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  1. 1. COMPOSITE MATERIALS HISTORY  The earliest man-made composite materials were straw and mud combined to form bricks for building construction. Ancient brick- making was documented by Egyptian tomb paintings.  Wattle and daub is one of the oldest man-made composite materials, at over 6000 years old. Concrete is also a composite material, and is used more than any other man-made material in the world.  Woody plants, both true wood from trees and such plants as palms and bamboo, yield natural composites that were used prehistorically by mankind and are still used widely in construction and scaffolding.  Plywood 3400 BC by the Ancient Mesopotamians; gluing wood at different angles gives better properties than natural wood.  Cartonnage layers of linen or papyrus soaked in plaster dates to the First Intermediate Period of Egypt c. 2181–2055 BC and was used for death masks.  Papier-mâché, a composite of paper and glue, has been used for hundreds of years. The first artificial fiber reinforced plastic was Bakelite which dates to 1907, although natural polymers such as shellac predate it WHAT ARE THEY? A composite material can be defined as a macroscopic combination of two or more distinct materials, having a recognizable interface between them. Materials which differ by their nature or origin are combined in order to take benefit from their different properties. Composite materials are widely presented in the nature (e.g. wood, bones...) and also designed and produced by humans (e.g. concrete, reinforced plastics, plywood ...). For technical applications, the definition can be restricted to include only those materials that contain a reinforcement (such as fibers or particles) supported by a binder (matrix) material. According to their performance and properties, composite materials may also be classified as:
  2. 2.  General purpose composites  Advanced composites. Composites used for aircraft structures are mainly classified as advanced composites. ADVANCED COMPOSITES IN AIRCRAFT INDUSTRY Applications of composites on aircraft include:  Fairings  Flight control surfaces  Landing gear doors  Leading and trailing edge panels on the wing and stabilizer  Interior components  Floor beams and floor boards  Vertical and horizontal stabilizer primary structure on large aircraft  Primary wing and fuselage structure on new generation large aircraft  Turbine engine fan blades  Propellers These Advanced Composites combine high strength or high modulus continuous fibers (as reinforcement) and a high performance matrix system. The most common fiber types are:  GLASS  CARBON  ARAMID The most common matrix types are resins like:  EPOXYDE  PHENOLIC For some applications, Thermoplastics are also used. CRITERIA FOR COMPOSITE MATERIALS CHOICE Composites are used because of their:
  3. 3.  Low weight  High strength  High stiffness  Non sensitivity to corrosion  Fatigue behavior They also allow:  A reduction in the member of structure parts  The building of complex curved shapes  A good surface finish But also some disadvantages, compared with metal, have to be taken into account:  Material cost  Production cost  Need for lightning strike protection  Need for a lightning protection  Need for an antistatic protection (not for carbon) MATRIX MATERIALS MATRICES USED IN ADVANCED COMPOSITES The purpose of the composite matrix is to bind the fibers together by virtue of its cohesive and adhesive characteristics to:  Transfer the loads to and between fibers.  Provide the required protection to the reinforcement,  Maintain the shape and geometry of the component. Depending on the application (level of strength or rigidity, overall service temperature, chemical environment compatibility with fibers, fire or toxicity requirements and also: cost, processability.) the matrix will be either organic, metallic or ceramic. Organic matrices, commonly called resins, combined with long fiber reinforcements, constitute the majority of applications in advanced composites.
