320 Chapter Four 30. Bergland, Lars in S.T. Peters, ed. Handbook of Composites, 2nd ed., p. 116, Chapman & Hall, London, 1998. 31. Loos, Alfred C. and Springer, George, S.J., Comp. Mater., March 17, 1983, pp. 135–169. 32. Enders, Mark L. and Hopkins, Paul C., Proc. SAMPE International Symposium and Exhibition, Vol. 36, April 1981, pp. 778–790. 33. Martin, Jeffrey D. and Sumerak, Joseph E., Composite Structures and Technology Seminar Notes, 1989, p. 542. 34. Ko, Frank K., in Engineered Materials Handbook, Vol. 1, Composites, Theodore Re- inhart, Tech. Chairman, ASM International, 1987, p. 519. 35. Hancock, P. and Cuthbertson, R.C., J. Mat Sci., 5, 762–768, 1970. 36. Kohkonen, K.E. and Potdar, N., in S.T. Peters, ed. Handbook of Composites, 2nd ed., Chapman and Hall, p. 598, London, 1998. 37. Abrate, S., in P.K. Mallick, ed., Composites Engineering Handbook, Marcel Dekker, New York, NY, 1997, p. 783. 38. Freeman, W.T. and Stein, B. A., Aerospace America, Oct. 1985, pp. 44–49. 39. Heil, C., Dittman, D., and Ishai, O., Composites (24) no. 5, 1993, pp. 447–450. 40. Chan, W.S., in P.K. Mallick, ed., Composites Engineering Handbook, Marcel Dekker, New York, NY, 1997, pp. 357–364. 41. Baker, A., P.K. Mallick, ed., Composites Engineering Handbook, Marcel Dekker, p. 747, New York, NY 1997. 42. Seidl, A.L., in Handbook of Composites, 2nd ed., S. T. Peters, ed., Chapman and Hall, London, 1999, p. 864. 43. Seidl, A.L., Repair of Composite Structures on Commercial Aircraft, 15th Annual Ad- vanced Composites Workshop, Northern California Chapter of SAMPE, 27 Jan. 1989. 44. Potter, D.L., Primary Adhesively Bonded Structure Technology (PABST) Design Handbook for Adhesive Bonding, Douglas Aircraft Co., McDonnell Douglas Corpora- tion, Long Beach, CA, Jan. 1979. 45. Nelson, W.D., Bunin, B.L., and Hart-Smith, L.J., Critical Joints in Large Composite Aircraft Structure, in Proc. 6th Conf. Fibrous Composites in Structural Design, Army Materials and Mechanics Research Center Manuscript Report AMMRC MS 83-2 (1983), pp. U-2 through II-38. 46. Baker, A., P.K. Mallick, ed., Composites Engineering Handbook, Marcel Dekker, p. 674, New York, NY, 1997. 47. Peters, S.T., Humphrey, W. D., and Foral, R., Filament Winding, Composite Structure Fabrication, 2nd ed., SAMPE Publishers, 1999, Covina, CA, pp. 9–13. 48. Kranbuehl, David E., in International Encyclopedia of Composites, Vol. 1, pp. 531–543, Stuart M. Lee, ed., VCH Publishers, New York. 49. Whitney, J.M., Daniel, I.M., and Pipes, R.B., Experimental Mechanics of Fiber Rein- forced Composite Materials, SESA Monograph No. 4, The Society for Experimental Stress Analysis, Brookfield Center, Connnecticut, 1982. 50. Carlsson, L.A. and Pipes, R.B., Experimental Characterization of Advanced Compos- ite Materials, Prentice-Hall, Englewood Cliffs, N.J., 1987. 51. Munjal, A., SAMPE Quarterly, Jan. 1986. 52. Safe Handling of Advanced Composite Materials Components, Health Association, Arlington, VA, April 1989. Composite Materials and Processes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 321 Chapter 5 Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Carl Zweben Devon, Pennsylvania 5.1 Introduction Chapter 4 discusses polymer matrix composites (PMCs) used in structural applications. This chapter covers PMCs used in thermal management and electronic packaging. It also provides an overview of metal matrix composites (MMCs), ceramic matrix composites (CMCs), and carbon matrix composites (CAMCs). The development of composite materials and the related design and manufacturing technologies is one of the most important advances in the history of materials. Composites are multifunctional materials having unprecedented mechanical and physical properties that can be tailored to meet the requirements of a particular application. Some composites also exhibit great resistance to high-temperature corrosion, oxidation, and wear. These unique characteristics provide the engineer with design opportunities not possible with conventional monolithic (unreinforced) materials. Composites technology also makes pos- sible the use of an entire class of solid materials, ceramics, in applications for which monolithic versions are unsuited because of their great strength scatter and poor resistance to mechanical and thermal shock. Furthermore, many manufacturing processes for com- posites are well adapted to the fabrication of large, complex structures. This allows consol- idation of parts, which can reduce manufacturing costs. In recent years, carbon fibers with thermal conductivities much greater than