Polymer viscoelasticity part 1/2

>> Saturday, 13 September 2008

There will be screenshots from Rheological Behavior of Fluids movie applied, it is available from Massachusetts Institute of Technology web page, Realplayer is an requirement.
The movie is s great introduction for no-newtonian fluids (as polymers are) properties. There are many experiments which will be key for polymer processing understanding where this properties emerge. The movie history reaches latest 60th (fundaments for fluid mechanics and rheology are the same) it is not short more than 22 minutes but it is worth seeing more than once. As you listen carefully you will find answers for problems from: newtonian fluids, no-newtonian fluids (Bingham, pseudoplastic, dilatant fluids), viscoelasticity effects, Weissenberg effect, Barus effect, time dependent effects
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, resist shear flow and stain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just as quickly return to their original state once the stress is removed. Viscosity we know already. Elasticity is material return ability to their original state once the stress is removed.

Polymers have both solid and fluid properties and are time dependent (because of its molecular structure). Viscoelasticity gauge in polymer processing is relation between characteristic material time and characteristic process time defined as Deborah number.

Back to the movie, the first example shows how time scale is important, ball (viscoelastic material, why, find below) for very short time, process time behaves as elastic solid (Deborah number tends to infinity).

For long time, process time ball behaves as viscous fluid ( Deborah number tends to zero).

In part 2/2 there will be about viscoelasticity effects, that is Weissenberg effect and Barus effect.

Once more, technical issue, from Massachusetts Institute of Technology web page click right on Rheological Behavior of Fluids than save target as on your drive, and run using Realplayer

1 komentarze:

Anonymous,  17 January 2011 at 01:20  

Il semble que vous soyez un expert dans ce domaine, vos remarques sont tres interessantes, merci.

- Daniel

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