1 Introduction 1.1 DEFINITION Fiber-reinforced composite materials consist of fibers of high strength and modulus embedded in or bonded to a matrix with distinct interfaces(bound- aries)between them.In this form,both fibers and matrix retain their physical and chemical identities,yet they produce a combination of properties that cannot be achieved with either of the constituents acting alone.In general,fibers are the principal load-carrying members,while the surrounding matrix keeps them in the desired location and orientation,acts as a load transfer medium between them, and protects them from environmental damages due to elevated temperatures and humidity,for example.Thus,even though the fibers provide reinforcement for the matrix,the latter also serves a number of useful functions in a fiber- reinforced composite material. The principal fibers in commercial use are various types of glass and carbon as well as Kevlar 49.Other fibers,such as boron,silicon carbide,and aluminum oxide,are used in limited quantities.All these fibers can be incorporated into a matrix either in continuous lengths or in discontinuous(short)lengths.The matrix material may be a polymer,a metal,or a ceramic.Various chemical composi- tions and microstructural arrangements are possible in each matrix category. The most common form in which fiber-reinforced composites are used in structural applications is called a laminate,which is made by stacking a number of thin layers of fibers and matrix and consolidating them into the desired thickness.Fiber orientation in each layer as well as the stacking sequence of various layers in a composite laminate can be controlled to generate a wide range of physical and mechanical properties for the composite laminate. In this book,we focus our attention on the mechanics,performance, manufacturing,and design of fiber-reinforced polymers.Most of the data presented in this book are related to continuous fiber-reinforced epoxy lamin- ates,although other polymeric matrices,including thermoplastic matrices,are also considered.Metal and ceramic matrix composites are comparatively new, but significant developments of these composites have also occurred.They are included in a separate chapter in this book.Injection-molded or reaction injection-molded (RIM)discontinuous fiber-reinforced polymers are not dis- cussed;however,some of the mechanics and design principles included in this book are applicable to these composites as well.Another material of great 2007 by Taylor&Francis Group.LLC
1 Introduction 1.1 DEFINITION Fiber-reinforced composite materials consist of fibers of high strength and modulus embedded in or bonded to a matrix with distinct interfaces (boundaries) between them. In this form, both fibers and matrix retain their physical and chemical identities, yet they produce a combination of properties that cannot be achieved with either of the constituents acting alone. In general, fibers are the principal load-carrying members, while the surrounding matrix keeps them in the desired location and orientation, acts as a load transfer medium between them, and protects them from environmental damages due to elevated temperatures and humidity, for example. Thus, even though the fibers provide reinforcement for the matrix, the latter also serves a number of useful functions in a fiberreinforced composite material. The principal fibers in commercial use are various types of glass and carbon as well as Kevlar 49. Other fibers, such as boron, silicon carbide, and aluminum oxide, are used in limited quantities. All these fibers can be incorporated into a matrix either in continuous lengths or in discontinuous (short) lengths. The matrix material may be a polymer, a metal, or a ceramic. Various chemical compositions and microstructural arrangements are possible in each matrix category. The most common form in which fiber-reinforced composites are used in structural applications is called a laminate, which is made by stacking a number of thin layers of fibers and matrix and consolidating them into the desired thickness. Fiber orientation in each layer as well as the stacking sequence of various layers in a composite laminate can be controlled to generate a wide range of physical and mechanical properties for the composite laminate. In this book, we focus our attention on the mechanics, performance, manufacturing, and design of fiber-reinforced polymers. Most of the data presented in this book are related to continuous fiber-reinforced epoxy laminates, although other polymeric matrices, including thermoplastic matrices, are also considered. Metal and ceramic matrix composites are comparatively new, but significant developments of these composites have also occurred. They are included in a separate chapter in this book. Injection-molded or reaction injection-molded (RIM) discontinuous fiber-reinforced polymers are not discussed; however, some of the mechanics and design principles included in this book are applicable to these composites as well. Another material of great 2007 by Taylor & Francis Group, LLC