that of cop- per have been developed. These reinforcements are being used in polymer, metal, and car- bon matrices to create composites with high thermal conductivities that are being used in applications for which thermal management is important. Discontinuous versions of these fibers are also being incorporated in thermoplastic injection molding compounds, improv- ing their thermal conductivity by as much as two orders of magnitude or more. This greatly expands the range of products for which injection molded polymers can be used. Source: Handbook of Plastics, Elastomers, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 322 Chapter Five Composites are important materials that are now used widely, not only in the aerospace industry, but also in a large and increasing number of commercial applications, including ■ Internal combustion engines ■ Machine components ■ Thermal control and electronic packaging ■ Automobile, train, and aircraft structures ■ Mechanical components, such as brakes, drive shafts, and flywheels ■ Tanks and pressure vessels ■ Dimensionally stable components ■ Process industries equipment requiring resistance to high-temperature corrosion, oxida- tion, and wear ■ Offshore and onshore oil exploration and production ■ Marine structures ■ Sports and leisure equipment ■ Biomedical devices ■ Civil engineering structures The resulting increases in production volumes have helped to reduce material prices, in- creasing their attractiveness in cost-sensitive applications. It should be noted that biological structural materials occurring in nature are typically composites. Common examples are wood, bamboo, bone, teeth, and shell. Furthermore, use of artificial composite materials is not new. Bricks made from straw-reinforced mud were employed in biblical times. This material also has been widely used in the American Southwest for centuries, where it is known as adobe. In current terminology, it would be called an organic fiber-reinforced ceramic matrix composite. To put things in perspective, it is important to consider that modern composites technol- ogy is only several decades old. This is an extremely short period of time compared with other materials, such as metals, which go back millennia. In the future, improved and new materials and processes can be expected. It is also likely that new concepts will emerge, such as greater functionality, including integration of electronics, sensors, and actuators. There is no universally accepted definition of a composite material. A good description of a composite is a material consisting of two or more distinct materials bonded together. 1 This differentiates composites from materials such as alloys. Solid materials can be divided into four categories (polymers, metals, ceramics, and carbon). We consider carbon as a separate class because of its unique characteristics. We find both reinforcements and matrix materials in all four categories. This results in the po- tential for a limitless number of new material systems having unique properties that cannot be obtained with any single monolithic material. Table 5.1 shows the types of material combinations that are now in use. Composites are usually classified by the type of material used for the matrix. The four primary categories of composites are polymer matrix composites (PMCs), metal matrix composites (MMCs), ceramic matrix composites (CMCs), and carbon matrix composites (CAMCs). The last category, CAMCs, includes carbon/carbon composites (CCCs), which consist of carbon matrices reinforced with carbon fibers. For decades, CCCs were the only significant type of CAMC. However, there are now other types of composites utilizing a carbon matrix. Notable among these is silicon carbide fiber-reinforced carbon, which is being used in military aircraft gas turbine engine components. The characteristics of the four classes of matrix materials used in composites differ rad- ically. Table 5.2 presents properties of selected matrix materials from the four classes. Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Matrix Composites 323 Note that the densities, moduli, strengths, and failure strains differ greatly. These and other differences result in composite materials that have very dissimilar characteristics. Composites are now important commercial and aerospace materials. 