  4. 4. Resin types used are divided in two families:  THERMOPLASTIC  THERMOSETTING Their molecular structure is completely different and therefore their properties and behavior are different. The selection will depend on the application and the environment. THERMOPLASTIC MATRIX: These materials are hard at ambient temperature and become malleable when heated. During the heating process there is no chemical reaction and therefore the transformation is reversible. The manufacturing process for molding requires heating, above the melt temperature, and cooling down. The heating and cooling can be repeated several times without damaging the material. There is no ageing process of the raw material before transformation and therefore the raw material does not require a particular storage, except a dust free and dry environment. Several types of thermoplastics are available in the industry. 1. Semicrystalline Thermoplastics Semicrystalline thermoplastics possess properties of inherent flame resistance, superior toughness, good mechanical properties at elevated temperatures and after impact, and low moisture absorption. They are used in secondary and primary aircraft structures. Combined with reinforcing fibers, they are available in injection molding compounds, compression-moldable random sheets, unidirectional tapes, prepregs fabricated from tow (towpreg), and woven prepregs. Fibers impregnated in semicrystalline thermoplastics include carbon, nickel-coated carbon, aramid, glass, quartz, and others. 2. Amorphous Thermoplastics Amorphous thermoplastics are available in several physical forms, including films, filaments, and powders. Combined with reinforcing fibers, they are also available in injection molding compounds, compressive moldable random sheets, unidirectional tapes, woven prepregs, etc. The fibers used are primarily carbon,
  5. 5. aramid, and glass. The specific advantages of amorphous thermoplastics depend upon the polymer. Typically, the resins are noted for their processing ease and speed, high temperature capability, good mechanical properties, excellent toughness and impact strength, and chemical stability. The stability results in unlimited shelf life, eliminating the cold storage requirements of thermoset prepregs. 3. Polyether Ether Ketone (PEEK) Polyether ether ketone, better known as PEEK, is a high temperature thermoplastic. This aromatic ketone material offers outstanding thermal and combustion characteristics and resistance to a wide range of solvents and proprietary fluids. PEEK can also be reinforced with glass and carbon. THERMOSETTING MATRIX: These resin systems are in a liquid or a paste state at room temperature before transformation. They require to be cured for polymerisation. The polymerisation is a non-reversible chemical reaction between a resin base and a hardener. Each Thermosetting material has its own curing cycle, which has been qualified to meet the minimum required properties. It is important to note that Thermosetting materials have a limit shelf life when not cured. In order to limit the ageing effect it is required to store them at low temperature. There are several types such that: 1. Polyester Resins Polyester resins are relatively inexpensive, fast processing resins used generally for low cost applications. Low smoke producing polyester resins are used for interior parts of the aircraft. Fiber- reinforced polyesters can be processed by many methods. Common processing methods include matched metal molding, wet layup, press (vacuum bag) molding, injection molding, filament winding, pultrusion, and autoclaving.
  6. 6. 2. Vinyl Ester Resin The appearance, handling properties, and curing characteristics of vinyl ester resins are the same as those of conventional polyester resins. However, the corrosion resistance and mechanical properties of vinyl ester composites are much improved over standard polyester resin composites. 3. Phenolic Resin Phenol-formaldehyde resins were first produced commercially in the early 1900s for use in the commercial market. Ureaformaldehyde and melamine-formaldehyde appeared in the 1920–1930s as a less expensive alternative for lower temperature use. Phenolic resins are used for interior components because of their low smoke and flammability characteristics. 4. Epoxy Epoxies are polymerizable thermosetting resins and are available in a variety of viscosities from liquid to solid. There are many different types of epoxy, and the technician should use the maintenance manual to select the correct type for a specific repair. Epoxies are used widely in resins for prepreg materials and structural adhesives. The advantages of epoxies are high strength and modulus, low levels of volatiles, excellent adhesion, low shrinkage, good chemical resistance, and ease of processing. Their major disadvantages are brittleness and the reduction of properties in the presence of moisture. The processing or curing of epoxies is slower than polyester resins. Processing techniques include autoclave molding, filament winding, press molding, vacuum bag molding, resin transfer molding, and pultrusion. Curing temperatures vary from room temperature to approximately 350 ° F (180 °C). The most common cure temperatures range between 250° and 350 °F (120–180 °C). 5. Polyimides Polyimide resins excel in high-temperature environments where their thermal resistance, oxidative stability, low coefficient of thermal expansion, and solvent resistance benefit the design. Their
