《纺织复合材料》课程参考文献（Fiber-Reinforced Composites，THIRD EDITION）02 Materials

500 24℃(75F)】 400 2,760 400℃(750℉) 300 500℃(930℉) 200 600℃(1,110F) 1,380 ssens ejlsue1 100 0 0 10 100 1.000 10,000 Load duration(min) FIGURE 2.11 Reduction of tensile stress in E-glass fibers as a function of time at various temperatures.(After Otto,W.H.,Properties of glass fibers at elevated temperatures, Owens Corning Fiberglas Corporation,AD 228551,1958.) equipment,tends to reduce it to values that are in the range of 1.72-2.07 GPa (250,000-300,000 psi).Strength degradation is increased as the surface flaws grow under cyclic loads,which is one of the major disadvantages of using glass fibers in fatigue applications.Surface compressive stresses obtained by alkali ion exchange [3]or elimination of surface flaws by chemical etching may reduce the problem;however,commercial glass fibers are not available with any such surface modifications. The tensile strength of glass fibers is also reduced in the presence of water or under sustained loads(static fatigue).Water bleaches out the alkalis from the surface and deepens the surface flaws already present in fibers.Under sustained loads,the growth of surface flaws is accelerated owing to stress corrosion by atmospheric moisture.As a result,the tensile strength of glass fibers is decreased with increasing time of load duration (Figure 2.11). 2.1.2 CARBON FIBERS Carbon fibers are commercially available with a variety of tensile modulus values ranging from 207 GPa (30X 10 psi)on the low side to 1035 GPa (150 x 10 psi)on the high side.In general,the low-modulus fibers have lower density,lower cost,higher tensile and compressive strengths,and higher tensile strains-to-failure than the high-modulus fibers.Among the advantages of carbon fibers are their exceptionally high tensile strength-weight ratios as well as tensile modulus-weight ratios,very low coefficient of linear thermal expansion (which provides dimensional stability in such applications as space antennas),high fatigue strengths,and high thermal conductivity(which is even 2007 by Taylor Francis Group,LLC

equipment, tends to reduce it to values that are in the range of 1.72–2.07 GPa (250,000–300,000 psi). Strength degradation is increased as the surface flaws grow under cyclic loads, which is one of the major disadvantages of using glass fibers in fatigue applications. Surface compressive stresses obtained by alkali ion exchange [3] or elimination of surface flaws by chemical etching may reduce the problem; however, commercial glass fibers are not available with any such surface modifications. The tensile strength of glass fibers is also reduced in the presence of water or under sustained loads (static fatigue). Water bleaches out the alkalis from the surface and deepens the surface flaws already present in fibers. Under sustained loads, the growth of surface flaws is accelerated owing to stress corrosion by atmospheric moisture. As a result, the tensile strength of glass fibers is decreased with increasing time of load duration (Figure 2.11). 2.1.2 CARBON FIBERS Carbon fibers are commercially available with a variety of tensile modulus values ranging from 207 GPa (30 3 106 psi) on the low side to 1035 GPa (150 3 106 psi) on the high side. In general, the low-modulus fibers have lower density, lower cost, higher tensile and compressive strengths, and higher tensile strains-to-failure than the high-modulus fibers. Among the advantages of carbon fibers are their exceptionally high tensile strength–weight ratios as well as tensile modulus–weight ratios, very low coefficient of linear thermal expansion (which provides dimensional stability in such applications as space antennas), high fatigue strengths, and high thermal conductivity (which is even 500 Tensile stress (103 psi) 24C (75F) 400C (750F) 500C (930F) 600C (1,110F) 400 300 200 100 0 1 10 100 Load duration (min) Tensile stress (MPa) 1,000 10,000 2,760 1,380 0 FIGURE 2.11 Reduction of tensile stress in E-glass fibers as a function of time at various temperatures. (After Otto, W.H., Properties of glass fibers at elevated temperatures, Owens Corning Fiberglas Corporation, AD 228551, 1958.)
2007 by Taylor & Francis Group, LLC.