2 At this time, PMCs are the most widely used composites. MMCs are employed in a significant and in- creasing number of commercial and aerospace applications, such as automobile engines, electronic packaging, cutting tools, circuit breaker contact pads, high-speed and precision machinery, and aircraft structures. CCCs are used in high-temperature, lightly loaded ap- plications, such as aircraft brakes, rocket nozzles, glass processing equipment, and heat treatment furnace support fixtures and insulation. Although CMCs are not as widely used at this time, there are notable applications that are indicative of their great potential. The main types of reinforcements used in composite materials include aligned continu- ous fibers, discontinuous fibers, whiskers (elongated single crystals), particles, and numer- TABLE 5.1 Types of Composite Materials Reinforcement Matrix Polymer Metal Ceramic Carbon Polymer ✔✔✔ ✔ Metal ✔✔✔ ✔ Ceramic ✔✔✔ ✔ Carbon ✔✔ ✔ TABLE 5.2 Properties of Selected Matrix Materials Material Class Density g/cm 3 (Pci) Modulus GPa (Msi) Tensile strength MPa (Ksi) Tensile failure strain (%) Thermal conductivity W/mK (Btu/hr·ft·°F) Coefficient of thermal expansion ppm/K (ppm/°F) Epoxy Polymer 1.8 (0.065) 3.5 (0.5) 70 (10) 3 0.1 (0.06) 60 (33) Aluminum (6061) Metal 2.7 (0.098) 69 (10) 300 (43) 10 180 (104) 23 (13) Titanium (6Al-4V) Metal 4.4 (0.16) 105 (15.2) 1100 (160) 10 16 (9.5) 9.5 (5.3) Silicon carbide Ceramic 2.9 (0.106) 520 (75) – <0.1 81 (47) 4.9 (2.7) Alumina Ceramic 3.9 (0.141) 380 (55) – <0.1 20 (12) 6.7 (3.7) Glass (borosilicate) Ceramic 2.2 (0.079) 63 (9) – <0.1 2 (1) 5 (3) Amorphous carbon Carbon 1.8 (0.065) 20 (3) – <0.1 5–90 (3–50) 2 (1) Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 324 Chapter Five ous forms of fibrous architectures produced by textile technology, such as fabrics and braids. 3–5 Increasingly, designers are using hybrid composites that combine different types of re- inforcements and reinforcement forms to achieve greater efficiency and reduce cost. 6,7 For example, fabrics and unidirectional tapes are often used together in structural components. In addition, carbon fibers are combined with glass or aramid to improve impact resistance. Laminates combining composites and metals, such as “Glare,” which consists of layers of aluminum and glass fiber-reinforced epoxy, are being used in aircraft structures to improve fatigue resistance. Composites are strongly heterogeneous materials. That is, the properties of a composite vary considerably from point to point in the material, depending on the material phase in which the point is located. Monolithic ceramics, metallic alloys, and intermetallic com- pounds are usually considered to be homogeneous materials, as a first approximation. Many artificial composites, especially those reinforced with fibers, are anisotropic, which means their properties vary with direction (the properties of isotropic materials are the same in every direction). This is a characteristic they share with a widely used natural fibrous composite, wood. As for wood, when structures made from artificial fi- brous composites are required to carry load in more than one direction, they are typically used in laminated form. It is worth noting that the strength properties of some metals also vary with direction. This is typically related to the manufacturing process, such as rolling. With the exception of MMCs, composites do not display plastic behavior as monolithic metals do, which makes composites more sensitive to stress concentrations. However, the absence of plastic deformation does not mean that composites should be considered brittle materials like monolithic ceramics. The heterogeneous nature of composites results in complex failure mechanisms that impart toughness. Fiber-reinforced materials have been found to produce durable, reliable structural components in countless applications. 2 For example, PMCs have been used in production boats, electrical equipment, and solid rocket motors since the 1950s, and in aircraft since the early 1970s. The technology has pro- gressed to the point where the entire empennage (tail section) of the Boeing 777 is made of carbon/epoxy. 5.2 Comparative Properties of Composite Materials There are a large and increasing number of materials that fall into each of the four types of composites, so generalization is difficult. However, as a class of materials, composites tend to have the following characteristics: ■ Tailorable mechanical and physical properties ■ High strength ■ High modulus ■ Low density ■ Excellent resistance to fatigue, creep, creep rupture, corrosion, and wear Composites are available with tailorable thermal and electrical conductivities that range from very low to very high. Composites are available with tailorable coefficients of ther- mal expansion (CTEs) ranging from –2 to + 60 ppm/K (1 to 30 ppm/°F). As for monolithic materials, each of the four classes of composites has its own particu- lar attributes. For example, CMCs tend to have particularly good resistance to corrosion, oxidation, and wear, along with high-temperature capability. Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Matrix Composites 325 There are many types of fibrous and particulate reinforcements used in composite mate- rials, including carbon, aramid, glasses, oxides, boron, and so on. 8–18 Carbon, glass, and aramid fibers are probably the most important at this time. There are dozens of different types of commercial carbon fibers. The stiffest versions have moduli of 965 GPa (140 Msi). Strengths top out at 7 GPa (1,000,000 lb/in 2 ). Carbon fibers are made from several types of precursor materials, polyacrylonitrile (PAN), petro- leum pitch, coal tar pitch, and rayon. Except for a few applications initially developed many years ago, rayon-based carbon fibers are no longer of great importance. Characteris- tics of the two types of pitch-based fibers tend to be similar but very different from those made from PAN. The key types of carbon fibers are standard modulus (SM) PAN, interme- diate modulus (IM) PAN, ultrahigh modulus (UHM) PAN, and ultrahigh modulus (UHM) pitch. The strongest UHS carbon fibers are forms of intermediate modulus (IM) fibers. Carbon fiber cost varies greatly. The least expensive industrial versions are now available for about USD 10/kg (USD 5/lb). The outstanding mechanical properties of composite materials has been a key reason for their extensive use in structures. However, composites also have important physical properties, especially low, tailorable coefficient of thermal expansion (CTE) and high ther- mal conductivity, which are key reasons for their selection in an increasing number of ap- plications. Key examples are electronic packaging and thermal management. 19–21 Many composites, such as PMCs reinforced with carbon and aramid fibers, and silicon carbide particle-reinforced aluminum, have low CTEs, which are advantageous in applica- tions requiring dimensional stability. Examples include spacecraft structures, instrument structures, and optical benches. 22 By appropriate selection of reinforcements and matrix materials, it is possible to produce composites with near-zero CTEs. Coefficient of thermal expansion tailorability provides a way to minimize thermal stresses and distortions that often arise when dissimilar materials are joined. For exam- ple, the CTE of silicon carbide particle-reinforced aluminum depends on particle con- tent. By varying the amount of reinforcement, it is possible to match the CTEs of a variety of key engineering materials, such as steel, titanium, and alumina (aluminum ox- ide). 23 The ability to tailor CTE is important in many applications. For example, titanium fit- tings are often used with carbon/epoxy (C/Ep) structures instead of aluminum, because the latter has a much larger CTE that can cause high thermal stresses under thermal cycling. Another application for which CTE is important is electronic packaging, because thermal stresses can cause failure of ceramic substrates, semiconductors, and solder joints. A unique and increasingly important property of some composites is exceptionally high thermal conductivity. This is leading to increasing use of composites in applications for which heat dissipation is a key design consideration. In addition, the low densities of com- posites make them particularly advantageous in thermal control applications for which weight is important. An important recent breakthrough is the development of injection molded PMCs with thermal conductivities as high as 100 W/m·K (58 Btu/hr·ft·°F). This is discussed in Sec. 5.5. There are a large and increasing number of thermally conductive PMCs, MMCs, and CAMCs. One of the most important types of reinforcements for these materials is pitch fi- bers. 11 PAN-based fibers have relatively low thermal conductivities. 10 However, pitch- based fibers with thermal conductivities more than twice that of copper are commercially available. These ultrahigh thermal conductivity (UHK) reinforcements also have very high stiffnesses and low densities. Fibers made by chemical vapor deposition (CVD), also called vapor-grown fibers, have reported thermal conductivities as high as 2000 W/m·K (1160 Btu/hr·ft·°F), about five times that of copper. 