  7. 7. primary uses are circuit boards and hot engine and airframe structures. A polyimide may be either a thermoset resin or a thermoplastic. Polyimides require high cure temperatures, usually in excess of 550 °F (290 °C). Consequently, normal epoxy composite bagging materials are not usable, and steel tooling becomes a necessity. Polyimide bagging and release films, such as Kapton® are used. It is extremely important that Upilex® replace the lower cost nylon bagging and polytetrafluoroethylene (PTFE) release films common to epoxy composite processing. Fiberglass fabrics must be used for bleeder and breather materials instead of polyester mat materials due to the low melting point of polyester. 6. Polybenzimidazoles (PBI) Polybenzimidazole resin is extremely high temperature resistant and is used for high temperature materials. These resins are available as adhesive and fiber. 7. Bismaleimides (BMI) Bismaleimide resins have a higher temperature capability and higher toughness than epoxy resins, and they provide excellent performance at ambient and elevated temperatures. The processing of bismaleimide resins is similar to that for epoxy resins. BMIs are used for aero engines and high temperature components. BMIs are suitable for standard autoclave processing, injection molding, resin transfer molding, and sheet molded compound (SMC) among others. Thermosetting resins use a chemical reaction to cure. There are three curing stages, which are called A, B, and C. o A stage: The components of the resin (base material and hardener) have been mixed but the chemical reaction has not started. The resin is in the A stage during a wet layup procedure. o B stage: The components of the resin have been mixed and the chemical reaction has started. The material has thickened and is tacky. The resins of prepreg materials are in the B stage. To prevent further curing the resin is placed in a freezer at 0 °F. In the frozen state, the resin of the prepreg material stays in the B
  8. 8. stage. The curing starts when the material is removed from the freezer and warmed again. o C stage: The resin is fully cured. Some resins cure at room temperature and others need an elevated temperature cure cycle to fully cure. REINFORCEMENT MATERIALS REINFORCEMENT IN ADVANCED COMPOSITES In advanced composite design, different types of reinforcement materials are used. They are used in combination with a selected matrix, to build up the composite. Mainly two types of fiber are used:  short fibers (non-continuous reinforcement)  long fibers (continuous reinforcement) The fibers are embedded in the matrix to meet the design requirements (loads, environment, weight ...). When a design requires load transfer and weight saving, long fibers are used. The reinforcement is made of tows which are an arrangement of thousands of filaments of a diameter between 4 and 15 micro meters. Three kinds of reinforcements are used advanced composites on commercial aircraft:  GLASS  ARAMID  CARBON To select the appropriate fiber many parameters should be noted such that:  Mechanical properties (strength and modulus) in direction of the filaments in tensile and compression.  Weight.  Thermal expansion.
  9. 9.  Processability SEMI FINISHED PRODUCTS In the aircraft industry, the most commonly used semi-finished products are: TOWS/YARNS A tow is an untwisted bundle of continuous filaments made of carbon, glass or aramid. A tow designated as 3K has 3000 filaments. A yarn is an assembly of twisted filaments to form a continuous length that is suitable for use in weaving or interweaving into textile material. This product is used in filament winding process. The dry tow is dipped in liquid resin and applied on a mandrel. TAPES This product is an arrangement of parallel tows in a single direction. The mechanical properties are provided only in the direction of the fiber. They are available on the market in prepreg form only. FABRICS
  10. 10. This product is made of woven tows or yarns in perpendicular directions to form such fabric patterns as plain or hardness satin. The mechanical properties are provided in the two perpendicular directions. Fabrics are used in a laying up process to carry loads in appropriate directions. They are available on the market in dry sheet form, for wet layup process (hand impregnation) or in prepreg form. Main used woven fabrics: Fabrics can be woven in various different types of weave patterns.  Plain weave.  8 Harness satin weave.  5 Harness satin weave. PREPREGS It is protected with release foils to prevent moisture absorption, dust contamination and also to prevent solvent evaporation to maintain a minimum tack level for material application. Because resin base and hardener are already mixed together, prepregs have a limited shelf life and shop life. Therefore they are stored and shipped in a cold condition to limit the ageing effect.