3.4A 1.42A/ FIGURE 2.12 Arrangement of carbon atoms in a graphite crystal. higher than that of copper).The disadvantages are their low strain-to-failure,low impact resistance,and high electrical conductivity,which may cause"shorting" in unprotected electrical machinery.Their high cost has so far excluded them from widespread commercial applications.They are used mostly in the aerospace industry,where weight saving is considered more critical than cost. Structurally,carbon fibers contain a blend of amorphous carbon and graphitic carbon.Their high tensile modulus results from the graphitic form, in which carbon atoms are arranged in a crystallographic structure of parallel planes or layers.The carbon atoms in each plane are arranged at the corners of interconnecting regular hexagons (Figure 2.12).The distance between the planes (3.4 A)is larger than that between the adjacent atoms in each plane (1.42 A).Strong covalent bonds exist between the carbon atoms in each plane, but the bond between the planes is due to van der Waals-type forces,which is much weaker.This results in highly anisotropic physical and mechanical prop- erties for the carbon fiber. The basal planes in graphite crystals are aligned along the fiber axis. However,in the transverse direction,the alignment can be either circumferen- tial,radial,random,or a combination of these arrangements (Figure 2.13). Depending on which of these arrangements exists,the thermoelastic properties, such as modulus(E)and coefficient of thermal expansion (a),in the radial(r) and circumferential(0)directions of the fiber can be different from those in the axial (a)or longitudinal direction.For example,if the arrangement is circumfer- ential,Ea=Ee>Er,and the fiber is said to be circumferentially orthotropic.For the radial arrangement,Ea=Er>Ee,and the fiber is radially orthotropic. When there is a random arrangement,Ea>E=Er,the fiber is transversely isotropic.In commercial fibers,a two-zone structure with circumferential 2007 by Taylor&Francis Group.LLC

higher than that of copper). The disadvantages are their low strain-to-failure, low impact resistance, and high electrical conductivity, which may cause ‘‘shorting’’ in unprotected electrical machinery. Their high cost has so far excluded them from widespread commercial applications. They are used mostly in the aerospace industry, where weight saving is considered more critical than cost. Structurally, carbon fibers contain a blend of amorphous carbon and graphitic carbon. Their high tensile modulus results from the graphitic form, in which carbon atoms are arranged in a crystallographic structure of parallel planes or layers. The carbon atoms in each plane are arranged at the corners of interconnecting regular hexagons (Figure 2.12). The distance between the planes (3.4 A˚ ) is larger than that between the adjacent atoms in each plane (1.42 A˚ ). Strong covalent bonds exist between the carbon atoms in each plane, but the bond between the planes is due to van der Waals-type forces, which is much weaker. This results in highly anisotropic physical and mechanical prop￾erties for the carbon fiber. The basal planes in graphite crystals are aligned along the fiber axis. However, in the transverse direction, the alignment can be either circumferen￾tial, radial, random, or a combination of these arrangements (Figure 2.13). Depending on which of these arrangements exists, the thermoelastic properties, such as modulus (E) and coefficient of thermal expansion (a), in the radial (r) and circumferential (u) directions of the fiber can be different from those in the axial (a) or longitudinal direction. For example, if the arrangement is circumfer￾ential, Ea¼ Eu> Er, and the fiber is said to be circumferentially orthotropic. For the radial arrangement, Ea¼ Er> Eu, and the fiber is radially orthotropic. When there is a random arrangement, Ea > Eu ¼ Er, the fiber is transversely isotropic. In commercial fibers, a two-zone structure with circumferential 1.42 Å 3.4 Å FIGURE 2.12 Arrangement of carbon atoms in a graphite crystal.
2007 by Taylor & Francis Group, LLC