commercial interest is classified as particulate composites.The major constitu- ents in these composites are particles of mica,silica,glass spheres,calcium carbonate,and others.In general,these particles do not contribute to the load- carrying capacity of the material and act more like a filler than a reinforcement for the matrix.Particulate composites,by themselves,deserve a special atten- tion and are not addressed in this book. Another type of composites that have the potential of becoming an import- ant material in the future is the nanocomposites.Even though nanocomposites are in the early stages of development,they are now receiving a high degree of attention from academia as well as a large number of industries,including aerospace,automotive,and biomedical industries.The reinforcement in nano- composites is either nanoparticles,nanofibers,or carbon nanotubes.The effect- ive diameter of these reinforcements is of the order of 10m,whereas the effective diameter of the reinforcements used in traditional fiber-reinforced composites is of the order of 10m.The nanocomposites are introduced in Chapter 8. 1.2 GENERAL CHARACTERISTICS Many fiber-reinforced polymers offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials. Because of their low density,the strength-weight ratios and modulus-weight ratios of these composite materials are markedly superior to those of metallic materials (Table 1.1).In addition,fatigue strength as well as fatigue damage tolerance of many composite laminates are excellent.For these reasons,fiber- reinforced polymers have emerged as a major class of structural materials and are either used or being considered for use as substitution for metals in many weight-critical components in aerospace,automotive,and other industries. Traditional structural metals,such as steel and aluminum alloys,are consid- ered isotropic,since they exhibit equal or nearly equal properties irrespective of the direction of measurement.In general,the properties of a fiber-reinforced compos- ite depend strongly on the direction of measurement,and therefore,they are not isotropic materials.For example,the tensile strength and modulus of a unidirec- tionally oriented fiber-reinforced polymer are maximum when these properties are measured in the longitudinal direction of fibers.At any other angle of measure- ment,these properties are lower.The minimum value is observed when they are measured in the transverse direction of fibers,that is,at 90 to the longitudinal direction.Similar angular dependence is observed for other mechanical and thermal properties,such as impact strength,coefficient of thermal expansion (CTE),and thermal conductivity.Bi-or multidirectional reinforcement yields a more balanced set of properties.Although these properties are lower than the longitudinal properties of a unidirectional composite,they still represent a considerable advantage over common structural metals on a unit weight basis. The design of a fiber-reinforced composite structure is considerably more difficult than that of a metal structure,principally due to the difference in its 2007 by Taylor Francis Group,LLC
commercial interest is classified as particulate composites. The major constituents in these composites are particles of mica, silica, glass spheres, calcium carbonate, and others. In general, these particles do not contribute to the loadcarrying capacity of the material and act more like a filler than a reinforcement for the matrix. Particulate composites, by themselves, deserve a special attention and are not addressed in this book. Another type of composites that have the potential of becoming an important material in the future is the nanocomposites. Even though nanocomposites are in the early stages of development, they are now receiving a high degree of attention from academia as well as a large number of industries, including aerospace, automotive, and biomedical industries. The reinforcement in nanocomposites is either nanoparticles, nanofibers, or carbon nanotubes. The effective diameter of these reinforcementsis of the order of 109 m, whereasthe effective diameter of the reinforcements used in traditional fiber-reinforced composites is of the order of 106 m. The nanocomposites are introduced in Chapter 8. 1.2 GENERAL CHARACTERISTICS Many fiber-reinforced polymers offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials. Because of their low density, the strength–weight ratios and modulus–weight ratios of these composite materials are markedly superior to those of metallic materials (Table 1.1). In addition, fatigue strength as well as fatigue damage tolerance of many composite laminates are excellent. For these reasons, fiberreinforced polymers have emerged as a major class of structural materials and are either used or being considered for use as substitution for metals in many weight-critical components in aerospace, automotive, and other industries. Traditional structural metals, such as steel and aluminum alloys, are considered isotropic, since they exhibit equal or nearly equal properties irrespective of the direction of measurement. In general, the properties of a fiber-reinforced composite depend strongly on the direction of measurement, and therefore, they are not isotropic materials. For example, the tensile strength and modulus of a unidirectionally oriented fiber-reinforced polymer are maximum when these properties are measured in the longitudinal direction of fibers. At any other angle of measurement, these properties are lower. The minimum value is observed when they are measured in the transverse direction of fibers, that is, at 908 to the longitudinal direction. Similar angular dependence is observed for other mechanical and thermal properties, such as impact strength, coefficient of thermal expansion (CTE), and thermal conductivity. Bi- or multidirectional reinforcement yields a more balanced set of properties. Although these properties are lower than the longitudinal properties of a unidirectional composite, they still represent a considerable advantage over common structural metals on a unit weight basis. The design of a fiber-reinforced composite structure is considerably more difficult than that of a metal structure, principally due to the difference in its 2007 by Taylor & Francis Group, LLC
