DEVELOPMENT AND ANALYSIS OF AUTOMOTIVE GEAR USING ALUMINIUM MATRIX COMPOSITES

CHAPTER-1INTRODUCTION

INTRODUCTION1.1- INTRODUCTION TO LIGHT WEIGHT AUTOMOBILE:Material competition in the automotive market has been traditionally intensive. Steel has been the dominant material used in building automobiles since the 1920s. What types of materials are likely to be winners in the 21st century?The automotive manufacturers decisions on materials usage are complex and are determined by a number of factors. The increasing requirement to improve fuel economy triggered by concerns about global warming and energy usage has a significant influence on the choice of materials. For- ExampleThe US government regulations mandate that the automotive companies. a)-Reduce vehicle exhaust emissions.b)-Improve occupant safety.c)-Reduce fuel consumptions.To meet this requirement, automotive manufacturers are making efforts to improve conventional engine efficiency, to develop new power trains such as hybrid systems and to reduce vehicle weight.Weight reduction is particularly important because average vehicle weight is expected to increase since the automobile industry will continue to market new models with increased luxury, convenience, performance, and safety as demanded by their customers. Safety features such as anti-block systems, air bags, and increasing safety body structure contribute to vehicle weight gain. Although, the car companies have responded to this by improving design and power train efficiency, these incremental improvements have not yet enabled a significant reduction in overall weight. If this is to be achieved, there will have to be a radical increase in the use of light weight materials. A rule of thumb is that 10% weight reduction approximately equals a 5.5% improvement in fuel economy. An important fact is that weight reduction has a ripple effect on fuel efficiency.For example- weight reduction enables the manufacture to develop the same vehicle performance with a smaller engine, and such a smaller engine enables the use of a smaller transmission and a smaller fuel tank. With this ripple effect, it is estimated that 10% of vehicle weight reduction results in 810% of fuel economy improvement.In conclusion, automotive materials can have an important impact on the environment. In a vehicle, every pound of aluminum that replaces two pounds of steel can save 20 pounds of CO2 from being emitted. The use of lightweight materials can help reduce vehicle weight and improve fuel economy. The pressure for weight reduction has driven a gradual decrease in the amount of steel and cast iron used in vehicles and the corresponding increase in the amount of alternative materials, especially aluminium and plastics.VEHICLE WEIGHT TRENDSAs size increases and more safety, performance and luxury features are added to vehicles, they continue to increase in weight. Since 1990, the weight of a typical family vehicle has steadily risen from 3140.5 pounds to 3357.5 pounds. A specific example of the increasing weight trend is the VW GTI. The original version of the GTI, introduced in 1976, weighed 1804 pounds, while the latest version weighs 2939 pounds. This increase represents a weight gain of approximately 40% over the 18-year life of the GTI. The original VW Golf is a substantially larger vehicle than the current Smart sub-compact, yet the Smart weighs slightly more than the Golf. Simultaneous to the weight increase trend, there has also been an increase use of aluminum castings, which has partially offset further weight increases. The typical family vehicle (i.e. cars, minivans, SUVs and light trucks) has increased in its aluminum casting content from 92.3 pounds in 1978 to 240 pounds in 2002.

FUEL REDUCTION POTENTIAL ON REDUCED WEIGHTA vehicle that uses less fuel produces fewer greenhouse gas emissions. Over the average lifetime of a vehicle, every pound of aluminum that replaces two pounds of steel can save 20 pounds of CO2 from being emitted. Using aluminum to cut a vehicle's weight by 10% can boost its fuel economy up to 8%, or as much as 2.5 extra miles per gallon. BMW studied vehicle weight reduction through the use of aluminum and reported fuel savings of between five and ten percent for each 10 percent reduction in weight. The Argonne National Laboratory also studied vehicle light weighting and reported a fuel savings of 6.6 percent for every 10 percent reduction in weight.TP 4PT A 6 to 8% fuel savings can be realized for every 10% reduction in weight from substituting aluminum for steel. Aluminum absorbs nearly twice as much energy as steel, and during a crash, aluminum folds like an accordion, letting the vehicle - not its passengers - absorb more of the crash forces. Lighter vehicles generally accelerate quicker and require shorter stopping distances than heavier vehicles. Aluminum castings have been critical to automakers meeting or exceeding federally mandated CAF standards. It is estimated that lightweight castings have increased the CAF fuel efficiency by 5% over the last ten years.

1.2- BACKGROUND:

1.2.1- ALUMINUM:According to Jefferson Lab, "Scientists suspected than an unknown metal existed in alum as early as 1787, but they did not have a way to extract it until 1825. Hans Christian Oersted, a Danish chemist, was the first to produce tiny amounts of aluminum. Two years later, Friedrich Wohler, a German chemist, developed a different way to obtain the metal. By 1845, he was able to produce samples large enough to determine some of aluminum's basic properties. Wohlers method was improved in 1854 by Henri Etienne Sainte-Claire Deville, a French chemist. Deville's process allowed for the commercial production of aluminum. As a result, the price of the metal dropped from around $1200 per kilogram in 1852 to around $40 per kilogram in 1859. Unfortunately, the metal remained too expensive to be widely used.Aluminium(oraluminum) is achemical elementin theboron groupwith symbolAland atomic13. It is a silvery white, soft, ductile metal. Aluminium isthe third most abundant element(afteroxygenandsilicon), and themost abundant metal, in theEarths crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extremereducing environments. Instead, it is found combined in over 270 differentminerals. The chiefore of aluminium isbauxite.Aluminium is remarkable for the metal's lowdensityand for its ability to resistcorrosion due to the phenomenon ofpassivation. Structural components made from aluminium and itsalloysare vital to theaerospaceindustry and are important in other areas of transportationand structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.PHYSICALAluminium is a relatively soft, durable, lightweight,ductileandmalleablemetalwith appearance ranging from silvery to dull gray, depending on the surface roughness. It is nonmagnetic and does not easily ignite. Theyield strengthof pure aluminium is 711MPa, whilealuminium alloyshave yield strengths ranging from 200 MPa to 600 MPa. Aluminium has one third in density and stiffness of steel. It is easilymachined, cast,drawnandextruded. Aluminium is a goodthermalandelectrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of being asuperconductor, with a superconducting critical temperature of 1.2Kelvinand a critical magnetic field of about 100gauss(10milliteslas). CHEMICALCorrosionresistance can be excellent due to a thin surface layer ofaluminium oxidethat forms when the metal is exposed to air, effectively preventing furtheroxidation. The strongest aluminium alloys are less corrosion resistant due togalvanicreactions with alloyedcopper. This corrosion resistance is also often greatly reduced by aqueous salts, particularly in the presence of dissimilar metals. Owing to its resistance to corrosion, aluminium is one of the few metals that retain silvery reflectance in finely powdered form, making it an important component ofsilver-coloredpaints. Aluminium mirror finish has the highestreflectanceof any metal in the 200400nm (UV) and the 3,00010,000nm (farIR) regions; in the 400700nm visible range it is slightly outperformed bytinandsilverand in the 7003000 (near IR) by silver, gold and copper.RECYCLINGAluminium is theoretically 100% recyclable without any loss of its natural qualities. According to the InternationalMetal Stocks in Society report, the globalper capitastock of aluminium in use in society (i.e. in cars, buildings, electronics etc.) is 80kg. Much of this is in more-developed countries (350500kg per capita) rather than less-developed countries (35kg per capita). InEuropealuminium experiences high rates of recycling, ranging from 42% of beverage cans, 85% of construction materials and 95% of transport vehicles.Recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium. Secondary aluminium is produced in a wide range of formats and is employed in 80% of alloy injections.

1.2.2-ALUMINUM ALLOY:Aluminium alloysarealloysin whichaluminium(Al) is the predominant metal. The typical alloying elements arecopper,magnesium,manganese,siliconandzinc. There are two principal classifications, namelycastingalloys and wrought alloys, both of which are further subdivided into the categoriesheat-treatableand non-heat-treatable. Alloys composed mostly of the two lightweight metals aluminium and magnesium have been very important inaerospace manufacturingsince somewhat before 1940. Aluminium-magnesium alloys are both lighter than other aluminium alloys and much less flammable than alloys that contain a very high percentage of Selecting the right alloy for a given application entails considerations of itstensile strength,density,ductility, formability, workability,weld ability, andcorrosion resistance.Aluminium alloys typically have anelastic modulusof about 70GPa, which is about one-third of the elastic modulus of most kinds ofsteelandsteel alloys. Therefore, for a given load, a component or unit made of an aluminium alloy will experience a greater elastic deformation than a steel part of the identical size and shape. Though there are aluminium alloys with somewhat-higher tensile strengths than the commonly used kinds of steel, simply replacing a steel part with an aluminium alloy might lead to problems.Aluminium alloys are widely used in automotive engines, particularly incylinder blocksandcrankcasesdue to the weight savings that are possible. Since aluminium alloys are susceptible to warping at elevated temperatures, the cooling system of such engines is critical. WROUGHT ALLOYSThe International Alloy Designation System is the most widely accepted naming scheme forwrought alloys. Each alloy is given a four-digit number, where the first digit indicates the major alloying elements. 1000 series are essentiallypure aluminiumwith a minimum 99% aluminium content by weight and can bework hardened. 2000 series are alloyed withcopper, can beprecipitation hardenedto strengths comparable tosteel. Formerly referred to asduralumin, they were once the most common aerospace alloys, but were susceptible tostress corrosion crackingand are increasingly replaced by 7000 series in new designs. 3000 series are alloyed withmanganese, and can bework hardened. 4000 series are alloyed withsilicon. They are also known assliming. 5000 series are alloyed withmagnesium. 6000 series are alloyed withmagnesiumandsilicon, are easy to machine, and can be precipitation hardened, but not to the high strengths that 2000 and 7000 can reach. 7000 series are alloyed withzinc, and can be precipitation hardened to the highest strengths of any aluminium alloy. 8000 series is a category mainly used forlithiumalloysUSES: 5000 series

Aluminium alloy 5005 is used in decorative and architectural applications that require an anodized finish. Aluminium alloys 5052, 5251, and 5754 are very similar grades, only differing in the amount of magnesium. 5052 has 2.5% magnesium and is commonly used in the U.S.; 5251 has 2% magnesium and is commonly used in the UK; and 5754 has 3% magnesium and is commonly used in Europe. Due to their formability, corrosion resistance and weld ability these grades are commonly used in pressure vessels, tanks, fitting, boat hulls, and van bodies. Their salt water corrosion resistance is better than the 1200 grade and their strength is better than the 3003 grade. Aluminium alloy 5083is an aluminium alloy suitable forcryogenicapplications down to design temperatures of165 C(265F), since alloys of this type do not show thetransition phenomenon. This alloy is also common for the marine applications such as body materials for ships, underwater vehicles etc.

