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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 fabricated in large, complex shapes that would be difficult or impossible to make with other materials.
The ability to fabricate complex shapes allows consolidation of parts, which reduces machining and assembly costs. Some processes allow fabrication of parts to 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 aircraft and other applications for which aerodynamic considerations are important.




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  • Carl Zweben
    Devon, Pennsylvania


    Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
    Edited by Myer Kutz
    Copyright  2006 by John Wiley & Sons, Inc.



    for STEP BY STEP GUIDE unigraphics simple tutorial please visit.........
    www.unigraphicsimpletutorial.blogspot.com

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  • www.unigraphic-simple-tutorial.com




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    Comparative Properties of Composite Materials

    There are a large and increasing number of materials that fall in each of the four types of composites, making generalization difficult. However, as a class of materials, composites tend to have the following characteristics: high strength; high modulus; low density; excellent resistance to fatigue, creep, creep rupture,  corrosion, and wear; and low coefficient of thermal expansion (CTE). As for monolithic materials, each of the four classes of composites has its own particular attributes. For example, CMCs tend to have particularly good resistance to corrosion, oxidation, and wear, along with high-temperature capability. 
    For applications in which both mechanical properties and low weight are important,
    useful figures of merit are specific strength (strength divided by specific gravity or density) and specific stiffness (stiffness divided by specific gravity or density). Figure 2 presents specific stiffness and specific tensile strength of conventional structural metals (steel, titanium, aluminum, magnesium, and beryllium), two engineering ceramics (silicon nitride and alumina), and selected composite materials. The composites are PMCs reinforced with selected continuous fibers—carbon, aramid, E-glass, and boron—and an MMC, aluminum containing silicon carbide particles. Also shown is beryllium–aluminum, which can be considered a type of metal matrix composite, rather than an alloy, because the mutual solubility of the constituents at room temperature is low.
    The carbon fibers represented in Fig. 2 are made from several types of precursor materials: 
    polyacrylonitrile (PAN), petroleum pitch, and coal tar pitch. Characteristics of the
    two types of pitch-based fibers tend to be similar but very different from those made from
    PAN. Several types of carbon fibers are represented: standard-modulus (SM) PAN, ultrahighstrength
    (UHS) PAN, ultrahigh-modulus (UHM) PAN, and UHM pitch. These fibers are
    discussed in Section 2. It should be noted that there are dozens of different kinds of commercial
    carbon fibers, and new ones are continually being developed.
    Because the properties of fiber-reinforced composites depend strongly on fiber orientation,
    fiber-reinforced polymers are represented by lines. The upper end corresponds to the
    axial properties of a unidirectional laminate, in which all the fibers are aligned in one direction.
    The lower end represents a quasi-isotropic laminate having equal stiffness and approximately
    equal strength characteristics in all directions in the plane of the fibers.
    As Figure 2 shows, composites offer order-of-magnitude improvements over metals in
    both specific strength and stiffness. It has been observed that order-of-magnitude improvements
    in key properties typically produce revolutionary effects in a technology. Consequently,
    it is not surprising that composites are having such a dramatic influence in engineering
    applications.



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  • Carl Zweben
    Devon, Pennsylvania


    Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
    Edited by Myer Kutz
    Copyright  2006 by John Wiley & Sons, Inc.



    for STEP BY STEP GUIDE unigraphics simple tutorial please visit.........
    www.unigraphicsimpletutorial.blogspot.com

    ---or---


  • www.unigraphic-simple-tutorial.com








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    Classes and Characteristics of Composite Materials

    There is no universally accepted definition of a composite material. For the purpose of this work, we consider a composite to be a material consisting of two or more distinct phases, bonded together.1
    Solid materials can be divided into four categories: polymers, metals, ceramics, and carbon, which we consider as a separate class because of its unique characteristics. We find both reinforcements and matrix materials in all four categories. This gives us the ability to create a limitless number of new material systems with unique properties that cannot be
    obtained with any single monolithic material. Table 1 shows the types of material combinations 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/carbon composites (CCCs). At this time, PMCs are the most widely used class of composites. However, there are important applications of the other types, which are indicative of their great potential in mechanical engineering applications.
    Figure 1 shows the main types of reinforcements used in composite materials: aligned continuous fibers, discontinuous fibers, whiskers (elongated single crystals), particles, and numerous forms of fibrous architectures produced by textile technology, such as fabrics and braids. Increasingly, designers are using hybrid composites that combine different types of  reinforcements to achieve more efficiency and to reduce cost. A common way to represent fiber-reinforced composites is to show the fiber and matrix separated by a slash. For example, carbon fiber-reinforced epoxy is typically written ‘‘carbon/ epoxy,’’ or, ‘‘C/Ep.’’ We represent particle reinforcements by enclosing them in parentheses followed by ‘‘p’’; thus, silicon carbide (SiC) particle-reinforced aluminum appears as ‘‘(SiC)p/ Al.’’
    Composites are strongly heterogeneous materials; that is, the properties of a composite vary considerably from point to point in the material, depending on which material phase the point is located in. Monolithic ceramics and metallic alloys are usually considered to be homogeneous materials, to 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 fibrous composites are required to carry load in more than one direction, they are used in laminated form.
    Many fiber-reinforced composites, especially PMCs, MMCs, and CCCs, do not display plastic behavior as metals do, which makes them more sensitive to stress concentrations. However, the absence of plastic deformation does not mean that composites are 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. The unique characteristics of composite materials, especially anisotropy, require the use of special design methods.




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  • Carl Zweben
    Devon, Pennsylvania


    Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
    Edited by Myer Kutz
    Copyright  2006 by John Wiley & Sons, Inc.




    for STEP BY STEP GUIDE solidwork simple tutorial please visit.........
    www.solidworksimpletutorial.blogspot.com

    ---or---


  • www.solidwork-simple-tutorial.com
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