TABLE 1.1 Taykr Francis Group. Tensile Properties of Some Metallic and Structural Composite Materials Ratio of Tensile Density, Modulus, Tensile Strength, Yield Strength, Ratio of Modulus Strength to Material g/cm3 GPa (Msi) MPa(ksi) MPa (ksi) to Weight,b 105 m Weight,b 103m SAE 1010 steel (cold-worked) 7.87 207(30) 365(53) 303(44) 2.68 4.72 AISI 4340 steel (quenched and tempered) 7.87 207(30) 1722(250) 1515(220) 2.68 22.3 6061-T6 aluminum alloy 2.70 68.9(10) 310(45) 275(40) 2.60 11.7 7178-T6 aluminum alloy 2.70 68.9(10) 606(88) 537(78) 2.60 22.9 Ti-6A1-4V titanium alloy (aged) 4.43 110(16) 1171(170) 1068(155 2.53 26.9 17-7 PH stainless steel (aged) 7.87 196(28.5) 1619(235) 1515(220) 2.54 21.0 INCO 718 nickel alloy (aged) 8.2 207(30) 1399(203) 1247(181) 2.57 17.4 High-strength carbon fiber-epoxy 1.55 137.8(20) 1550(225) 9.06 101.9 matrix (unidirectional)" High-modulus carbon fiber-epoxy 1.63 215(31.2) 1240(180) 13.44 77.5 matrix (unidirectional) E-glass fiber-epoxy matrix(unidirectional) 1.85 39.3(5.7) 965(140) 2.16 53.2 Kevlar 49 fiber-epoxy matrix (unidirectional) 1.38 75.8(11) 1378(200) 5.60 101.8 Boron fiber-6061 Al alloy matrix (annealed) 2.35 220(32) 1109(161) Carbon fiber-epoxy matrix (quasi-isotropic) 1.55 45.5(6.6) 579(84) 二 9.54 48.1 2.99 38 Sheet-molding compound(SMC) 1.87 15.8(2.3) 164(23.8) 0.86 89 composite (isotropic) "For unidirectional composites,the fibers are unidirectional and the reported modulus and tensile strength values are measured in the direction of fibers. that is,the longitudinal direction of the composite. The modulus-weight ratio and the strength-weight ratios are obtained by dividing the absolute values with the specific weight of the respective material Specific weight is defined as weight per unit volume.It is obtained by multiplying density with the acceleration due to gravity
TABLE 1.1 Tensile Properties of Some Metallic and Structural Composite Materials Materiala Density, g=cm3 Modulus, GPa (Msi) Tensile Strength, MPa (ksi) Yield Strength, MPa (ksi) Ratio of Modulus to Weight,b 106 m Ratio of Tensile Strength to Weight,b 103 m SAE 1010 steel (cold-worked) 7.87 207 (30) 365 (53) 303 (44) 2.68 4.72 AISI 4340 steel (quenched and tempered) 7.87 207 (30) 1722 (250) 1515 (220) 2.68 22.3 6061-T6 aluminum alloy 2.70 68.9 (10) 310 (45) 275 (40) 2.60 11.7 7178-T6 aluminum alloy 2.70 68.9 (10) 606 (88) 537 (78) 2.60 22.9 Ti-6A1-4V titanium alloy (aged) 4.43 110 (16) 1171 (170) 1068 (155) 2.53 26.9 17-7 PH stainless steel (aged) 7.87 196 (28.5) 1619 (235) 1515 (220) 2.54 21.0 INCO 718 nickel alloy (aged) 8.2 207 (30) 1399 (203) 1247 (181) 2.57 17.4 High-strength carbon fiber–epoxy matrix (unidirectional)a 1.55 137.8 (20) 1550 (225) — 9.06 101.9 High-modulus carbon fiber–epoxy matrix (unidirectional) 1.63 215 (31.2) 1240 (180) — 13.44 77.5 E-glass fiber–epoxy matrix (unidirectional) 1.85 39.3 (5.7) 965 (140) — 2.16 53.2 Kevlar 49 fiber–epoxy matrix (unidirectional) 1.38 75.8 (11) 1378 (200) — 5.60 101.8 Boron fiber-6061 A1 alloy matrix (annealed) 2.35 220 (32) 1109 (161) — 9.54 48.1 Carbon fiber–epoxy matrix (quasi-isotropic) 1.55 45.5 (6.6) 579 (84) — 2.99 38 Sheet-molding compound (SMC) composite (isotropic) 1.87 15.8 (2.3) 164 (23.8) 0.86 8.9 a For unidirectional composites, the fibers are unidirectional and the reported modulus and tensile strength values are measured in the direction of fibers, that is, the longitudinal direction of the composite. b The modulus–weight ratio and the strength–weight ratios are obtained by dividing the absolute values with the specific weight of the respective material. Specific weight is defined as weight per unit volume. It is obtained by multiplying density with the acceleration due to gravity. 2007 by Taylor & Francis Group, LLC
properties in different directions.However,the nonisotropic nature of a fiber- reinforced composite material creates a unique opportunity of tailoring its properties according to the design requirements.This design flexibility can be used to selectively reinforce a structure in the directions of major stresses, increase its stiffness in a preferred direction,fabricate curved panels without any secondary forming operation,or produce structures with zero coefficients of thermal expansion. The use of fiber-reinforced polymer as the skin material and a lightweight core,such as aluminum honeycomb,plastic foam,metal foam,and balsa wood, to build a sandwich beam,plate,or shell provides another degree of design flexibility that is not easily achievable with metals.Such sandwich construction can produce high stiffness with very little,if any,increase in weight.Another sandwich construction in which the skin material is an aluminum alloy and the core material is a fiber-reinforced polymer has found widespread use in aircrafts and other applications,primarily due to their higher fatigue performance and damage tolerance than aluminum alloys. In addition to the directional dependence of properties,there are a number of other differences between structural metals and fiber-reinforced composites. For example,metals in general exhibit yielding and plastic deformation.Most fiber-reinforced composites are elastic in their tensile stress-strain character- istics.However,the heterogeneous nature of these materials provides mechan- isms for energy absorption on a microscopic scale,which is comparable to the yielding process.Depending on the type and severity of external loads,a composite laminate may exhibit gradual deterioration in properties but usually would not fail in a catastrophic manner.Mechanisms of damage development and growth in metal and composite structures are also quite different and must be carefully considered during the design process when the metal is substituted with a fiber-reinforced polymer. Coefficient of thermal expansion(CTE)for many fiber-reinforced composites is much lower than that for metals (Table 1.2).As a result,composite structures may exhibit a better dimensional stability