24 Fibers made from another form of carbon, diamond, also have the potential for thermal conductivities in this range. PMCs and CCCs reinforced with UHK carbon fibers are being used in a wide range of applica- Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 326 Chapter Five tions, including spacecraft radiators, battery sleeves, electronic packaging, and motor en- closures. Applications for specific materials are discussed later in Secs. 5.5 through 5.9. 5.3 Overview of Mechanical and Physical Properties Initially, the excellent mechanical properties of composites were the main reason for their use. 25 However, there are an increasing number of applications for which the unique and tailorable physical properties of composites are key considerations. For example, the ex- tremely high thermal conductivity and tailorable CTE of some composite material systems are leading to their increasing use in electronic packaging. Similarly, the extremely high stiffness, near-zero CTE, and low density of carbon fiber-reinforced polymers have made these composites the materials of choice in a variety of applications, including spacecraft structures, antennas, and optomechanical system components such as telescope metering structures and optical benches. Composites are complex, heterogeneous, and often anisotropic material systems. Their properties are affected by many variables, including in situ constituent properties; rein- forcement form, volume fraction, and geometry; properties of the interphase, the region where the reinforcement and matrix are joined (also called the interface); and void con- tent. The process by which the composite is made affects many of these variables. 26 Com- posites containing the same matrix material and reinforcements, when combined by different processes, may have very different properties. Several other important things must be kept in mind when considering composite prop- erties. For one, most composites are proprietary material systems made by proprietary processes. There are few industry or government specifications for composites as there are for many structural metals. However, this is also the case for many monolithic ceramics and polymers, which are widely used engineering materials. Despite their inherently pro- prietary nature, there are some widely used composite materials made by a number of manufacturers that have similar properties. Notable examples are standard modulus (SM) and intermediate modulus (IM) carbon fiber-reinforced epoxy. Another critical issue is that properties are sensitive to the test methods by which they are measured, and there are many different test methods used throughout the industry. 27,28 Furthermore, test results are very sensitive to the skill of the technician performing them. Because of these factors, it is very common to find significant differences in reported properties of what is nominally the same composite material. There is often a great deal of confusion among those unfamiliar with composites about the effect of reinforcement form. The properties of composites are very sensitive to rein- forcement form, volume fraction, and internal reinforcement geometry. It is important to keep in mind that one of the key problems with using discontinuous fiber reinforcement is that it is often difficult to control fiber orientation. For example, material flow can significantly align fibers in some regions. This affects all mechanical and physical properties, including modulus, strength, CTE, thermal conductivity, etc. For example, if there is significant flow in a region, strength properties perpendicular to the fiber direction in this area may be low. This has been a frequent source of component failures. Traditional fabric reinforcements have fibers oriented at 0 and 90°. For the sake of com- pleteness, we note that triaxial fabrics, which have fibers at 0°, +60°, and –60°, are now commercially available. Composites using a single layer of this type of reinforcement are approximately quasi-isotropic, which means that they have the same in-plane elastic (but not strength) properties in every direction. Their thermal conductivity and CTE are also approximately isotropic in the plane of the fabric. Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Matrix Composites 327 5.4 Manufacturing Considerations Composites also offer a number of significant manufacturing advantages over monolithic metals and ceramics. For example, fiber-reinforced polymers and ceramics can be fabri- cated in large, complex shapes that would be difficult or impossible to make with other materials. 