Yury V. Kornev and Oleg B. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals.
Dawoud and Hosam M. Downloaded: Well-known examples of composite materials are as follows: Lignocellulosic straw in sludge Wood cellulose fibers embedded in hemicellulose and the binder lignin Bones soft protein collagen combined with the hard mineral apatite Pearlite ferrite combined with cementite [ 3 , 4 ] Classification of composite materials occurs at two different levels: The first criterion of classification is based on the matrix binder constituent.
A range of other classifications of composite materials exist as follows: Classification according to the type of matrix materials: Metal matrix composites MMCs Metal fibers are generally of low costs but have a relatively high specific mass. Inorganic nonmetallic matrix composite materials. Polymer matrix composites PMCs. Elongation at break is lower than observed for glass fibers. Minimal thermal expansion, sometimes even thermal contraction.
Drastically higher fatigue resistance than glass. Electrical conductive. A hundred times more expensive than glass. High anisotropy. Preparation modes: Polymer pyrolysis: the currently most frequently used method; resorts to synthetic polymers like polyacrylonitrile PAN or to natural polymers. Hydrocarbon pyrolysis: even production of nanofibers is possible.
Glass fiber composites. Organic fiber composites. Boron fiber or SiC fiber composites. Table 1. More Print chapter. How to cite and reference Link to this chapter Copy to clipboard. Cite this chapter Copy to clipboard Mohamed M. Saleh November 5th Available from:. Over 21, IntechOpen readers like this topic Help us write another book on this subject and reach those readers Suggest a book topic Books open for submissions. More statistics for editors and authors Login to your personal dashboard for more detailed statistics on your publications.
Access personal reporting. Dishes, Solar Booms and Solar Arrays, etc. Longerons, etc. Tanks, Other Pressurised Systems, etc. Baggage Racks and Several Similar Applications. Bicycle Frames, etc. Polymer composites are used normally up to 0 C, but rarely beyond 0 C. The high temperature capabilities of inorganic reinforcements cannot be realized, when polymers are employed as matrix materials.
Metal matrices, on the other hand, can widen the scope of using composites over a wide range of temperatures. Besides, metal matrix composites allow tailoring of several useful properties that are not achievable in conventional metallic alloys. High specific strength and stiffness, low thermal expansion, good thermal stability and improved wear resistance are some of the positive features of metal matrix composites.
The metal composites also provide better transverse properties and higher toughness compared to polymer composites. The reinforcements can be in the form of either particulates, or short fibres or continuous fibres. The thermo-mechanical properties of some common matrices are presented in Table 2. The composites with aluminium matrices are relatively lightweight, but their applications are limited to the lower temperature range.
GPa Coefficient. Titanium and nickel can be used at a service temperature of up to 0 C. There are several systems such as engine components which are exposed to high level of temperature. Titanium and nickel composites are ideal for such situations, as they retain useful properties at 0 C. Ti-6AL-4V is the commonly used titanium matrix material. The other alloys of titanium include ATi, ATi, etc. Molybdenum is a high temperature matrix and fibre material. Iron and steel matrices are cheaper and can be used at high temperatures, if the weight is not the major concern.
The high temperature applications of metal matrix composites are listed in Table 2. The material cost is the major problem that currently limits their uses, otherwise most of the metallic structural parts can be replaced with metal matrix composite parts to gain advantages. Valves, Fins. Ceramic provide strength at high temperature well above 0 C and have considerable oxidation resistance. However, the major drawback of ceramics is that they exhibit limited plasticity.
This low strain capability of ceramics is of major concern, as it, quite often, leads to catastrophic failure. For this reason ceramics are not considered as dependable structural materials. But such limitations may not exist with ceramic matrix composites, as suitable reinforcements may help them to achieve desirable mechanical properties including toughness.
The reinforcements which are normally high temperature inorganic materials including ceramics, may be in the form of particles, flakes, whiskers and fibres. The commonly used fibres are carbon, silicon carbide, silica and alumina. The current resurgence in the research and development of ceramic matrix composites is due to their resistance to wear, creep, low and high cycle fatigue, corrosion and impact combined with high specific strength at high temperatures.
The cutting rate of an alumina-SiC whisker cutting tool is ten times higher than that of conventional tools. The use of ceramic composites in aero-engine and automotive engine components can reduce the weight and thereby enhance the engine performance with higher thrust to weight ratios due to high specific strength at high temperatures. Automotive engines exhibit greater efficiency because of their low weight, better performance at high operating temperatures and longer life time due to excellent resistance to heat and wear.