6000 series

6061-T6 is one of the most commonly used 6000 series aluminum alloys (see6061 aluminium alloy) 6063is an aluminium alloy, with magnesium and silicon as the alloying elements. The standard controlling its composition is maintained by The Aluminum Association. It has generally good mechanical properties and is heat treatable and wieldable. It is similar to the British aluminium alloy HE9. 6063 is mostly used in extruded shapes for architecture, particularly window frames, door frames, roofs, and sign frames. It is typically produced with very smooth surfaces fit for anodizing.1.2.3- SILICON CARBIDE:Non-systematic, less-recognized, and often unverified syntheses of silicon carbide were reported early, J. J. Berzelius's reduction of potassium fluorosilicate by potassium (1810); Charles Mansute Deserets (17921863) passing an electric current through a carbon rod embedded in sand (1849); Robert Sydney Marsden's (18561919) dissolution of silica in molten silver in a graphite crucible (1881); Albert Colson's heating of silicon under a stream of ethylene (1882); and Paul Schuetzenberger's heating of a mixture of silicon and silica in a graphite crucible (1881).Nevertheless, wide-scale production is credited to Edward Goodrich Acheson in 1890. Acheson was attempting to prepare artificial diamonds when he heated a mixture of clay (aluminum silicate) and powdered coke (carbon) in an iron bowl. He called the blue crystals that Formed Carborundum, believing it to be a new compound of carbon and aluminum, similar to corundum. In 1893, Henri Moissan discovered the very rare naturally-occurring SiC mineral while examining rock samples found in the Canyon Diablo meteorite in Arizona. The mineral was named moissanite in his honor. Moissan also synthesized SiC by several routes, including: the dissolution of carbon in molten silicon; melting a mixture of calcium carbide and silica; and by reducing silica with carbon in an electric furnace. However, Moissan ascribed the original discovery of SiC to Acheson in 1903. Because of the rarity of natural moissanite, most silicon carbide is synthetic. It is used as an abrasive, and more recently as a semiconductor and diamond stimulant of gem quality. The simplest manufacturing process is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1600 and 2500 C. Fine SiO2 particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material. The silica fume, which is a byproduct of producing silicon metal and ferrosilicon alloys, also can be converted to SiC by heating with graphite.TABLE 1.1 SILICON CARBIDE PROPERTIES

MechanicalSI/Metric (Imperial) SI/Metric (Imperial)

Densitygm/cc (lb/ft3) 3.1 (193.5)

Porosity% (%) 0 (0)

Color black

Flexural Strength MPa (lb/in2x103) 550 (80)

Elastic ModulusGPa (lb/in2x106) 410 (59.5)

Shear ModulusGPa (lb/in2x106)

Bulk ModulusGPa (lb/in2x106)

Poissons Ratio 0.14 (0.14)

Compressive StrengthMPa (lb/in2x103) 3900 (566)

HardnessKg/mm2 2800

Fracture Toughness KICMPam1/2 4.6

Maximum Use Temperature (no load)C (F) 1650 (3000)

Thermal

Thermal ConductivityW/mK (BTUin/ft2hrF) 120 (830)

Coefficient of Thermal Expansion106/C (106/F) 4.0 (2.2)

Specific HeatJ/KgK (Btu/lbF) 750 (0.18)

Electrical

Dielectric Strengthac-kv/mm (volts/mil) semiconductor

1.2.4-COMPOSITES:Mankind has been aware composite materials since several hundred years before Christ and applied innovation to improve the quality of life. Although it is not clear has to how Man understood the fact that mud bricks made sturdier houses if lined with straw, he used them to make buildings that lasted. Ancient Pharaohs made their slaves use bricks with to straw to enhance the structural integrity of their buildings, some of which testify to wisdom of the dead civilization even today. Contemporary composites results from research and innovation from past few decades have progressed from glass fiber for automobile bodies to particulate composites for aerospace and a range other applications.A composite material is a material made up of two or more materials that are combined in a way that allows the materials to stay distinct and identifiable. The purpose of composites is to allowthe new material to have strengths from both materials, often times covering the original materials' weaknesses. Composites are different from alloys because alloys are combined in such a way that it is impossible to tell one particle, element, or substance from the other. Some common composite materials include concrete, fiberglass, mud bricks, and natural composites such as rock and wood.1.2.5- CLASSIFICATION OF COMPOSITES:Composite materials are commonly classified at following two distinct levels: The first level of classification is usually made with respect to the matrix constituent.

1.2.6- POLYMER MATRIX COMPOSITES (PMCS):Polymers make ideal materials as they can be processed easily, possess lightweight, and desirable mechanical properties. It follows, therefore, that high temperature resins are extensively used in aeronautical applications. Two main kinds of polymers are thermo sets and thermoplastics. Thermo sets have qualities such as a well-bonded three-dimensional molecular structure after curing. They decompose instead of melting on hardening. Merely changing the basic composition of the resin is enough to alter the conditions suitably for curing and determine its other characteristics. They can be retained in a partially cured condition too over prolonged periods of time, rendering Thermo sets very flexible. Thus, they are most suited as matrix bases for advanced conditions fiber reinforced composites. Thermoplastics have one- or two-dimensional molecular structure and they tend to at an elevated temperature and show exaggerated melting point. Another advantage is that the process of softening at elevated temperatures can reversed to regain its properties during cooling, facilitating applications of conventional compress techniques to mould the compounds. Resins reinforced with thermoplastics now comprised an emerging group of composites. The theme of most experiments in this area to improve the base properties of the resins and extract the greatest functional advantages from them in new avenues, including attempts to replace metals in die-casting processes. In crystalline thermoplastics, the reinforcement affects the morphology to a considerable extent, prompting the reinforcement to empower nucleation. Whenever crystalline or amorphous, these resins possess the facility to alter their creep over an extensive range of temperature. But this range includes the point at which the usage of resins is constrained, and the reinforcement in such systems can increase the failure load as well as creep resistance.