  11. 11. Two distinct types of prepreg are available on the market where the reinforcement is coated with a hot melt or a solvent system, to produce a specific final product with calibrated resin content. Examples for Fiber 1. Fiberglass Fiberglass is often used for secondary structure on aircraft, such as fairings, radomes, and wing tips. Fiberglass is also used for helicopter rotor blades. There are several types of fiberglass used in the aviation industry. Electrical glass, or E-glass, is identified as such for electrical applications. It has high resistance to current flow. E-glass is made from borosilicate glass. S-glass and S2-glass identify structural fiberglass that have a higher strength than E-glass. S-glass is produced from magnesia- alumina-silicate. Advantages of fiberglass are lower cost than other composite materials, chemical or galvanic corrosion resistance, and electrical properties (fiberglass does not conduct electricity). Fiberglass has a white color and is available as a dry fiber fabric or prepreg material. 2. Kevlar
  12. 12. Kevlar is DuPont’s name for aramid fibers. Aramid fibers are light weight, strong, and tough. Two types of Aramid fiber are used in the aviation industry. Kevlar 49 has a high stiffness and Kevlar® 29 has a low stiffness. An advantage of aramid fibers is their high resistance to impact damage, so they are often used in areas prone to impact damage. The main disadvantage of aramid fibers is their general weakness in compression and hygroscopy. Service reports have indicated that some parts made from Kevlar® absorb up to 8 percent of their weight in water. Therefore, parts made from aramid fibers need to be protected from the environment. Another disadvantage is that Kevlar® is difficult to drill and cut. The fibers fuzz easily and special scissors are needed to cut the material. Kevlar is often used for military ballistic and body armor applications. It has a natural yellow color and is available as dry fabric and prepreg material. Bundles of aramid fibers are not sized by the number of fibers like carbon or fiberglass but by the weight. 3. Carbon/Graphite One of the first distinctions to be made among fibers is the difference between carbon and graphite fibers, although the terms are frequently used interchangeably. Carbon and graphite fibers are based on graphene (hexagonal) layer networks present in carbon. If the graphene layers, or planes, are stacked with three dimensional order, the material is defined as graphite. Usually extended time and temperature processing is required to form this order, making graphite fibers more expensive. Bonding between planes is weak. Disorder frequently occurs such that only two- dimensional ordering within the layers is present. This material is defined as carbon. Carbon fibers are very stiff and strong, 3 to 10 times stiffer than glass fibers. Carbon fiber is used for structural aircraft applications, such as floor beams, stabilizers, flight controls, and primary fuselage and wing structure. Advantages include its high strength and corrosion resistance. Disadvantages include lower conductivity than aluminum; therefore, a lightning protection mesh or coating is necessary for aircraft parts that are prone to lightning strikes. Another disadvantage of carbon fiber is its high cost. Carbon fiber is gray or black in color and is available as dry fabric and prepreg material. Carbon fibers have a high potential for causing galvanic corrosion when used with metallic fasteners and structures.
  13. 13. 4. Boron Boron fibers are very stiff and have a high tensile and compressive strength. The fibers have a relatively large diameter and do not flex well; therefore, they are available only as a prepreg tape product. An epoxy matrix is often used with the boron fiber. Boron fibers are used to repair cracked aluminum aircraft skins, because the thermal expansion of boron is close to aluminum and there is no galvanic corrosion potential. The boron fiber is difficult to use if the parent material surface has a contoured shape. The boron fibers are very expensive and can be hazardous for personnel. Boron fibers are used primarily in military aviation applications. 5. Ceramic Fibers Ceramic fibers are used for high-temperature applications, such as turbine blades in a gas turbine engine. The ceramic fibers can be used to temperatures up to 2,200 °F. 6. Lightning Protection Fibers An aluminum airplane is quite conductive and is able to dissipate the high currents resulting from a lightning strike. Carbon fibers are 1,000 times more resistive than aluminum to current flow, and epoxy resin is 1,000,000 times more resistive (i.e., perpendicular to the skin). The surface of an external composite component often consists of a ply or layer of conductive material for lightning strike protection because composite materials are less conductive than aluminum. Many different types of conductive materials are used ranging from nickel-coated graphite cloth to metal meshes to aluminized fiberglass to conductive paints. The materials are available for wet layup and as prepreg. In addition to a normal structural repair, the technician must also recreate the electrical conductivity designed into the part. These types of repair generally require a conductivity test to be performed with an ohmmeter to verify minimum electrical resistance across the structure. When repairing these types of structures, it is extremely important to use only the approved materials from authorized vendors, including such items as potting compounds, sealants, adhesives, and so forth.
