Week14Ch15

Week14Ch15 - Chapter 15: Characteristics, Applications...

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Chapter 15: haracteristics Applications & Characteristics, Applications & Processing of Polymers ISSUES TO ADDRESS. .. What are the tensile properties of polymers and how What are the tensile properties of polymers and how are they affected by basic microstructural features ? • Hardening, anisotropy, and annealing in polymers Hardening, anisotropy, and annealing in polymers . How does the elevated temperature mechanical sponse of polymers compare to ceramics and metals? response of polymers compare to ceramics and metals? What are the primary polymer processing methods? Chapter 15 - 1
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Mechanical Properties • i.e. stress-strain behavior of polymers brittle polymer TS of polymer ca. 10% that of metals plastic elastomer elastic modulus – less than metal Strains – deformations > 1000% possible Adapted from Fig. 15.1, Callister 7e . Chapter 15 - 2 (for metals, maximum strain ca. 10% or less)
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Temperature influence p Chapter 15 - Strain rate influence: slow => High T
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Elastic behavior ( ) ε σ E = Viscoelastic behavior asing T Incre a Viscous behavior Chapter 15 - f15 05 pg528
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Viscoelastic relaxation modulus 0 ) ( ) ( ε σ t t E r = 0 strain constant Creep modulus 0 ) ( ) ( t t E c = p Chapter 15 - f15_06_pg529 0 stress constant
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A: highly crystallized B: Rubber or elastomeric C: amorphous Chapter 15 -
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Polymer Fracture Crazing – spherulites plastically deform to fibrillar structure alligned chains – microvoids and fibrillar bridges form fibrillar bridges microvoids crack Adapted from Fig. 15.9, Callister 7e . Chapter 15 - 7
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Tensile Response: Brittle & Plastic Pa) fibrillar ear Failure brittle failure lastic failure σ (MPa) x structure near failure onset of ecking Near Failure plastic failure x necking Initial ε unload/reload crystalline regions slide aligned, cross- linked case networked case semi- crystalline case amorphous regions elongate crystalline regions align Chapter 15 - 8
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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
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Week14Ch15 - Chapter 15: Characteristics, Applications...

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