Thermoplastics

PolypropyleneNylonsPolyamidesPolystyrenePolyethylene

Fig 1.1 kinds of thermoplastics

1.2.7-METAL MATRIX COMPOSITES (MMCS):Metal matrix composites, at present though generating a wide interest in research fraternity, are not as widely in use as their plastic counterparts. High strength, fracture toughness and stiffness are offered by metal matrices than those offered by their polymer counterparts. They can withstand elevated temperature in corrosive environment than polymer composites. Most metals and alloys could be used as matrices and they require reinforcement materials which need to be stable over a range of temperature and non-reactive too. However the guiding aspect for the choice depends essentially on the matrix material. Light metals form the matrix for temperature application and the reinforcements in addition to the aforementioned reasons are characterized by high moduli. Most metals and alloys make good matrices. However, practically, the choices for low temperature applications are not many. Only light metals are responsive, with their low density proving an advantage. Titanium, Aluminium and magnesium are the popular matrix metals currently in vogue, which are particularly useful for aircraft applications. If metallic matrix materials have to offer high strength, they require high modulus reinforcements. The strength-to-weight ratios of resulting composites can be higher than most alloys. The melting point, physical and mechanical properties of the composite at various temperatures determine the service temperature of composites. Most metals, ceramics and compounds can be used with matrices of low melting point alloys. The choice of reinforcements becomes more stunted with increase in the melting temperature of matrix materials.

ADVANTAGES OF MMCS Higher strength-to-density ratios. Higher stiffness-to-density ratios. Better fatigue resistance. Better elevated temperature properties.

THE ADVANTAGES OF MMCS OVER POLYMER MATRIX COMPOSITES ARE: Higher temperature capability. Fire resistance. Higher transverse stiffness and strength. No moisture absorption. Higher electrical and thermal conductivities. Better radiation resistance.DISADVANTAGES OF MMCS:Some of the disadvantages of MMCs compared to polymer matrix composites are: Higher cost of some material systems Relatively immature technology Complex fabrication methods for fiber-reinforced systems (except for casting) Limited service experience.

1.2.8-CERAMIC MATRIX COMPOSITES (CMCS):Ceramics can be described as solid materials which exhibit very strong ionic bonding in general and in few cases covalent bonding. High melting points, good corrosion resistance, stability at elevated temperatures and high compressive strength, render ceramic-based matrix materials a favorite for applications requiring a structural material that doesnt give way at temperatures above 1500C. Naturally, ceramic matrices are the obvious choice for high temperature applications. High modulus of elasticity and low tensile strain, which most ceramics posses, have combined to cause the failure of attempts to add reinforcements to obtain strength improvement. A material is reinforcement to utilize the higher tensile strength of the fiber, to produce an increase in load bearing capacity of the matrix. Addition of high-strength fiber to a weaker ceramic has not always been successful and often the resultant composite has proved to be weaker. When ceramics have a higher thermal expansion coefficient than reinforcement materials, the resultant composite is unlikely to have a superior level of strength. In that case, the composite will develop strength within ceramic at the time of cooling resulting in micro cracks extending from fiber to fiber within the matrix. Micro cracking can result in a composite with tensile strength lower than that of the matrix.

1.2.9 - CARBON MATRIX COMPOSITES (CMCS):Carbon and graphite have a special place in composite materials options, both being highly superior, high temperature materials with strengths and rigidity that are not affected by temperature up to 2300C. This carbon-carbon composite is fabricated through compaction of carbon or multiple impregnations of porous frames with liquid carbonized precursors and subsequent pyrolization. They can also be manufactured through chemical vapour deposition of paralytic carbon. However, their capacity to retain their properties at room temperature as well as at temperature in the range of 2400C and their dimensional stability make them the oblivious choice in a garnet of applications related to aeronautics, military, industry and space. Components, that are exposed to higher temperature and on which the demands for high standard performance are many, are most likely to have carbon-carbon composites used in them.

1.2.10- GLASS MATRIX COMPOSITES (GMCS):In comparison to ceramics and even considered on their own merit, glass matrices are found to be more reinforcement-friendly. The various manufacturing methods of polymers can be used for glass matrices. Glasses are meant to improve upon performance of several applications. Glass matrix composite with high strength and modulus can be obtained and they can be maintained up to temperature of the order of 650C. Composites with glass matrices are considered superior in dimensions to polymer or metal system, due to the low thermal expansion behavior. This property allows fabrication of many components in intricate shapes and their tribological characters are considered very special. Since the elastic modulus of glass is far lower than of any prospective reinforcement materials, application of stress usually results in high elasticity modulus fiber that the tensile strength of the composite its considerably enhanced than that of the constituents, which is not case in ceramic matrices The second level of classification refers to the reinforcement form:

1.2.11-REINFORCEMENTS:Reinforcements for the composites can be fibers, fabrics particles or whiskers. Fibers are essentially characterized by one very long axis with other two axes either often circular or near circular. Particles have no preferred orientation and so does their shape. Whiskers have a preferred shape but are small both in diameter and length as compared to fibers. Figure 1.4 shows types of reinforcements in composites. Reinforcing constituents in composites, as the word indicates, provide the strength that makes the composite what it is. But they also serve certain additional purposes of heat resistance or conduction, resistance to corrosion and provide rigidity. Reinforcement can be made to perform all or one of these functions as per the requirements. A reinforcement that embellishes the matrix strength must be stronger and stiffer than the matrix and capable of changing failure mechanism to the advantage of the composite. This means that the ductility should be minimum or even nil the composite must behave as brittle as possible.1.2.12-FIBRE REINFORCED COMPOSITES:Fibers are the important class of reinforcements, as they satisfy the desired conditions and transfer strength to the matrix constituent influencing and enhancing their properties as desired. Glass fibers are the earliest known fibers used to reinforce materials. Ceramic and metal fibers were subsequently found out and put to extensive use, to render composites Stiffer more resistant to heat. Fibers fall short of ideal performance due to several factors. The performance of a fiber composite is judged by its length, shape, and orientation, composition of the fibers and the mechanical properties of the matrix. In very strong matrices, moduli and strengths have not been observed. Application of the strength of the composites with such matrices and several orientations is also possible. Given the fact that the vast difference in length and effective dia.

Reinforcements

Directionally Soeutectics lidifiedParticulatesFlakeWhiskersFilledFibers

MicrosporesParticle filled

HollowSolid

Fig-1.2 types of reinforcementsof the fiber are assets to a fiber composite, it follows that greater strength in the fiber can be achieved by smaller diameters due to minimization or total elimination of surface of surface defects. After flat-thin filaments came into vogue, fibers rectangular cross sections have provided new options for applications in high strength structures. Owing to their shapes, these fibers provide perfect packing, while hollow fibers show better structural efficiency in composites that are desired for their stiffness and compressive strengths. In hollow fibers, the transverse compressive strength is lower than that of a solid fiber composite whenever the hollow portion is more than half the total fiber diameter. However, they are not easy to handle and fabricate.1.2.13-TYPES OF FIBERS:Organic and inorganic fibers are used to reinforce composite materials. Almost all organic fibers have low density, flexibility, and elasticity. Inorganic fibers are of high modulus, high thermal stability and possess greater rigidity than organic fibers and notwithstanding the diverse advantages of organic fibers which render the composites in which they are used. Mainly, the following different types of fibers namely, glass fibers, silicon carbide fibers, high silica and quartz fibers, alumina fibers, metal fibers and wires, graphite fibers, boron fibers, aramid fibers and multiphase fibers are used. Among the glass fibers, it is again classified into E-glass, A-glass, R-glass etc. There is a greater marker and higher degree of commercial movement of organic fibers. The potential of fibers of graphite, silica carbide and boron are also exercising the scientific mind due to their applications in advanced composites.I. GLASS FIBERS: Over 95% of the fibers used in reinforced plastics are glass fibers, as they are inexpensive, easy to manufacture and possess high strength and stiffness with respect to the plastics with which they are reinforced. Their low density, resistance to chemicals, insulation capacity are other bonus characteristics, although the one major disadvantage in glass is that it is prone to break when subjected to high tensile stress for a long time. This property mitigates the effective strength of glass especially when glass is expected to sustain loads for many months or years continuously. Addition of chemicals to silica sand while making glass yields different types of glasses.

II. METALS FIBERS: As reinforcement, metal fibers have many advantages. They are easily produced using several fabrication processes and are more ductile, apart from being not too sensitive to surface damage and possess high strengths and temperature resistance. However, their weight and the tendency to react each other through alloying mechanisms are major disadvantages. Metal wires, of the continuous version; also reinforce plastics like polyethylene and epoxy temperature and the resultant steep variations of thermal expansion coefficient with the resins are a discouragement that limits their application.III. ALUMINA FIBERS: Alumina aluminium oxide fibers, basically developed for use in metal matrices are considered a potential resin-matrix composite reinforcement. It offers good compressive strength rather than tensile strength. Its important property is its high melting point of about 2000C and the composite can be successfully used at temperature up to about 1000C. Magnesium and aluminum matrices frequently use alumina fiber reinforced composites as they do not damage the fiber even in the liquid state.

IV. BORON FIBERS: They are basically composites, in which boron is coated on a substance which forms the substrate, usually made of tungsten. Boron-tungsten fibers are obtained by allowing hot tungsten filament through a mixture of gases. The tungsten however remains constant in its thickness. Properties of boron fibers generally change with the diameter, because of the changing ratio of boron to tungsten and the surface defects that change according to size. Boron coated carbons are much cheaper to make than boron tungsten fiber. But is low modulus of elasticity often works against it.

V. SILICON CARBIDE FIBERS:Silicon carbide can be coated over a few metals and their room temperature tensile strengths and tensile moduli are like those boron-tungsten. The advantages of silicon carbide-tungsten are several and are more desirable than uncoated boron tungsten fibers. However, Silicon carbide-tungsten fibers are dense compared to boron-tungsten fibers of the same diameters. They are prone to surface damage and need careful, delicate handling, especially during fabrication of the composite. Further, above 930C weakening reactions occur between tungsten and silicon carbide, making it different to maintain balance in high-temperature matrix formations. Silicon carbide on carbon substrates have several advantages, viz. no reaction at high temperature, being lighter than silicon carbide tungsten and possessing tensile strengths and modulus that is are often better than those of silicon carbide-tungsten and boron fibers.

VI. QUARTZ AND SILICA FIBERS:The glass-types typically contain about 50 to 70% silica. Quartz is even more pure, and quartz fibers are made from natural quartz crystals that contain 99.9% silica, possessing nearly all the properties of pure solid quartz. They are highly elastic and can be stretched to 1% of their length before break point. Both silica and quartz are not affected by acid attacks and are resistant to moisture. Owing to their thermal properties, silica and quartz are the natural choice as fibers in several applications. They have good insulting properties and do not melt at temperature up to 1600C. In addition, they have a low thermal expansion coefficient which makes them withstand high temperatures.

