lec5 - Elements of Polymer Structure and Viscoelasticity...

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Unformatted text preview: Elements of Polymer Structure and Viscoelasticity David M. Parks Mechanics and Materials II 2.002 February 18, 2004 Outline Elements of polymer structure Linear vs. branched; Vinyl polymers and substitutions Packing of polymer chains Random/amorphous Glass transition temperature, T G Semi-crystalline Crystalline volume fraction; melting temperature Amorphous T G Elements of linear viscoelasticity Creep and relaxation Analogue models Idealized Linear Elastic Response Linear elasticity : [NO] Creep [NO] Relaxation INPUT: INPUT: OUTPUT: OUTPUT: Note: units of E are stress. Idealized Linear Viscous Response Linear viscosity : Creep: Relaxation: INPUT: Note: units of are stress time becomes arbitrarily large during e.g., sec MPa an infinitesimal time interval, and then, like the strain-rate, goes to zero INPUT: OUTPUT: OUTPUT: The strain rate (and therefore stress) Maxwell Model: an Idealized Linear Viscoelastic Response Creep: INPUT: UTPUT: For times near the finite stress jump, all strain occurs in the elastic element; During the hold period, all strain occurs in the viscous element Maxwell Model: an Idealized Linear...
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lec5 - Elements of Polymer Structure and Viscoelasticity...

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