EmaCh15 - Chapter 15 Characteristics Applications...

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5/1/2008 1 Chapter 15 - 1 ISSUES TO ADDRESS... What are the tensile properties of polymers and how are they affected by basic microstructural features ? Hardening, anisotropy, and annealing in polymers . How does the elevated temperature mechanical response of polymers compare to ceramics and metals? Chapter 15: Characteristics, Applications & Processing of Polymers What are the primary polymer processing methods? Chapter 15 - 2 Mechanical Properties i.e. stress-strain behavior of polymers brittle polymer plastic elastomer FS of polymer ca. 10% that of metals Strains deformations > 1000% possible (for metals, maximum strain ca. 10% or less) elastic modulus less than metal Adapted from Fig. 15.1, Callister 7e . Chapter 15 - 3 Tensile Response: Brittle & Plastic brittle failure plastic failure (MPa) x x crystalline regions slide fibrillar structure near failure crystalline regions align onset of necking Initial Near Failure semi- crystalline case aligned, cross- linked case networked case amorphous regions elongate unload/reload Stress-strain curves adapted from Fig. 15.1, Callister 7e. Inset figures along plastic response curve adapted from Figs. 15.12 & 15.13, Callister 7e . (Figs. 15.12 & 15.13 are from J.M. Schultz, Polymer Materials Science , Prentice- Hall, Inc., 1974, pp. 500-501.) Chapter 15 - 4 Predeformation by Drawing Drawing …(ex: monofilament fishline) -- stretches the polymer prior to use -- aligns chains in the stretching direction Results of drawing: -- increases the elastic modulus ( E ) in the stretching direction -- increases the tensile strength ( TS ) in the stretching direction -- decreases ductility (% EL ) Annealing after drawing... -- decreases alignment -- reverses effects of drawing. Compare to cold working in metals! Adapted from Fig. 15.13, Callister 7e . (Fig. 15.13 is from J.M. Schultz, Polymer Materials Science , Prentice-Hall, Inc., 1974, pp. 500-501.) Chapter 15 - 5 Compare to responses of other polymers: -- brittle response (aligned, crosslinked & networked polymer) -- plastic response (semi-crystalline polymers) Stress-strain curves adapted from Fig. 15.1, Callister 7e. Inset figures along elastomer curve (green) adapted from Fig. 15.15, Callister 7e . (Fig. 15.15 is from Z.D. Jastrzebski,
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