over a wide temperature range.How- ever,the differences in thermal expansion between metals and composite materials may create undue thermal stresses when they are used in conjunction,for example, near an attachment.In some applications,such as electronic packaging,where quick and effective heat dissipation is needed to prevent component failure or malfunctioning due to overheating and undesirable temperature rise,thermal conductivity is an important material property to consider.In these applications, some fiber-reinforced composites may excel over metals because of the combin- ation of their high thermal conductivity-weight ratio (Table 1.2)and low CTE.On the other hand,electrical conductivity of fiber-reinforced polymers is,in general, lower than that of metals.The electric charge build up within the material because of low electrical conductivity can lead to problems such as radio frequency interference(RFD)and damage due to lightning strike. 2007 by Taylor Francis Group,LLC
properties in different directions. However, the nonisotropic nature of a fiberreinforced composite material creates a unique opportunity of tailoring its properties according to the design requirements. This design flexibility can be used to selectively reinforce a structure in the directions of major stresses, increase its stiffness in a preferred direction, fabricate curved panels without any secondary forming operation, or produce structures with zero coefficients of thermal expansion. The use of fiber-reinforced polymer as the skin material and a lightweight core, such as aluminum honeycomb, plastic foam, metal foam, and balsa wood, to build a sandwich beam, plate, or shell provides another degree of design flexibility that is not easily achievable with metals. Such sandwich construction can produce high stiffness with very little, if any, increase in weight. Another sandwich construction in which the skin material is an aluminum alloy and the core material is a fiber-reinforced polymer has found widespread use in aircrafts and other applications, primarily due to their higher fatigue performance and damage tolerance than aluminum alloys. In addition to the directional dependence of properties, there are a number of other differences between structural metals and fiber-reinforced composites. For example, metals in general exhibit yielding and plastic deformation. Most fiber-reinforced composites are elastic in their tensile stress–strain characteristics. However, the heterogeneous nature of these materials provides mechanisms for energy absorption on a microscopic scale, which is comparable to the yielding process. Depending on the type and severity of external loads, a composite laminate may exhibit gradual deterioration in properties but usually would not fail in a catastrophic manner. Mechanisms of damage development and growth in metal and composite structures are also quite different and must be carefully considered during the design process when the metal is substituted with a fiber-reinforced polymer. Coefficient of thermal expansion (CTE) for many fiber-reinforced composites is much lower than that for metals (Table 1.2). As a result, composite structures may exhibit a better dimensional stability over a wide temperature range. However, the differences in thermal expansion between metals and composite materials may create undue thermal stresses when they are used in conjunction, for example, near an attachment. In some applications, such as electronic packaging, where quick and effective heat dissipation is needed to prevent component failure or malfunctioning due to overheating and undesirable temperature rise, thermal conductivity is an important material property to consider. In these applications, some fiber-reinforced composites may excel over metals because of the combination of their high thermal conductivity–weight ratio (Table 1.2) and low CTE. On the other hand, electrical conductivity of fiber-reinforced polymers is, in general, lower than that of metals. The electric charge build up within the material because of low electrical conductivity can lead to problems such as radio frequency interference (RFI) and damage due to lightning strike. 2007 by Taylor & Francis Group, LLC
TABLE 1.2 Thermal Properties of a Few Selected Metals and Composite Materials Ratio of Coefficient Thermal of Thermal Thermal Conductivity Density Expansion Conductivity to Weight Material (g/cm3) (10-6/C) (W/mK) (10-3m/s3K) Plain carbon steels 7.87 11.7 52 6.6 Copper 8.9 17 388 43.6 Aluminum alloys 2.7 23.5 130-220 48.1-81.5 Ti-6Al-4V titanium alloy 4.43 8.6 6.7 1.51 Invar 8.05 1.6 10 1.24 K1100 carbon fiber-epoxy matrix 1.8 -1.1 300 166.7 Glass fiber-epoxy matrix 2.1 11-20 0.16-0.26 0.08-0.12 SiC particle-reinforced aluminum 3 6.2-7.3 170-220 56.7-73.3 Another unique characteristic of many fiber-reinforced composites is their high internal damping.This leads to better vibrational energy absorption within the material and results in reduced transmission of noise and vibrations to neighboring structures.High damping capacity of composite materials can be beneficial in many automotive applications in which noise,vibration,and harshness (NVH)are critical issues for passenger comfort.High damping capacity is also useful in many sporting goods applications. An advantage attributed to fiber-reinforced polymers is their noncorroding behavior.However,many fiber-reinforced polymers are capable of absorbing moisture or chemicals from the surrounding environment,which may create dimensional changes or adverse internal stresses in the material.If such behav- ior is undesirable in an application,the composite surface must be protected from moisture or chemicals by an appropriate paint or coating.Among other environmental factors that may