  14. 14. COMPOSITE STRUCTURE TYPES 1. SANDWICH DESIGN Basically, the sandwich design consists of two approximately parallel thin skins with a thick core between. The sandwich design is mainly used to provide a great strength in bending. Core materials can be wood, Aramid/Phenolic or Glass/Phenolic honeycomb, metal honeycomb or foam materials. On Airbus products mainly Aramid/Phenolic, Glass/Phenolic, or metal honeycombs are used. Two main processes are used to manufacture sandwich parts: Multiphase Process: The two skins are laid-up and cured in a first step. Then the final sandwich part is manufactured in a second step, using adhesive to bond the skins to the core. Co-curing Process: The skins are cured in a single operation together with the core. 1. MONOLITHIC DESIGN Basically the monolithic design consists of a composite material made of a continuous lamination of tapes or fabrics without any core material. The construction of these elements can be made by: One-Shot Bonding Technique: Different elements like skins, stringers or stiffeners are cured in one shot. To get self-stiffened panels the modular technique is used (for example fin box). Multi-Phase Process: Different elements are cured and bonded in several steps.
  15. 15. DAMAGES AND DEFECTS IN COMPOSITE MATERIALS DELAMINATION: A delamination is a separation between different plies. This can be caused by an impact, or when there is a resin (bonding) failure for any other reason. DEBONDING: A debonding is a separation between different materials or parts of a component. This could be, for example, in a sandwich, a separation between skin and core material or on a monolythic part the separation between skin and stringer/stiffener. A debonding can be caused by an impact. SCRATCHES A scratch is linear damage of any depth and length caused by contact with a sharp object. GAUGES A gauge is wider and might be deeper than a scratch. It is usually caused by contact with a sharp object which causes a continuous, sharp or smooth channel, like a groove, in the material LIQUID INGRESS Liquid ingress is mainly caused by damage (cracks) of the skin and/or a failure in the surface protection of the sandwich components. Liquid ingress (for example, water or skydrol) can cause further damage like debonding. ABRASION An abrasion is the wearing a way of surface material caused by contact with other surfaces. EROSION Erosion is the wearing away of the material surface during flight by wind, rain…
  16. 16. LIGHTNING STRIKE Lightning strikes can cause burn marks on composite materials. Depending on the intensity, delamination and disbondings are also possible. CHEMICAL DEGRADATION Chemicals like paint strippers might cause a degradation on composite materials. PERFORATION Visual damage mainly caused by impact. Impacts could occur during flight (bird impact, hail) or during ground handling and maintenance (for example, collision with ground equipment or dropped tools). Impacts can cause a complete perforation of a monolithic or sandwich component. On sandwich components, the component may only be partly perforated. In this case only one skin is damaged and the other remains intact. DENT Light impacts can cause dents or, on sandwich parts, a depression as visual damage. Very often the visual damage is combined with a delamination or a debonding.
  17. 17. MMC SYSTEMS-Metal Matrix Sys A metal matrix composite system is generally designated simply by the metal alloy designation of the matrix and the material type, volume fraction and form of the ceramic reinforcement. MMCs differ from other composite materials in several ways. Some of these general distinctions are as follows: 1. The matrix phase of an MMC is either a pure or alloy metal as opposed to a polymer or ceramic. 2. MMCs evidence higher ductility and toughness than ceramics or CMCs, although they have lower ductility and toughness than their respective unreinforced metal matrix alloys. 3. The role of the reinforcement in MMCs is to increase strength and modulus as is the case with PMCs. Reinforcement in CMCs is generally to provide improved damage tolerance. 4. MMCs have a temperature capability generally higher than polymers and PMCs but less than ceramics and CMCs. 5. Low to moderately reinforced MMCs are formable by processes normally associated with unreinforced metals. MATRIX MATERIALS The choice of a matrix alloy for an MMC is dictated by several considerations. Of particular importance is whether the composite is to be continuously or discontinuously reinforced. The use of continuous fibers as reinforcements may result in transfer of most of the load to the reinforcing filaments and hence composite strength will be governed primarily by the fiber strength. The primary roles of the matrix alloy, then are to provide efficient transfer of load to the fibers and to blunt cracks in the event that fiber failure occurs and so the matrix alloy for a continuously reinforced MMC may be chosen more for toughness than for strength. On this basis, lower strength, more ductile, and tougher matrix alloys may be utilized in continuously reinforced MMCs. For discontinuously reinforced MMCs, the matrix may govern composite strength. Then, the choice of matrix will be influenced by consideration of the required composite strength and higher strength matrix alloys may be required.
