ch14 - 10/3/2010 Chapter 14: Fabrication of Plastics,...

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10/3/2010 1 Chapter 14: Fabrication of Plastics, Ceramics, and Composites 14.1 Introduction Plastics, ceramics, and composites have different structure and properties than metals Principles of material selection and manufacturing are different Large, complex shapes can be formed as a single unit Processes can produce a near perfect shape and surface product
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10/3/2010 2 14.2 Fabrication of Plastics A successful plastic product is manufactured so that it satisfies the various mechanical and physical property requirements The preferred manufacturing method is determined by the desired size, shape, and quantity There are three main different types of polymers: thermoplastics, thermosets, and elastomers Polymer Structure FIGURE 10.1 Basic structure of some polymer molecules: (a) ethylene molecule; (b) polyethylene, a linear chain of many ethylene molecules; (c) molecular structure of various polymers. These molecules are examples of the basic building blocks for plastics.
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10/3/2010 3 Effect of Molecular Weight FIGURE 10.2 Effect of molecular weight and degree of polymerization on the strength and viscosity of polymers. Polymer Chains FIGURE 10.3 Schematic illustration of polymer chains. (a) Linear structure; thermoplastics such as acrylics, nylons, polyethylene, and polyvinyl chloride have linear structures. (b) Branched structure, such as polyethylene. (c) Cross-linked structure; many rubbers and elastomers have this structure. Vulcanization of rubber produces this structure. (d) Network structure, which is basically highly cross- linked; examples include thermosetting plastics such as epoxies and phenolics.
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10/3/2010 4 Effect of Temperature FIGURE 10.4 Behavior of polymers as a function of temperature and (a) degree of crystallinity and (b) cross-linking. The combined elastic and viscous behavior of polymers is known as viscoelasticity. Crystallinity FIGURE 10.5 Amorphous and crystalline regions in a polymer. Note that the crystalline region (crystallite) has an orderly arrangement of molecules. The higher the crystallinity, the harder, stiffer, and less ductile is the polymer.
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10/3/2010 5 Glass-Transition Temperature FIGURE 10.6 Specific volume of polymers as a function of temperature. Amorphous polymers, such as acrylic and polycarbonate, have a glass-transition temperature, T g , but do not have a specific melting point, T m . Partly crystalline polymers, such as polyethylene and nylons, contract sharply at their melting points during cooling. TABLE 10.2 Glass-Transition and Melting Temperatures of Selected Polymers Deformation of Polymers FIGURE 10.7 Various deformation modes for polymers.: (a) elastic; (b) viscous; (c) viscoelastic (Maxwell model); and (d) viscoelastic (Voigt or Kelvin model). In all cases, an instantaneously applied load occurs at time t o , resulting in the strain paths shown. FIGURE 10.8
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This note was uploaded on 02/22/2012 for the course IE 370 taught by Professor Chunghorng,r during the Spring '08 term at Purdue University.

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ch14 - 10/3/2010 Chapter 14: Fabrication of Plastics,...

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