cause degradation in the mechanical properties of some polymer matrix composites are elevated temperatures,corrosive fluids, and ultraviolet rays.In metal matrix composites,oxidation of the matrix as well as adverse chemical reaction between fibers and the matrix are of great concern in high-temperature applications. The manufacturing processes used with fiber-reinforced polymers are dif- ferent from the traditional manufacturing processes used for metals,such as casting,forging,and so on.In general,they require significantly less energy and lower pressure or force than the manufacturing processes used for metals.Parts integration and net-shape or near net-shape manufacturing processes are also great advantages of using fiber-reinforced polymers.Parts integration reduces the number of parts,the number of manufacturing operations,and also,the number of assembly operations.Net-shape or near net-shape manufacturing 2007 by Taylor Francis Group.LLC
Another unique characteristic of many fiber-reinforced composites is their high internal damping. This leads to better vibrational energy absorption within the material and results in reduced transmission of noise and vibrations to neighboring structures. High damping capacity of composite materials can be beneficial in many automotive applications in which noise, vibration, and harshness (NVH) are critical issues for passenger comfort. High damping capacity is also useful in many sporting goods applications. An advantage attributed to fiber-reinforced polymers is their noncorroding behavior. However, many fiber-reinforced polymers are capable of absorbing moisture or chemicals from the surrounding environment, which may create dimensional changes or adverse internal stresses in the material. If such behavior is undesirable in an application, the composite surface must be protected from moisture or chemicals by an appropriate paint or coating. Among other environmental factors that may cause degradation in the mechanical properties of some polymer matrix composites are elevated temperatures, corrosive fluids, and ultraviolet rays. In metal matrix composites, oxidation of the matrix as well as adverse chemical reaction between fibers and the matrix are of great concern in high-temperature applications. The manufacturing processes used with fiber-reinforced polymers are different from the traditional manufacturing processes used for metals, such as casting, forging, and so on. In general, they require significantly less energy and lower pressure or force than the manufacturing processes used for metals. Parts integration and net-shape or near net-shape manufacturing processes are also great advantages of using fiber-reinforced polymers. Parts integration reduces the number of parts, the number of manufacturing operations, and also, the number of assembly operations. Net-shape or near net-shape manufacturing TABLE 1.2 Thermal Properties of a Few Selected Metals and Composite Materials Material Density (g=cm3 ) Coefficient of Thermal Expansion (106 =8C) Thermal Conductivity (W=m8K) Ratio of Thermal Conductivity to Weight (103 m4 =s 3 8K) Plain carbon steels 7.87 11.7 52 6.6 Copper 8.9 17 388 43.6 Aluminum alloys 2.7 23.5 130–220 48.1–81.5 Ti-6Al-4V titanium alloy 4.43 8.6 6.7 1.51 Invar 8.05 1.6 10 1.24 K1100 carbon fiber–epoxy matrix 1.8 1.1 300 166.7 Glass fiber–epoxy matrix 2.1 11–20 0.16–0.26 0.08–0.12 SiC particle-reinforced aluminum 3 6.2–7.3 170–220 56.7–73.3 2007 by Taylor & Francis Group, LLC
processes,such as filament winding and pultrusion,used for making many fiber-reinforced polymer parts,either reduce or eliminate the finishing oper- ations such as machining and grinding,which are commonly required as finishing operations for cast or forged metallic parts. 1.3 APPLICATIONS Commercial and industrial applications of fiber-reinforced polymer composites are so varied that it is impossible to list them all.In this section,we highlight only the major structural application areas,which include aircraft,space, automotive,sporting goods,marine,and infrastructure.Fiber-reinforced poly- mer composites are also used in electronics (e.g.,printed circuit boards), building construction (e.g.,floor beams),furniture (e.g.,chair springs),power industry (e.g.,transformer housing),oil industry (e.g.,offshore oil platforms and oil sucker rods used in lifting underground oil),medical industry (e.g.,bone plates for fracture fixation,implants,and prosthetics),and in many industrial prod- ucts,such as step ladders,oxygen tanks,and power transmission shafts.Poten- tial use of fiber-reinforced composites exists in many engineering fields.Putting them to actual use requires careful design practice and appropriate process development based on the understanding of their unique mechanical,physical, and thermal characteristics. 1.3.1 AIRCRAFT AND MILITARY APPLICATIONS The major structural applications for fiber-reinforced composites are in the field of military and commercial aircrafts,for which weight reduction is critical for higher speeds and increased payloads.Ever since the production application of boron fiber-reinforced epoxy skins for F-14 horizontal stabilizers in 1969, the use of fiber-reinforced polymers has experienced a steady growth in the aircraft industry.With the introduction of carbon fibers in the 1970s,carbon fiber-reinforced epoxy has become the primary material in many wing,fuselage, and empennage components (Table 1.3).The structural integrity and durability of these early components have built up confidence in their performance and prompted developments of other structural aircraft components,resulting in an increasing amount of composites being used in military aircrafts.For example, the airframe of AV-8B,a vertical and short take-off and landing (VSTOL) aircraft introduced in 1982,contains nearly 25%by weight of carbon fiber- reinforced epoxy.The F-22 fighter aircraft also contains ~25%by weight of carbon fiber-reinforced polymers;the other major materials are titanium(39%) and aluminum (16%).The outer skin of B-2 (Figure 1.1)and other stealth aircrafts is almost all made of carbon fiber-reinforced polymers.The stealth characteristics of these aircrafts are due to the use of carbon fibers,special coatings,and other design features that reduce radar reflection and heat radiation. 2007 by Taylor Francis Group,LLC