26,29–31 The ability to fabricate complex shapes allows consolidation of parts, which reduces machining and assembly costs. Some processes allow fabrication of parts in their final shape (net shape) or close to their final shape (near-net shape), which also produces manufacturing cost savings. The relative ease with which smooth shapes can be made is a significant factor in the use of composites in boats, aircraft, and other applica- tions for which aerodynamic considerations are important. Manufacturing considerations for each of the four classes of composites are discussed in the following sections, along with their properties. 5.5 Polymer Matrix Composites Chapter 4 presents a thorough discussion of polymer matrix composites focused primarily on structural applications. This chapter emphasizes physical properties, but mechanical properties are presented for completeness. The high thermal conductivities of some PMCs has led to their increasing use in appli- cations like spacecraft structures and electronic packaging components, e.g., printed circuit board heat sinks, heat spreaders, and heat sinks used to cool microprocessors. The addition of thermally conductive carbon fibers and ceramic particles to thermoplastics has opened the door to use of injection molded parts for which plastics previously could not be used because of their low thermal conductivities. We consider some examples in this section. There are important issues that must be discussed before presenting composite proper- ties. The traditional structural materials are primarily metal alloys for most of which there are industry and government standards. The situation is very different for composites. Most reinforcements and matrices are proprietary materials for which there are no stan- dards. In addition, many processes are proprietary. This is similar to the current situation for most polymers and ceramics. The matter is further complicated by the fact that there are many test methods in use to measure mechanical and physical properties. 27,28 As a re- sult, there are often conflicting material property data in the usual sources used by engi- neers, published papers, and manufacturers’ literature. The data presented in this chapter represent a carefully evaluated distillation of information from many sources. However, in view of the uncertainties discussed, the properties presented in this chapter should be con- sidered approximate values. Polymers are relatively weak, low-stiffness materials with low thermal conductivities and high coefficients of thermal expansion. To obtain materials with mechanical properties that are acceptable for structural applications, it is necessary to reinforce them with contin- uous or discontinuous fibers. The addition of ceramic or metallic particles to polymers re- sults in materials that have increased modulus. As a rule, strength typically does not increase significantly and may actually decrease. However, there are many particle-rein- forced polymers used in electronic packaging, primarily because of their physical proper- ties. For these applications, ceramic particles such as alumina, aluminum nitride, boron nitride, and even diamond are added to obtain an electrically insulating material with higher thermal conductivity and lower CTE than the monolithic base polymer. Metallic particles such as silver and aluminum are added to create materials that are both electri- cally and thermally conductive. These materials have replaced lead-based solders in some applications. There are also magnetic composites made by incorporating ferrous or perma- nent magnet particles in various polymers. A common example is magnetic tape used to record audio and video. Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 328 Chapter Five Polymer matrices generally are relatively weak, low-stiffness, viscoelastic materials. They also have very low thermal and electrical conductivities. The strength and stiffness of PMCs come primarily from the fiber phase. In a vacuum, resins outgas water and organic and inorganic chemicals, which can con- dense on surfaces with which they come in contact. This can be a problem in optical sys- tems and electronic packaging. Outgassing can result in corrosion and affect surface properties critical for thermal control, such as absorptivity and emissivity. Outgassing can be controlled by resin selection and baking out the component, followed by storage in a dry environment. For a wide range of applications, composites reinforced with continuous fibers are the most efficient structural materials at low to moderate