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MSE_2610_HW_3_solutions

MSE_2610_HW_3_solutions - MSE 2610 Introduction to the...

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MSE 2610 Introduction to the Mechanical Properties of Materials Fall 2008 Homework Assignment #3 Due: 26 September 2008 1.) The modulus of a lightly cross-linked elastomer is plotted against temperature. Temperature (K) Modulus (MPa) A B C D For each area A-D, explain how the polymer chains interact with one another and result in the relative modulus shown in the graph. a.) Glassy regime : The polymer chain uncoiling time is very long compared to the test time. The chains are “locked-in” to a particular confirmation, and there is insufficient thermal energy to allow large-scale motion of the polymer chains. Elasticity is due almost entirely to bond stretching. b.) Glass Transition : The polymer chain uncoiling time is on the order of the test time. There is sufficient thermal energy for some chain sliding. Both bond stretching and chain uncoiling contribute to elasticity. c.) Entropic Elasticity : The polymer chain uncoiling time is short compared to the test time. The chains seek the lowest free energy by maximizing disorder in the chains. The material becomes stiffer with temperature because fully uncoiled polymer chains have a high degree of order. d.) Viscous Flow/Degradation : In the regime, the bonds between polymer chains completely break down, resulting viscous flow or polymer degradation. The polymer loses mechanical stability and elasticity. 2.)
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MSE_2610_HW_3_solutions - MSE 2610 Introduction to the...

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