processes, such as filament winding and pultrusion, used for making many fiber-reinforced polymer parts, either reduce or eliminate the finishing operations such as machining and grinding, which are commonly required as finishing operations for cast or forged metallic parts. 1.3 APPLICATIONS Commercial and industrial applications of fiber-reinforced polymer composites are so varied that it is impossible to list them all. In this section, we highlight only the major structural application areas, which include aircraft, space, automotive, sporting goods, marine, and infrastructure. Fiber-reinforced polymer composites are also used in electronics (e.g., printed circuit boards), building construction (e.g., floor beams), furniture (e.g., chair springs), power industry (e.g., transformer housing), oil industry (e.g., offshore oil platforms and oil suckerrods used in lifting underground oil), medical industry (e.g., bone plates for fracture fixation, implants, and prosthetics), and in many industrial products, such as step ladders, oxygen tanks, and power transmission shafts. Potential use of fiber-reinforced composites exists in many engineering fields. Putting them to actual use requires careful design practice and appropriate process development based on the understanding of their unique mechanical, physical, and thermal characteristics. 1.3.1 AIRCRAFT AND MILITARY APPLICATIONS The major structural applications for fiber-reinforced composites are in the field of military and commercial aircrafts, for which weight reduction is critical for higher speeds and increased payloads. Ever since the production application of boron fiber-reinforced epoxy skins for F-14 horizontal stabilizers in 1969, the use of fiber-reinforced polymers has experienced a steady growth in the aircraft industry. With the introduction of carbon fibers in the 1970s, carbon fiber-reinforced epoxy has become the primary material in many wing, fuselage, and empennage components (Table 1.3). The structural integrity and durability of these early components have built up confidence in their performance and prompted developments of other structural aircraft components, resulting in an increasing amount of composites being used in military aircrafts. For example, the airframe of AV-8B, a vertical and short take-off and landing (VSTOL) aircraft introduced in 1982, contains nearly 25% by weight of carbon fiberreinforced epoxy. The F-22 fighter aircraft also contains ~25% by weight of carbon fiber-reinforced polymers; the other major materials are titanium (39%) and aluminum (16%). The outer skin of B-2 (Figure 1.1) and other stealth aircrafts is almost all made of carbon fiber-reinforced polymers. The stealth characteristics of these aircrafts are due to the use of carbon fibers, special coatings, and other design features that reduce radar reflection and heat radiation. 2007 by Taylor & Francis Group, LLC
TABLE 1.3 Early Applications of Fiber-Reinforced Polymers in Military Aircrafts Overall Weight Saving Over Aircraft Component Material Metal Component(%) F.14(1969) Skin on the horizontal stabilizer Boron fiber-epoxy 19 box F.11 Under the wing fairings Carbon fiber-epoxy F.15(1975) Fin,rudder,and stabilizer skins Boron fiber-epoxy 25 F.16(1977) Skins on vertical fin box.fin Carbon fiber-epoxy 2 leading edge F/A-18(1978) Wing skins,horizontal and Carbon fiber-epoxy 35 vertical tail boxes;wing and tail control surfaces,etc. AV-8B(1982) Wing skins and substructures; Carbon fiber-epoxy 25 forward fuselage;horizontal stabilizer;flaps;ailerons Source:Adapted from Riggs,J.P..Mater.Soc.,8.351,1984. The composite applications on commercial aircrafts began with a few selective secondary structural components,all of which were made of a high- strength carbon fiber-reinforced epoxy (Table 1.4).They were designed and produced under the NASA Aircraft Energy Efficiency (ACEE)program and were installed in various airplanes during 1972-1986 [1].By 1987,350 compos- ite components were placed in service in various commercial aircrafts,and over the next few years,they accumulated millions of flight hours.Periodic inspec- tion and evaluation of these components showed some damages caused by ground handling accidents,foreign object impacts,and lightning strikes. FIGURE 1.1 Stealth aircraft (note that the carbon fibers in the construction of the aircraft contributes to its stealth characteristics). 2007 by Taylor Francis Group.LLC
The composite applications on commercial aircrafts began with a few selective secondary structural components, all of which were made of a highstrength carbon fiber-reinforced epoxy (Table 1.4). They were designed and produced under the NASA Aircraft Energy Efficiency (ACEE) program and were installed in various airplanes during 1972–1986 [1]. By 1987, 350 composite components were placed in service in various commercial aircrafts, and over the next few years, they accumulated millions of flight hours. Periodic inspection and evaluation of these components showed some damages caused by ground handling accidents, foreign object impacts, and lightning strikes. TABLE 1.3 Early Applications of Fiber-Reinforced Polymers in Military Aircrafts Aircraft Component Material Overall Weight Saving Over Metal Component (%) F-14 (1969) Skin on the horizontal stabilizer box Boron fiber–epoxy 19 F-11 Under the wing fairings Carbon fiber–epoxy F-15 (1975) Fin, rudder, and stabilizer skins Boron fiber–epoxy 25 F-16 (1977) Skins on vertical fin box, fin leading edge Carbon fiber–epoxy 23 F=A-18 (1978) Wing skins, horizontal and vertical tail boxes; wing and tail control surfaces, etc. Carbon fiber–epoxy 35 AV-8B (1982) Wing skins and substructures; forward fuselage; horizontal stabilizer; flaps; ailerons Carbon fiber–epoxy 25 Source: Adapted from Riggs, J.P., Mater. Soc., 8, 351, 1984. FIGURE 1.1 Stealth aircraft (note that the carbon fibers in the construction of the aircraft contributes to its stealth characteristics). 2007 by Taylor & Francis Group, LLC