  18. 18. Additional considerations in the choice of the matrix include potential reinforcement/matrix reactions, either during processing or in service, that might result in degraded composite performance; thermal stresses due to thermal expansion mismatch between the reinforcements and the matrix; and the influence of matrix fatigue behavior on the cyclic response of the composite. Indeed, the behavior of MMCs under cyclic loading conditions is an area requiring special consideration. In MMCs intended for use at elevated temperatures, an additional consideration is the difference in melting temperatures between the matrix and the reinforcements. A large melting temperature difference may result in matrix creep while the reinforcements remain elastic, even at temperatures approaching the matrix melting point. However, creep in both the matrix and reinforcement must be considered when there is a small melting point difference in the composite. Many different metals have been employed in MMCs and the choice of matrix material provides the basis for further classification of these composites. Alloy systems such as aluminum, copper, iron (steels), magnesium, nickel, and titanium. REINFORCEMENT MATERIALS Reinforcements can be divided into two major groups: (a) particulates or whiskers; and (b) fibers. Fiber reinforcements can be further divided into continuous and discontinuous. Fibers enhance strength in the direction of their orientation. Most often reinforcement materials for MMCs are ceramics (oxides, carbides, nitrides, etc.) which are characterized by their high strength and stiffness both at ambient and elevated temperatures. Examples of common MMC reinforcements are SiC, Al2O3, TiB2, B4C, and graphite. Metallic reinforcements are used less frequently. In many MMCs, it is necessary to apply a thin coating on the reinforcements prior to their incorporation into the metal matrix. In general, coatings on the fibers offer the following advantages: 1. Protection of fiber from reaction and diffusion with the matrix by serving as a diffusion barrier 2. Prevention of direct fiber-fiber contact
  19. 19. 3. Promotion of wetting and bonding between the fiber and the matrix 4. Relief of thermal stresses or strain concentrations between the fiber and the matrix 5. Protection of fiber during handling In some instances particulates are coated to enhance composite processing by enhancing wetting and reducing interfacial reactions. MANUFACTURING PROCESSES Choice of the primary manufacturing process for the fabrication of any MMC is dictated by many factors, the most important of which are: 1. Preservation of reinforcement strength 2. Minimization of reinforcement damage 3. Promotion of wetting and bonding between the matrix and reinforcement 4. Flexibility that allows proper backing, spacing and orientation of the reinforcements within the matrix These primary industrial manufacturing processes can be classified into liquid phase and solid state processes. Liquid phase processing is characterized by intimate interfacial contact and hence strong bonding, but can lead to the formation of a brittle interfacial layer. Solid state processes include powder blending followed by consolidation, diffusion bonding and vapor deposition. Liquid phase processes include squeeze casting and squeeze infiltration, spray deposition, slurry casting (compocasting), and reactive processing (insitu composites). Joining Methods MMC joining is not yet a mature technology and many important details are still being developed. Therefore, the applicability of a specific MMC joining method depends on the types of MMC materials being joined. They are classified to: 1. Solid State Processes Inertia Friction Welding Friction Stir Welding Ultrasonic Welding
  20. 20. Diffusion Bonding 2. Fusion Processes Laser Beam Welding Electron Beam Welding Gas Metal Arc Welding Gas Tungsten Arc Welding Resistance Spot Welding Capacitor Discharge Welding 3. Other Processes Brazing Soldering Adhesive Bonding Mechanical Fastening Cast-insert Joining Transient Liquid Phase Rapid Infrared Joining
  21. 21. BIO-COMPOSITE MATERIALS After decades of high-tech developments of artificial fibers like aramid, carbon and glass it is remarkable that natural fibers have gained a renewed interest, especially as a glass fiber substitute in automotive industries. New environmental regulations and societal concern have triggered the search for new products and processes that are compatible to the environment. The incorporation of bio-resources in to composite materials can reduce further dependency of petroleum reserves. The major limitations of present biopolymers are their high cost. Again renewable resource based bio-plastics are currently being developed and need to be researched more to overcome the performance limitations. Bio-composites can supplement and eventually replace petroleum based composite materials in several applications thus offering new agricultural, environmental, manufacturing and consumer benefits. The main advantage of using renewable materials is that the global CO2 balance is kept at a stable level. Classification of Bio-composites
  22. 22. Classification of Bio-fibers Matrix Polymers Among all the matrix polymers; polypropylene (PP) has attained much commercial success in bio-composites for automotive applications. Although unsaturated polyester resin can be used in bio-composite applications commercially, the non-recyclable nature of this thermoset resin over thermoplastic recyclable PP is hindering its growing importance.
