《纺织复合材料》课程参考文献（Fiber-Reinforced Composites，THIRD EDITION）01 Introduction.pdf

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

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