VII. GRAPHITE FIBERS:While use of the term carbon for graphite is permissible, there is one basic difference between the two. Element analysis of poly-acryl-nitride (PAN) base carbon fibers show that they consist of 91 to 94% carbon. But graphite fibers are over 99% carbon. The difference arises from the fact that the fibers are made at different temperatures PAN-based carbon cloth or fiber is produced at about 1320C, while graphite fibers and cloth are graphitized at 1950 to 3000C. Cheaper pitch base fiber are now being developed, with greater performance potential and there are possibilities of the increased use of graphite fibers.

VIII. MULTIPHASE FIBERS: Spool able filaments made by chemical vapors deposition processes are usually the multiphase variety and they usually comprise materials like boron, silicon and their carbides formed on surface of a very fine filament substrate like carbon or tungsten. They are usually good for high temperature applications, due to their reduced reaction with higher melting temperature of metals than graphite and other metallic fibers. Boron filaments are sought after for structural and intermediate-temperature composites. A poly-phase fiber is a core-sheath fiber consisting of a poly-crystalline core. 1.2.14-LAMINAR COMPOSITES: Laminar composites are found in as many combinations as the number of materials. They can be described as materials comprising of layers of materials bonded together. These may be of several layers of two or more metal materials occurring alternately or in a determined order more than once, and in as many numbers as required for a specific purpose. Clad and sandwich laminates have many areas as it ought to be, although they are known to follow the rule of mixtures from the modulus and strength point of view. Other intrinsic values pertaining to metal-matrix, metal-reinforced composites are also fairly well known.

1.2.15-FLAKE COMPOSITES: Flakes are often used in place of fibers as can be densely packed. Metal flakes that are in close contact with each other in polymer matrices can conduct electricity or heat, while mica flakes and glass can resist both. Flakes are not expensive to produce and usually cost less than fibers. Flakes have various advantages over fibers in structural applications. Parallel flakes filled composites provide uniform mechanical properties in the same plane as the flakes. While angle-plying is difficult in continuous fibers which need to approach isotropic properties, it is not so in flakes. Flake composites have a higher theoretical modulus of elasticity than fiber reinforced composites. They are relatively cheaper to produce and be handled in small quantities.1.2.16-FILLED COMPOSITES:Filled composites result from addition of filer materials to plastic matrices to replace a portion of the matrix, enhance or change the properties of the composites. The fillers also enhance strength and reduce weight. Another type of filled composite is the product of structure infiltrated with a second-phase filler material. The skeleton could be a group of cells, honeycomb structures, like a network of open pores. The infiltrated could also be independent of the matrix and yet bind the components like powders or fibers, or they could just be used to fill voids. Fillers produced from powders are also considered as particulate composite.

1.2.17-PARTICULATE REINFORCED COMPOSITES: Microstructures of metal and ceramics composites, which show particles of one phase strewn in the other, are known as particle reinforced composites. Square, triangular and round shapes of reinforcement are known, but the dimensions of all their sides are observed to be more or less equal. The size and volume concentration of the dispersion distinguishes it from dispersion hardened materials. In particulate composites, the particles strengthen the system by the hydrostatic coercion of fillers in matrices and by their hardness relative to the matrix. Three-dimensional reinforcement in composites offers isotropic properties, because of the three systematical orthogonal planes. Since it is not homogeneous, the material properties acquire sensitivity to the constituent properties, as well as the interfacial properties and geometric shapes of the array. The composites strength usually depends on the diameter of the particles, the inter-particle spacing, and the volume fraction of the reinforcement. The matrix properties influence the behavior of particulate composite too.

1.2.18-COMPARISON WITH METALS:Requirements governing the choice of materials apply to both metals and reinforced plastics. It is, therefore, imperative to briefly compare main characteristics of the two. Composites offer significant weight saving over existing metals. Composites can provide structures that are 25-45% lighter than the conventional aluminium structures designed to meet the same functional requirements. This is due to the lower density of the composites. Depending on material form, composite densities range from 1260 to 1820 kg/in3 (0.045 to 0.065 lb/in3) as compared to 2800 kg/in3 (0.10 lb/in3) for aluminium. Some applications may require thicker composite sections to meet strength/stiffness requirements, however, weight savings will still result. Unidirectional fiber composites have specific tensile strength (ratio of material strength to density) about 4 to 6 times greater than that of steel and aluminium. Unidirectional composites have specific -modulus (ratio of the material stiffness to density) about 3 to 5 times greater than that of steel and aluminium. Fatigue endurance limit of composites may approach 60% of their ultimate tensile strength. For steel and aluminium, this value is considerably lower. Fiber composites are more versatile than metals, and can be tailored to meet performance needs and complex design requirements such as aero-elastic loading on the wings and the vertical & the horizontal stabilizers of aircraft. Fiber reinforced composites can be designed with excellent structural damping features. As such, they are less noisy and provide lower vibration transmission than metals. High corrosion resistance of fiber composites contributes to reduce life- cycle cost. Composites offer lower manufacturing cost principally by reducing significantly the number of detailed parts and expensive technical joints required to form large metal structural components. In other words, composite parts can eliminate joints/fasteners thereby providing parts simplification and integrated design. Long term service experience of composite material environment and durability behavior is limited in comparison with metals.