Several high temperature applications of ceramic matrix composites are presented in Table 2. Carbon-carbon composites are the most important class of ceramic matrix composites that can withstand temperatures as high as 0 C. They consist of carbon fibres distributed in a carbon matrix. They are prepared by pyrolysis of polymer impregnated carbon fibre fabrics and preforms under pressure or by chemical vapour deposition of carbon or graphite.
The polymers used are of three types: thermosets furfurals, phenolics , thermoplastic pitches coal tar based and petroleum based and carbon-rich vapours hydrocarbons such as methane, propane, acetylene, benzene.
Phenolic resins are more commonly used in the manufacturing process of carbon-carbon composites. The phenolic resin impregnated carbon fibre preforms, on pyrolysis, converts the phenolic resin to a high proportion of amorphous carbon char.
The composite material is found to be porous after the first pyrolysis. It is further impregnated with the phenolic resin and pyrolised, usually under vacuum and pressure, and the process is repeated several times to reduce the void content and realize the optimum density of the material.
The major advantage of carbon-carbon composite is that various fabrics and shapes of preforms with multidirectional fibre alignments can be impregnated with resins and pyrolised to yield a wide class of one directional 1D , two directional 2D , three directional 3D and multidirectional composite blocks of various shapes and sizes, which can be machined to produce the desired dimensions.
Excellent wear resistance, higher coefficient of friction with the rise of temperature, high thermal conductivity, low thermal expansivity and high temperature resistance make them useful materials in high temperature applications. In absence of oxygen, carbon-carbon composites can withstand very high temperatures 0 C or more for prolonged periods.
They are also used in prosthetics due to excellent biocompatibility. The structural applications of composites are mostly in the form of laminates. Laminates provide the inherent flexibility that a designer exploits to choose the right combination of materials and directional properties for an optimum design. A lamina is the basic building block in a laminate. A lamina may be made from a single material metal, polymer or ceramic or from a composite material.
A composite lamina, in which all filaments are aligned along one direction parallel to each other, is called a unidirectional lamina.
Some unidirectional laminae are illustrated in Fig. Here the fibres continuous are oriented along a direction parallel to the x 1 axis. Note that the x 1 ' , x 2 ' axes are the material axes, and the x 1, x 2 axes are the reference axes.
The orientation of the fibre with respect to the reference axis i. A laminate is designated by the manner laminae are stacked to form the laminate. Unless it is specified, it is normally assumed that all the laminae in a laminate possess the same thickness. A cross-ply laminate consists of only 0 0 and 90 0 laminae. A laminate may be considered symmetric, antisymmetric or unsymmetric, in case there exists, with respect to the middle surface, any symmetry, antisymmetry or unsymmetry, respectively.
Figures 2. It has symmetry about the midsurface of the laminate. An unsymmetry may also be introduced by stacking laminae made of different composites. Various such hybrid laminates can be prepared for practical applications choosing various combinations of layers of metallic materials, polymer composites, metal-matrix composites and ceramic composites.
Aramid epoxy composites are commonly combined with carbon epoxy composites to make carbon-kevlar hybrid composites to obtain a cost effective composite with superior compressive and impact resistant properties. Kevlar fibres are inexpensive compared to carbon fibres and are effective in resisting the impact forces. Carbon fibres, in turn, improve the compressive strength in the carbon-kevlar hybridization. Why fibres are preferred to other reinforcements?
What are whiskers? Describe how fibres are fabricated using vapour deposition processes. What are carbon-carbon composites and how they are produced? Why they are recommended for high temperature applications? Write a note on metal matrix composites.
Write a note on ceramic matrix composites. Describe the characteristics of a couple of thermosets and thermoplastics that are used for making composites for aerospace applications. Why Kevlar fibres are recommended for strength and impact based structural designs? What are the basic differences between organic and other fibres? Fibre Material. Tensile strength MPa. Tensile modulus GPa. Silica SiO 2. Boron carbide B 4 C. Boron nitride. Silicon carbide SiC. TiB 2.
Zirconium oxide. Alumina Al 2 O 3. Alumina FP. Quartz whisker. Fe whisker. SiC whisker. Al 2 O 3 whisker. BeO whisker. B 4 C whisker. Si 3 N 4 whisker. Graphite whisker. Melting point 0 C. Kelvar Quartz Whisker. Ultra high Modulus. Polyether ether ketones PEEK. Polyphenylene sulfide. Tensile strength, MPa.
Tensile modulus, GPa. Maximum service temperature, K. Service temperature, K. Marine and Mechanical. Aluminium and alloys.
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