(a) (b) (c) (d) (e) FIGURE 2.13 Arrangement of graphite crystals in a direction transverse to the fiber axis:(a)circumferential,(b)radial,(c)random,(d)radial-circumferential,and (e) random-circumferential. arrangement in the skin and either radial or random arrangement in the core is commonly observed [4]. Carbon fibers are manufactured from two types of precursors(starting materials),namely,textile precursors and pitch precursors.The manufacturing process from both precursors is outlined in Figure 2.14.The most common textile precursor is polyacrylonitrile(PAN).The molecular structure of PAN, illustrated schematically in Figure 2.15a,contains highly polar CN groups that are randomly arranged on either side of the chain.Filaments are wet spun from a solution of PAN and stretched at an elevated temperature during which the polymer chains are aligned in the filament direction.The stretched filaments are then heated in air at 200C-300C for a few hours.At this stage,the CN groups located on the same side of the original chain combine to form a more stable and rigid ladder structure (Figure 2.15b),and some of the CH2 groups are oxidized.In the next step,PAN filaments are carbonized by heating them at a controlled rate at 1000C-2000C in an inert atmosphere.Tension is main- tained on the filaments to prevent shrinking as well as to improve molecular orientation.With the elimination of oxygen and nitrogen atoms,the filaments now contain mostly carbon atoms,arranged in aromatic ring patterns in parallel planes.However,the carbon atoms in the neighboring planes are not yet perfectly ordered,and the filaments have a relatively low tensile modulus. As the carbonized filaments are subsequently heat-treated at or above 2000C, 2007 by Taylor Francis Group,LLC

arrangement in the skin and either radial or random arrangement in the core is commonly observed [4]. Carbon fibers are manufactured from two types of precursors (starting materials), namely, textile precursors and pitch precursors. The manufacturing process from both precursors is outlined in Figure 2.14. The most common textile precursor is polyacrylonitrile (PAN). The molecular structure of PAN, illustrated schematically in Figure 2.15a, contains highly polar CN groups that are randomly arranged on either side of the chain. Filaments are wet spun from a solution of PAN and stretched at an elevated temperature during which the polymer chains are aligned in the filament direction. The stretched filaments are then heated in air at 2008C–3008C for a few hours. At this stage, the CN groups located on the same side of the original chain combine to form a more stable and rigid ladder structure (Figure 2.15b), and some of the CH2 groups are oxidized. In the next step, PAN filaments are carbonized by heating them at a controlled rate at 10008C–20008C in an inert atmosphere. Tension is main￾tained on the filaments to prevent shrinking as well as to improve molecular orientation. With the elimination of oxygen and nitrogen atoms, the filaments now contain mostly carbon atoms, arranged in aromatic ring patterns in parallel planes. However, the carbon atoms in the neighboring planes are not yet perfectly ordered, and the filaments have a relatively low tensile modulus. As the carbonized filaments are subsequently heat-treated at or above 20008C, (a) (b) (c) (d) (e) FIGURE 2.13 Arrangement of graphite crystals in a direction transverse to the fiber axis: (a) circumferential, (b) radial, (c) random, (d) radial–circumferential, and (e) random–circumferential.
2007 by Taylor & Francis Group, LLC

Two types of precursors Polyacrylonitrile Pitch (PAN) (isotropic) Heat treatment at300°C-500℃ Wet spinning and stretching followed by heat stabilization in Mesophase pitch air at200°C-300℃for-2h (anisotropic) Melt spinning and drawing followed by heat stabilization at200°C-300°C PAN filament Pitch filament 入 Heating and stretching at 1000C-2000C in an inert atmosphere for~30 min Carbonization Relatively low-modulus (between 200 and 300 GPa), high-strength carbon fibers Heating above 2000C Graphitization with or without stretching Without stretching:relatively high-modulus (between 500 and 600 GPa)carbon fibers With stretching:carbon fibers with improved strength FIGURE 2.14 Flow diagram in carbon fiber manufacturing. their structure becomes more ordered and turns toward a true graphitic form with increasing heat treatment temperature.The graphitized filaments attain a high tensile modulus,but their tensile strength may be relatively low (Figure 2.16).Their tensile strength can be increased by hot stretching them above 2000C,during which the graphitic planes are aligned in the filament direction. Other properties of carbon fibers(e.g.,electrical conductivity,thermal conduct- ivity,longitudinal coefficient of thermal expansion,and oxidation resistance) can be improved by controlling the amount of crystallinity and eliminating the defects,such as missing carbon atoms or catalyst impurities.Tensile strength and tensile modulus are also affected by the amount of crystallinity and the presence of defects (Table 2.4). 2007 by Taylor Francis Group.LLC