TABLE 1.4 Early Applications of Fiber-Reinforced Polymers in Commercial Aircrafts Weight Aircraft Component Weight(Ib) Reduction (% Comments Boeing 727 Elevator face sheets 98 25 10 units installed in 1980 737 Horizontal stabilizer 204 737 Wing spoilers 3 Installed in 1973 756 Ailerons,rudders. 3340 (total) elevators,fairings,etc. MeDonnell-Douglas DC-10 Upper rudder 67 26 13 units installed in 1976 DC-10 Vertical stabilizer 834 17 Lockheed L-1011 Aileron 107 23 10 units installed in 1981 L-1011 Vertical stabilizer 622 25 Apart from these damages,there was no degradation of residual strengths due to either fatigue or environmental exposure.A good correlation was found between the on-ground environmental test program and the performance of the composite components after flight exposure. Airbus was the first commercial aircraft manufacturer to make extensive use of composites in their A310 aircraft,which was introduced in 1987.The composite components weighed about 10%of the aircraft's weight and included such components as the lower access panels and top panels of the wing leading edge,outer deflector doors,nose wheel doors,main wheel leg fairing doors,engine cowling panels,elevators and fin box,leading and trailing edges of fins,flap track fairings,flap access doors,rear and forward wing-body fairings,pylon fairings,nose radome,cooling air inlet fairings,tail leading edges,upper surface skin panels above the main wheel bay,glide slope antenna cover,and rudder.The composite vertical stabilizer,which is 8.3 m high by 7.8 m wide at the base,is about 400 kg lighter than the aluminum vertical stabilizer previously used [2].The Airbus A320,introduced in 1988, was the first commercial aircraft to use an all-composite tail,which includes the tail cone,vertical stabilizer,and horizontal stabilizer.Figure 1.2 schemat- ically shows the composite usage in Airbus A380 introduced in 2006.About 25%of its weight is made of composites.Among the major composite com- ponents in A380 are the central torsion box (which links the left and right wings under the fuselage),rear-pressure bulkhead (a dome-shaped partition that separates the passenger cabin from the rear part of the plane that is not pressurized),the tail,and the flight control surfaces,such as the flaps,spoilers, and ailerons. 2007 by Taylor Francis Group,LLC
Apart from these damages, there was no degradation of residual strengths due to either fatigue or environmental exposure. A good correlation was found between the on-ground environmental test program and the performance of the composite components after flight exposure. Airbus was the first commercial aircraft manufacturer to make extensive use of composites in their A310 aircraft, which was introduced in 1987. The composite components weighed about 10% of the aircraft’s weight and included such components as the lower access panels and top panels of the wing leading edge, outer deflector doors, nose wheel doors, main wheel leg fairing doors, engine cowling panels, elevators and fin box, leading and trailing edges of fins, flap track fairings, flap access doors, rear and forward wing–body fairings, pylon fairings, nose radome, cooling air inlet fairings, tail leading edges, upper surface skin panels above the main wheel bay, glide slope antenna cover, and rudder. The composite vertical stabilizer, which is 8.3 m high by 7.8 m wide at the base, is about 400 kg lighter than the aluminum vertical stabilizer previously used [2]. The Airbus A320, introduced in 1988, was the first commercial aircraft to use an all-composite tail, which includes the tail cone, vertical stabilizer, and horizontal stabilizer. Figure 1.2 schematically shows the composite usage in Airbus A380 introduced in 2006. About 25% of its weight is made of composites. Among the major composite components in A380 are the central torsion box (which links the left and right wings under the fuselage), rear-pressure bulkhead (a dome-shaped partition that separates the passenger cabin from the rear part of the plane that is not pressurized), the tail, and the flight control surfaces, such as the flaps, spoilers, and ailerons. TABLE 1.4 Early Applications of Fiber-Reinforced Polymers in Commercial Aircrafts Aircraft Component Weight (lb) Weight Reduction (%) Comments Boeing 727 Elevator face sheets 98 25 10 units installed in 1980 737 Horizontal stabilizer 204 22 737 Wing spoilers — 37 Installed in 1973 756 Ailerons, rudders, elevators, fairings, etc. 3340 (total) 31 McDonnell-Douglas DC-10 Upper rudder 67 26 13 units installed in 1976 DC-10 Vertical stabilizer 834 17 Lockheed L-1011 Aileron 107 23 10 units installed in 1981 L-1011 Vertical stabilizer 622 25 2007 by Taylor & Francis Group, LLC