1.2.19-ADVANTAGES AND DISADVANTAGE OF COMPOSITES:

ADVANTAGESThe advantages exhibited by composite materials, which are of significant use in aerospace and automobile industry are as follows: High resistance to fatigue and corrosion degradation. High strength or stiffness to weight ratio. As enumerated above, weight savings are significant ranging from 25-45% of the weight of conventional metallic designs. Due to greater reliability, there are fewer inspections and structural repairs. Directional tailoring capabilities to meet the design requirements. The fiber pattern can be laid in a manner that will tailor the structure to efficiently sustain the applied loads. Fiber to fiber redundant load path. Improved dent resistance is normally achieved. Composite panels do not sustain damage as easily as thin gage sheet metals. It is easier to achieve smooth aerodynamic profiles for drag reduction. Complex double-curvature parts with a smooth surface finish can be made in one manufacturing operation. Composites offer improved torsion stiffness. This implies high whirling speeds, reduced number of intermediate bearings and supporting structural elements. The overall part count and manufacturing & assembly costs are thus reduced. High resistance to impact damage. Thermoplastics have rapid process cycles, making them attractive for high volume commercial applications that traditionally have been the domain of sheet metals. Moreover, thermoplastics can also be reformed. Like metals, thermoplastics have indefinite shelf life. Composites are dimensionally stable i.e. they have low thermal conductivity and low coefficient of thermal expansion. Composite materials can be tailored to comply with a broad range of thermal expansion design requirements and to minimize thermal stresses. Manufacture and assembly are simplified because of part integration (joint/fastener reduction) thereby reducing cost. The improved weather ability of composites in a marine environment as well as their corrosion resistance and durability reduce the down time for maintenance. Close tolerances can be achieved without machining. Material is reduced because composite parts and structures are frequently built to shape rather than machined to the required configuration, as is common with metals. Excellent heat sink properties of composites, especially Carbon-Carbon, combined with their lightweight have extended their use for aircraft brakes. Improved friction and wear properties. The ability to tailor the basic material properties of a Laminate has allowed new approaches to the design of aero elastic flight structures.

DISADVANTAGESome of the associated disadvantages of advanced composites are as follows: High cost of raw materials and fabrication. Composites are more brittle than wrought metals and thus are more easily damaged. Transverse properties may be weak. Matrix is weak, therefore, low toughness. Reuse and disposal may be difficult. Difficult to attach. Repair introduces new problems, for the following reasons: Materials require refrigerated transport and storage and have limited shelf life. Hot curing is necessary in many cases requiring special tooling. Hot or cold curing takes time. Analysis is difficult. Matrix is subject to environmental degradation.

1.2.20- MATRIX MATERIALS:Although it is undoubtedly true that the high strength of composites is largely due to the fiber reinforcement, the importance of matrix material cannot be underestimated as it provides support for the fibers and assists the fibers in carrying the loads. It also provides stability to the composite material. Resin matrix system acts as a binding agent in a structural component in which the fibers are embedded. When too much resin is used, the part is classified as resin rich. On the other hand if there is too little resin, the part is called resin starved. A resin rich part is more susceptible to cracking due to lack of fiber support, whereas a resin starved part is weaker because of void areas and the fact that fibers are not held together and they are not well supported.

1.2.21-FUNCTIONS OF A MATRIX: In a composite material, the matrix material serves the following functions: Holds the fibers together. Protects the fibers from environment. Distributes the loads evenly between fibers so that all fibers are subjected to the same amount of strain. Enhances transverse properties of a laminate. Improves impact and fracture resistance of a component. Helps to avoid propagation of crack growth through the fibers by providing alternate failure path along the interface between the fibers and the matrix. Carry interlaminar shear.

The matrix plays a minor role in the tensile load-carrying capacity of a composite structure. However, selection of a matrix has a major influence on the interlaminar shear as well as in-plane shear properties of the composite material. The interlaminar shear strength is an important design consideration for structures under bending loads, whereas the in-plane shear strength is important under torsion loads. The matrix provides lateral support against the possibility of fiber buckling under compression loading, thus influencing to some extent the compressive strength of the composite material. The interaction between fibers and matrix is also important in designing damage tolerant structures. Finally, the process ability and defects in a composite material depend strongly on the physical and thermal characteristics, such as viscosity, melting point, and curing temperature of the matrix.

1.2.22-PROPERTIES OF A MATRIX:

The needs or desired properties of the matrix which are important for a composite structure are as follows: Reduced moisture absorption. Low shrinkage. Low coefficient of thermal expansion. Good flow characteristics so that it penetrates the fiber bundles completely and eliminates voids during the compacting/curing process. Reasonable strength, modulus and elongation (elongation should be greater than fiber). Must be elastic to transfer load to fibers. Strength at elevated temperature (depending on application). Low temperature capability (depending on application). Excellent chemical resistance (depending on application). Should be easily process able into the final composite shape. Dimensional stability (maintains its shape).

1.2.23-FACTORS CONSIDERED FOR SELECTION OF MATRIX:

In selecting matrix material, following factors may be taken into consideration: The matrix must have a mechanical strength commensurate with that of the reinforcement i.e. both should be compatible. Thus, if a high strength fiber is used as the reinforcement, there is no point using a low strength matrix, which will not transmit stresses efficiently to the reinforcement. The matrix must stand up to the service conditions, viz., temperature, humidity, exposure to ultra-violet environment, exposure to chemic3l atmosphere, abrasion by dust particles, etc. The matrix must be easy to use in the selected fabrication process. Smoke requirements. Life expectancy. The resultant composite should be cost effective.

1.2.24- GENERAL TYPES OF MATRIX MATERIALS:

In general, following general following types of matrix materials are available:

Thermosetting Matrix Materials.