their structure becomes more ordered and turns toward a true graphitic form with increasing heat treatment temperature. The graphitized filaments attain a high tensile modulus, but their tensile strength may be relatively low (Figure 2.16). Their tensile strength can be increased by hot stretching them above 20008C, during which the graphitic planes are aligned in the filament direction. Other properties of carbon fibers (e.g., electrical conductivity, thermal conduct￾ivity, longitudinal coefficient of thermal expansion, and oxidation resistance) can be improved by controlling the amount of crystallinity and eliminating the defects, such as missing carbon atoms or catalyst impurities. Tensile strength and tensile modulus are also affected by the amount of crystallinity and the presence of defects (Table 2.4). Polyacrylonitrile (PAN) Two types of precursors Pitch (isotropic) Wet spinning and stretching followed by heat stabilization in air at 2008C–3008C for ~2 h Heat treatment at 3008C–5008C PAN filament Mesophase pitch (anisotropic) Melt spinning and drawing followed by heat stabilization at 2008C–3008C Pitch filament Carbonization Heating and stretching at 10008C–20008C in an inert atmosphere for ~30 min Heating above 20008C with or without stretching Relatively low-modulus (between 200 and 300 GPa), high-strength carbon fibers Graphitization Without stretching: relatively high-modulus (between 500 and 600 GPa) carbon fibers With stretching: carbon fibers with improved strength FIGURE 2.14 Flow diagram in carbon fiber manufacturing.
2007 by Taylor & Francis Group, LLC

CN CN CH2- CH2 CH2- CH2、 CH CH CH CH CH CN CN CN (a) Heating at 220C in air CN CN C CH2 CH2 C CH CH NH Ladder structure () FIGURE 2.15 Ladder structure in an oxidized PAN molecule.(a)Molecular structure of PAN and (b)rigid ladder structure. Pitch,a by-product of petroleum refining or coal coking,is a lower cost precursor than PAN.The carbon atoms in pitch are arranged in low-molecular- weight aromatic ring patterns.Heating to temperatures above 300C polymer- izes (joins)these molecules into long,two-dimensional sheetlike structures.The highly viscous state of pitch at this stage is referred to as"mesophase."Pitch filaments are produced by melt spinning mesophase pitch through a spinneret (Figure 2.17).While passing through the spinneret die,the mesophase pitch molecules become aligned in the filament direction.The filaments are cooled to freeze the molecular orientation,and subsequently heated between 200C and 300C in an oxygen-containing atmosphere to stabilize them and make them infusible(to avoid fusing the filaments together).In the next step,the filaments are carbonized at temperatures around 2000C.The rest of the process of transforming the structure to graphitic form is similar to that followed for PAN precursors. PAN carbon fibers are generally categorized into high tensile strength(HT), high modulus (HM),and ultrahigh modulus(UHM)types.The high tensile strength PAN carbon fibers,such as T-300 and AS-4 in Table 2.1,have the 2007 by Taylor Francis Group,LLC

Pitch, a by-product of petroleum refining or coal coking, is a lower cost precursor than PAN. The carbon atoms in pitch are arranged in low-molecular￾weight aromatic ring patterns. Heating to temperatures above 3008C polymer￾izes (joins) these molecules into long, two-dimensional sheetlike structures. The highly viscous state of pitch at this stage is referred to as ‘‘mesophase.’’ Pitch filaments are produced by melt spinning mesophase pitch through a spinneret (Figure 2.17). While passing through the spinneret die, the mesophase pitch molecules become aligned in the filament direction. The filaments are cooled to freeze the molecular orientation, and subsequently heated between 2008C and 3008C in an oxygen-containing atmosphere to stabilize them and make them infusible (to avoid fusing the filaments together). In the next step, the filaments are carbonized at temperatures around 20008C. The rest of the process of transforming the structure to graphitic form is similar to that followed for PAN precursors. PAN carbon fibers are generally categorized into high tensile strength (HT), high modulus (HM), and ultrahigh modulus (UHM) types. The high tensile strength PAN carbon fibers, such as T-300 and AS-4 in Table 2.1, have the CH CH CH CH CN CN Heating at 2208C in air CH CN CH2 O O CH2 CH2 CH2 CH2 CH2 CN (a) (b) CH CH CN CH CN CH C C C CH NH C N N C CN Ladder structure FIGURE 2.15 Ladder structure in an oxidized PAN molecule. (a) Molecular structure of PAN and (b) rigid ladder structure.
2007 by Taylor & Francis Group, LLC