temperatures. Consequently, we fo- cus on them. Table 5.3 presents room-temperature mechanical properties of unidirectional polymer matrix composites reinforced with key fibers: E-glass, aramid, boron, standard modulus (SM) PAN (polyacrylonitrile) carbon, intermediate modulus (IM) PAN carbon, ultrahigh modulus (UHM) PAN carbon, ultrahigh modulus (UHM) pitch carbon, and ul- trahigh thermal conductivity (UHK) pitch carbon. The fiber volume fraction is 60 percent, a typical value. The properties presented in Table 5.3 are representative of what can be obtained at room temperature with a well made PMC employing an epoxy matrix. Epoxies are widely used, provide good mechanical properties, and can be considered a reference matrix mate- rial. Properties of composites using other resins may differ from these. This has to be ex- amined on a case-by-case basis. The properties of PMCs, especially strengths, depend strongly on temperature. The temperature dependence of polymer properties differs considerably. This is also true for different epoxy formulations, which have different cure and glass transition temperatures. The properties shown in Table 5.3 are axial, transverse and shear moduli, Poisson’s ra- tio, tensile and compressive strengths in the axial and transverse directions, and in-plane shear strength. The Poisson’s ratio presented is called the major Poisson’s ratio. It is de- fined as the ratio of the magnitude of transverse strain divided by the magnitude of axial strain when the composite is loaded in the axial direction. Note that transverse moduli and strengths are much lower than corresponding axial values. Carbon fibers display nonlinear stress-strain behavior. Their moduli increase under in- creasing tensile stress and decrease under increasing compressive stress. This makes the method of calculating modulus critical. Various tangent and secant definitions are used throughout the industry, contributing to the confusion in reported properties. For example, on one program, it was found that the fiber supplier, prepreg supplier, and end user were all using different definitions of modulus, resulting in significantly different values. The moduli presented in Table 5.3 are based on tangents to the stress-strain curves at the origin. Using this definition, tensile and compressive moduli are usually very similar. However, this is not the case for moduli computed using various secants. These typically produce compression moduli that are significantly lower than tensile moduli, because the stress-strain curves are nonlinear. As a result of the low transverse strengths of unidirectional laminates, they are rarely used in structural applications. The design engineer selects laminates with layers in several directions to meet requirements for strength, stiffness, buckling, etc. There are an infinite number of laminate geometries that can be selected. For comparative purposes, it is useful to consider quasi-isotropic laminates, which have the same elastic properties in all direc- tions in the plane. Laminates have quasi-isotropic elastic properties when they have the same percentage of layers every 180/n degrees, where n ≥ 3. The most common quasi-isotropic laminates have layers that repeat every 60°, 45°, or 30°. We note, however, that strength properties in the plane are not isotropic for these laminates, although they tend to become more uniform Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 329 TABLE 5.3 Representative Mechanical Properties of Selected Unidir ectional Polymer Matrix Composites, Nominal Fiber Volume Fraction = 60 Percent Fiber Axial modulus GPa (Msi) Transverse modulus GPa (Msi) In-plane shear modulus GPa (Msi) Poisson’s ratio Axial tensile strength MPa (Msi) Transverse tensile strength MPa (Msi) Axial compressive strength MPa (Msi) Transverse compressive strength MPa (Msi) In-plane shear strength MPa (Msi) E-glass 45 (6.5) 12 (1.8) 5.5 (0.8) 0.28 1020 (150) 40 (7) 620 (90) 140 (20) 70 (10) Aramid 76 (11) 5.5 (0.8) 2.1 (0.3) 0.34 1240 (180) 30 (4.3) 280 (40) 140 (20) 60 (9) Boron 210 (30) 19 (2.7) 4.8 (0.7) 0.25 1240 (180) 70 (10) 3310 (480) 280 (40) 90 (13) Standard modulus carbon (PAN) 145 (21) 10 (1.5) 4.1 (0.6) 0.25 1520 (220) 41 (6) 1380 (200) 170 (25) 80 (12) Ultrahigh modulus carbon (PAN) 310 (45) 9 (1.3) 4.1 (0.6) 0.20 1380 (200) 41 (6) 760 (110) 170 (25) 80 (12) Ultrahigh modulus carbon (pitch) 480 (70) 9 (1.3) 4.1 (0.6) 0.25 900 (130) 20 (3) 280 (40) 100 (15) 41 (6) Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. [...]