Thermoplastic Matrix Materials.

Carbon Matrix Materials.

Metals Matrix Materials.

Ceramics Matrix Materials.

Glass Matrix Materials.

1.2.25- APPLICATION OF METAL MATRIX COMPOSITES:

Application of metal matrix composites in aerospace, transportation, construction, marine goods, sporting goods, and more recently infrastructure, with construction and transportation being the largest. In general, high-performance but more costly continuous-carbon-fiber composites are used where high strength and stiffness along with light weight are required.

I-AUTOMOTIVE APPLICATION:

Example:- PISTONS AND CYLINDER LINERSAluminum engine blocks typically require cast iron cylinder liners due to poor wear characteristics of aluminum. Porsche is using MMCs for cylinder liners by integrating porous silicon perform into the cast aluminum block, and Honda uses a similar method incorporating alumina and carbon fibers in the bores of die cast aluminum. These practices improve wear characteristics and cooling efficiency over cast iron liners. Providing superior wear resistance, improved cold start emissions, and reduced weight .Aluminum-based composite liners can be cast in place using conventional casting techniques, including sand, permanent mold, die casting, and Centrifugal casting. CONNECTING RODSWith the advent of nanostructure materials, new materials have been developed with exceptional properties exceeding those expected for monolithic alloys or composites containing micron-scale reinforcements. For example, carbon nanotubes have ultrahigh strength and modulus; when included in a matrix, they could impart significant property improvements to the resulting nano-

Fig-1.3 Partial short fiber reinforced light metal diesel pistons

composite. In another example, incorporating only 10 vol% of 50-nm alumina (Al2O3) particles to an aluminum alloy matrix using the powder metallurgy process increased yield strength to 515 MPa. This is 15 times stronger than the base alloy, six times stronger than the base alloy containing 46 vol% of 29-mm Al2O3, and over 1.5 times stronger than AISI 304 stainless steel. Research is in progress at UWM to cast aluminum-base nano-composites with possible strengths on the order of 0.5 to 1 GPa. However, some processing problems need to be resolved, and challenges of scaling up the technology need to be overcome. For components requiring high strength, such as connecting rods, cast aluminum-matrix nano-composites may be ideal to produce near-net-shape components to replace steel, forged aluminum, and titanium components, while reducing reciprocating mass.

SUSPENSIONMany automakers started to use aluminum and light gage steel for suspension components to reduce unsprung weight and improve vehicle dynamics, but many components are still made of cast iron. Components such as control arms or wheel hubs made of strong silicon carbide (SiC) reinforced aluminum or aluminum nano-composites can further improve aluminum alloy designs by improving strength characteristics similar to cast iron, while using less material than similar aluminum arms. Self-lubricating graphite-reinforced aluminum bushings can also be incorporated into control-arm castings to allow for components that do not require service and will last the life of the vehicle.

BRAKESAutomotive disk brakes and brake calipers, typically made of cast iron, are an area where significant weight reduction can be realized. SiC-reinforced aluminum brake rotors are incorporated in vehicles such as the Lotus Elise, Chrysler Prowler, General Motors EV1, Volkswagen Lupo 3L, and the Toyota RAV4-EV.Widespread use of aluminum composite brake rotors requires their costs to come down and improved machinability. UWM developed Aluminum-silicon carbide-graphite composites, aluminum alumina- graphite, and hypereutectic aluminum-silicon graphite alloys with reduced silicon carbide to help overcome cost and machinability barriers. Aluminum-fly ash Composites developed at UWM has been explored to make prototype brake rotors in Australia.

Fig-1.4 Vented passenger car brake disk of particle reinforced aluminum

II-AIRCRAFT AND AEROSPACE APLICATIONS:In military aircraft, low weight is king for performance and payload reasons, and composites often approach 20 to 40 percent of the airframe weight. For decades, helicopters have incorporated glass fiberreinforced rotor blades for improved fatigue resistance, and in recent years helicopter airframes have been built largely of carbon-fiber composites. Military aircraft applications, the first to use high performance continuous-carbon-fiber composites, drove the development of much of the technology now being used by other industries. Both small and large commercial aircraft rely on composites to decrease weight and increase fuel performance, the most striking example being the 50 percent composite airframe for the new Boeing 787 All future Airbus and Boeing aircraft will use large amounts of high-performance composites. Composites are also used extensively in both weight-critical reusable and expendable launch vehicles and satellite structures. Weight savings due to the use of composite materials in aerospace applications generally range from 15 to 25 percent.

Fig. 1.5 Boeing 787 dream liner commercial airplaneIII- WIND TURBINES APLICATIONS:Wind power is the worlds fastest-growing energy source. The blades for large wind turbines are normally made of composites to improve electrical energy generation efficiency. These blades can be as long as 120 ft (37 m) and weigh up to 11,500 lb (5200 kg). In 2007, nearly 50,000 blades for 17,000 turbines were delivered, representing roughly 400 million pounds.

IV-MARINE INDUSTRY APPLICATIONS:Corrosion is a major headache and expense for the marine industry. Composites help minimize these problems, primarily because they do not corrode like metals or rot like wood and more weight reduction.

Fig. 1.6 Wind turbines

1.2.26 NANO-COMPOSITES:A nano-composite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm), or structures having nano-scale repeat distances between the different phases that make up the material. In the broadest sense this definition can include porous media, colloids, gels and copolymers, but is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s) differing in properties due to dissimilarities in structure and chemistry. The mechanical, electrical, thermal, optical, electrochemical, catalytic properties of the nano-composite will differ markedly from that of the component materials. Size limits for these effects have been proposed,