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Unformatted text preview: 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, Cal ister 7e . Chapter 15 - 3 Tensile Response: Brittle & Plastic brittle failure plastic failure (MPa) x x crystal ine regions slide fibrillar structure near failure crystal ine regions align onset of necking Initial Near Failure semi- crystal ine case aligned, cross- linked case networked case amorphous regions elongate unload/reload Stress-strain curves adapted from Fig. 15.1, Cal ister 7e. Inset figures along plastic response curve adapted from Figs. 15.12 & 15.13, Cal ister 7e . (Figs. 15.12 & 15.13 are from J.M. Schultz, Polymer Materials Science , Prentice- Hal , 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, Cal ister 7e . (Fig. 15.13 is from J.M. Schultz, Polymer Materials Science , Prentice-Hal , 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, Cal ister 7e. Inset figures along elastom er curve (green) adapted from Fig. 15.15, from Fig....
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- Spring '08