Wing box Vertical Outer wing stabilizer Ailerons Pressure bulkhead Tail cone Flap track fairings Horizontal Outer flap stabilizer Fixed leading edge 0 Keel beam upper and lower panels 0 Outer boxes Belly fairing skins Over-wing panel Radome Trailing edge upper and lower panels and shroud box Nose landing Main and 0 Spoilers gear doors center landing Main landing gear doors gear leg fairing Pylon fairings, door nacelles, and cowlings Central torsion box FIGURE 1.2 Use of fiber-reinforced polymer composites in Airbus 380. Starting with Boeing 777,which was first introduced in 1995,Boeing has started making use of composites in the empennage(which include horizontal stabilizer,vertical stabilizer,elevator,and rudder),most of the control surfaces, engine cowlings,and fuselage floor beams (Figure 1.3).About 10%of Boeing 777's structural weight is made of carbon fiber-reinforced epoxy and about 50% is made of aluminum alloys.About 50%of the structural weight of Boeing's Leading and Fin torque box Outboard aileron trailing edge panels Outboard flap Rudder Wing fixed leading edge Trailing edge panels Elevator Stabilizer torque box Strut-Fwd and aft fairing Floor beams Wing landing gear doors Flaps Flaperon Inboard and outboard spoilers Nose radome Nose gear doors Engine cowlings FIGURE 1.3 Use of fiber-reinforced polymer composites in Boeing 777. 2007 by Taylor Francis Group.LLC
Starting with Boeing 777, which was first introduced in 1995, Boeing has started making use of composites in the empennage (which include horizontal stabilizer, vertical stabilizer, elevator, and rudder), most of the control surfaces, engine cowlings, and fuselage floor beams (Figure 1.3). About 10% of Boeing 777’s structural weight is made of carbon fiber-reinforced epoxy and about 50% is made of aluminum alloys. About 50% of the structural weight of Boeing’s Outer wing Ailerons Flap track fairings Outer flap Radome Fixed leading edge upper and lower panels Main landing gear leg fairing door Main and center landing gear doors Nose landing gear doors Central torsion box Pylon fairings, nacelles, and cowlings Pressure bulkhead Keel beam Tail cone Vertical stabilizer Horizontal stabilizer Outer boxes Over-wing panel Belly fairing skins Trailing edge upper and lower panels and shroud box Spoilers Wing box FIGURE 1.2 Use of fiber-reinforced polymer composites in Airbus 380. Rudder Fin torque box Elevator Stabilizer torque box Floor beams Wing landing gear doors Flaps Flaperon Inboard and outboard spoilers Engine cowlings Nose gear doors Nose radome Strut–Fwd and aft fairing Wing fixed leading edge Outboard aileron Outboard flap Trailing edge panels Leading and trailing edge panels FIGURE 1.3 Use of fiber-reinforced polymer composites in Boeing 777. 2007 by Taylor & Francis Group, LLC
next line of airplanes,called the Boeing 787 Dreamliner,will be made of carbon fiber-reinforced polymers.The other major materials in Boeing 787 will be aluminum alloys (20%),titanium alloys (15%),and steel (10%).Two of the major composite components in 787 will be the fuselage and the forward section,both of which will use carbon fiber-reinforced epoxy as the major material of construction. There are several pioneering examples of using larger quantities of com- posite materials in smaller aircrafts.One of these examples is the Lear Fan 2100,a business aircraft built in 1983,in which carbon fiber-epoxy and Kevlar 49 fiber-epoxy accounted for ~70%of the aircraft's airframe weight.The composite components in this aircraft included wing skins,main spar,fuselage, empennage,and various control surfaces [3].Another example is the Rutan Voyager(Figure 1.4),which was an all-composite airplane and made the first- ever nonstop flight around the world in 1986.To travel 25,000 miles without refueling,the Voyager airplane had to be extremely light and contain as much fuel as needed. Fiber-reinforced polymers are used in many military and commercial heli- copters for making baggage doors,fairings,vertical fins,tail rotor spars,and so on.One key helicopter application of composite materials is the rotor blades. Carbon or glass fiber-reinforced epoxy is used in this application.In addition to significant weight reduction over aluminum,they provide a better control over the vibration characteristics of the blades.With aluminum,the critical flopping FIGURE 1.4 Rutan Voyager all-composite plane. 2007 by Taylor Francis Group,LLC
next line of airplanes, called the Boeing 787 Dreamliner, will be made of carbon fiber-reinforced polymers. The other major materials in Boeing 787 will be aluminum alloys (20%), titanium alloys (15%), and steel (10%). Two of the major composite components in 787 will be the fuselage and the forward section, both of which will use carbon fiber-reinforced epoxy as the major material of construction. There are several pioneering examples of using larger quantities of composite materials in smaller aircrafts. One of these examples is the Lear Fan 2100, a business aircraft built in 1983, in which carbon fiber–epoxy and Kevlar 49 fiber–epoxy accounted for ~70% of the aircraft’s airframe weight. The composite components in this aircraft included wing skins, main spar, fuselage, empennage, and various control surfaces [3]. Another example is the Rutan Voyager (Figure 1.4), which was an all-composite airplane and made the firstever nonstop flight around the world in 1986. To travel 25,000 miles without refueling, the Voyager airplane had to be extremely light and contain as much fuel as needed. Fiber-reinforced polymers are used in many military and commercial helicopters for making baggage doors, fairings, vertical fins, tail rotor spars, and so on. One key helicopter application of composite materials is the rotor blades. Carbon or glass fiber-reinforced epoxy is used in this application. In addition to significant weight reduction over aluminum, they provide a better control over the vibration characteristics of the blades. With aluminum, the critical flopping FIGURE 1.4 Rutan Voyager all-composite plane. 2007 by Taylor & Francis Group, LLC
