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Polymer III

Molecular Motions. Vibration of atoms about equilibriumMotion of a few atoms or rotation/vibration of side groupsCooperative movement of segments (40-50 atoms long).Translational motion of entire molecules. . Deformation . Two Processes in ThermoplasticsCrazing (amorphous)b. Shear Yielding or

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Polymer III

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    1. Polymer III Polymer Failure & Environmental Effects

    2. Molecular Motions Vibration of atoms about equilibrium Motion of a few atoms or rotation/vibration of side groups Cooperative movement of segments (40-50 atoms long). Translational motion of entire molecules.

    3. Deformation Two Processes in Thermoplastics Crazing (amorphous) b. Shear Yielding or Shear Flow

    4. Deformation Processes Crazing Amorphous Volume increase Extremely small Solvents assist

    6. Deformation Process Shear Yielding or Shear Flow Shear stress induced Translation of molecules Largely irreversible Absorbs lots of energy

    7. Shear Yielding in Semicrystalline Semicrystalline yield is not reversible Further yield is possible in which remaining crystallites also break up.

    8. Molecular Orientation Failure process depends on molecular orientation Generally more orientation = greater toughness

    9. Fracture in Polymers Polymers will undergo slow stable crack growth (ie. Kappl<K1C) Fracture process zone dominated by either crazing or shear yielding. Surface morphology can be complex

    10. Fracture Process Zone: PE

    12. Crack Tip in Polycarbonate Very tough amorphous polymer Shear yield dominates Shear Bands ahead of crack tip

    17. Toughness in Polymers Toughness enhanced by improved molecular mobility (plasticizers, temperature, free volume, lower crystallinity) Second phase toughening common (rubber, TP in TS) Most fillers reduce toughness

    23. Moisture Absorption in Delrin

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