L20_Polymer_Properties_Annotated(2)

This phenomenon is demonstrated in figure 155d for

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Unformatted text preview: d. For the What Effects a TP behavior, the imposition of a stress in the man intermediate viscoelastic Properties? 2. Temperature - 15.5a results in an instantaneous elastic strain, which is followed by ner of Figure (c) TPviscous, time-dependent strain, a form of anelasticity (Section 6.4); this behavior Polymers display viscoelastic properties illustrated in like a fluid . viscous – Figure 15.5c A familiar a elastic – likeexample of these viscoelastic extremes is found in a silicone poly rubber mer that is sold as a novelty and known by some as “Silly Putty.” When rolled int Lecture 20-21 Load Strain Elastic Response elastic recovery ta Time ta Strain Viscous (c) elastic deformation no recovery Slow viscous deformation elastic deformation tr tr Viscous Response Recovery Time Time (b) Viscoelastic Response ta TP tr (a) Strain ure 15.5 d versus ere load applied ously at released . For the cycle in -versusnses are y elastic coelastic viscous haviors. ta Time (d) tr 11 MSE 230 - Trice Lecture 20-21 More on Viscoelasticity – Relaxation Modulus Time dependent Elastic modulus stress constant In this test: • Specimen is strained rapidly in tension to a predetermined low strain • The stress necessary to maintain this strain is measured as a function of time dependent - Time ________________ elastic modulus - As increase temperature, σ(t) relaxes faster and therefore the elastic modulus, decreases E, _______________ TP Lecture 20-21 More on Viscoelasticity – Relaxation Modulus 5 Regions of Viscoelastic Behavior 1.Glassy: T<Tg polymer is brittle 2. Leathery: Tg glass transition region, drop in E over a 10 to 30 °C 3. Rubbery: T>Tg - Equal balance between viscous and elastic behavior 4. Rubbery Flow: - Increased viscous behavior silly putty is in this region 5. Viscous Flow: - Flowable, no elastic contribution 13 TP...
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