  23. 23. SMART COMPOSITE MATERIALS Smart material systems often consist of mixtures of several different passive and active materials. Mixing the constituent materials in the right way makes it possible to make new smart composites with properties beyond those of the individual constituents. Intrinsically smart structural composites are multifunctional structural materials which can perform functions such as sensing strain, stress, damage or temperature; thermoelectric energy generation; EMI shielding; electric current rectification; and vibration reduction. These capabilities are rendered by the use of materials science concepts to enhance functionality without compromising structural properties. They are not achieved by the embedding of devices in the structure. Intrinsically smart structural composites have been attained in cement-matrix composites containing short electrically conducting fibers and in polymer-matrix composites with continuous carbon fibers. Cement-matrix composites are important for infrastructure, while polymer-matrix composites are useful for lightweight structures. Smart structures have the ability to sense certain stimuli and respond in an appropriate fashion, somewhat like a human being. Sensing is the most fundamental aspect of a smart structure. A structural composite which is itself a sensor is said to be self-sensing. It is multifunctional. There are: cement-matrix and polymer-matrix composites Cement-matrix composites Cement-matrix composites include concrete (containing coarse and fine aggregates), mortar (containing fine but no coarse aggregate), and cement paste (containing no aggregate, neither coarse nor fine). Other fillers, called admixtures, can be added to the mix to improve the properties of the composite. Admixtures are discontinuous, so that they can be included in the mix. They can be particles, such as silica fume (a fine particulate) or latex (a polymer in the form of a dispersion). Short fibers, such as polymer, steel glass or carbon fibers, and liquids, such as methylcellulose aqueous solution, water reducing agents or defoamers, can be used.
  24. 24. Polymer-matrix composites Polymer-matrix composites for structural applications typically contain continuous carbon, polymer, or glass fibers, as continuous fibers tend to be more effective than short fibers as reinforcement. Polymer-matrix composites with continuous carbon fibers are used for aerospace, automobile and civil structures. (In contrast, continuous fibers are too expensive for reinforcing concrete.) The fact that carbon fibers are electrically conducting, whereas polymer and glass fibers are not, means that carbon fiber composites are predominant among polymer-matrix composites that are intrinsically smart.
  25. 25. Preferences   The materials of BASIC course from EGYPT AIR Company.  aft/amt_airframe_handbook/media/ama_Ch07.pdf  BANG/Composite%20Materials/Learning%20material%20- %20composite%20material.pdf  web&cd=1&cad=rja&uact=8&ved=0CC4QFjAA&url=http%3A% composite_materials_as_alternatives_to_petroleum- based_composites_for_automotive_applications%2Ffile%2F60b7d 51b62c2e6a18a.pdf&ei=84IxU7enLsSdtQag7oGgCQ&usg=AFQj CNESXZiNeQ5IuckX51pN1AcMH75mZw&sig2=x7nJzziv9G8x CF0wpIw4bw  4A.pdf  sically%20smart%20structural%20composites.pdf  tera.pdf 