... June/July 199 8 23.K Schmidt and C Zweben, Mechanical and Thermal Properties of Silicon Carbide Particle-Reinforced Aluminum, Thermal and Mechanical Behavior of Metal Matrix and Ceramic Matrix Composites, ASTM STP 1080, L M Kennedy, H.H Moeller and W S Johnson, Eds., American Society for Testing and Materials, Philadelphia, 198 9 24.D D L Chung and C Zweben, Composites for Electronic Packaging and Thermal... the most important of the newer types of MMCs The low cost of the aluminum matrix and silicon carbide particle makes these composites of particular interest There are wide ranges of materials falling in this category They are made by a variety of processes, which are discussed later in this section Properties depend on the type of particle, particle volume fraction, matrix alloy, and the process used... The transverse CTEs of the composites are all positive, and their magnitudes are much larger than the magnitudes of the corresponding axial CTEs This results from the high CTE of the matrix and a Poisson effect caused by constraint of the matrix in the axial direction and lack of constraint in the transverse direction The transverse CTE of aramid composites is particularly high, in part because the fibers... Zweben, Thermal Management and Electronic Packaging Applications, ASM Handbook, Vol 21, Composites, ASM International, Materials Park, Ohio, 2002 39. C Zweben, Metal Matrix Composites: Aerospace Applications, Encyclopedia of Advanced Materials, M.C Flemings, et al., Eds., Pergamon Press, Oxford 199 4 40.R Warren, Ed., Ceramic-Matrix Composites, Chapman and Hall, New York, 199 2 41.Advanced Materials by... Structural Composites, Advanced Topics in Materials Science and Engineering, J I Moran-Lopez and J M Sanchez, Eds., Plenum Press, New York, 199 3 4 W S Smith and Carl Zweben, Properties of Constituent Materials, Section 2, Engineered Materials Handbook, Vol 1, Composites, ASM International, Materials Park, Ohio, 198 7, pp 43–104 5 Comprehensive Composite Materials, Vol 1: Fiber Reinforcements and General... ( 59) 410 ( 59) 205 (30) 73 (11) 73 (11) 580 (84) 580 (84) 270 ( 39) 96 (14) 96 (14) 65 (9. 4) 250 (37) In-plane Shear Strength MPa (Ksi) 1100 (160) 190 (28) 330 (48) Transverse compressive strength MPa (Ksi) Mechanical Properties of Selected Quasi-isotropic Polymer Matrix Composites, Fiber Volume Fraction = 60 Percent Fiber TABLE 5.4 Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, ...Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites 330 Chapter Five as the angle of repetition becomes smaller Laminates have quasi-isotropic CTE and coefficient of expansion when they have the same percentage of layers in every 180/m degrees, where m ≥ 2 For example, laminates with equal numbers of layers at 0° and 90 ° have quasi-isotropic... Companies All rights reserved Any use is subject to the Terms of Use as given at the website Source: Handbook of Plastics, Elastomers, and Composites Chapter 6 Plastics in Coatings and Finishes Carl P Izzo Industrial Paint Consultant Export, Pennsylvania 6.1 Introduction Coatings and finishes are composed of film-forming resins, pigments, solvents, and additives.1 Although their existence predates plastics... for 3D composites High cost of many systems The variables affecting properties include type of fiber, reinforcement form, geometry, and volume fraction and matrix characteristics Because of the low interlaminar strength properties of CCCs, many applications, particularly those with thick walls, often use three-dimensional reinforcement As mentioned earlier, one of the most significant limitations of CCCs... to the Terms of Use as given at the website Metal Matrix Composites, Ceramic Matrix Composites, Carbon Matrix Composites, and Thermally Conductive Polymer Matrix Composites 340 Chapter Five 5.8 Ceramic Matrix Composites Ceramic matrix composites (CMCs) can be thought of as an improved form of carbon matrix composite in which the carbon matrix is replaced with ceramics that are stronger and much more . Mallick, ed., Composites Engineering Handbook, Marcel Dekker, p. 747, New York, NY 199 7. 42. Seidl, A.L., in Handbook of Composites, 2nd ed., S. T. Peters, ed., Chapman and Hall, London, 199 9, p. 864. 43 Hancock, P. and Cuthbertson, R.C., J. Mat Sci., 5, 762–768, 197 0. 36. Kohkonen, K.E. and Potdar, N., in S.T. Peters, ed. Handbook of Composites, 2nd ed., Chapman and Hall, p. 598 , London, 199 8. 37 ed., Composites Engineering Handbook, Marcel Dekker, New York, NY, 199 7, p. 783. 38. Freeman, W.T. and Stein, B. A., Aerospace America, Oct. 198 5, pp. 44– 49. 39. Heil, C., Dittman, D., and Ishai,