Elongational (= Extensional) Viscosity

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Posted by(작성하신 분) rex ( August 08, 2000 at 14:28:33: )

In Reply to(원문) : 점도의 종류와 점도계에 대해 질문드립니다.
posted by(원문 작성자) : 류근영 on July 26, 2000 at 00:18:01:

: 저는 점도의 종류가 절대점도와 동점도로만 구분되는지 알았는데, 얼마전에 normal, extentional, elonggational viscosity라고 분류되기도 한다고들었습니다. 이것들에 대해서는 다른 참고자료에서 찾아보기힘든대요. 혹시 아시는 것이 있으면 설명좀 부탁드립니다.
================================

All you ask is rhological terminologies.
EXTENSIONAL (= ELONGATIONAL) viscosity,
NORMAL Stresses, ELASTICITY etc..

I suggest you to refer some of Polymeric , Rheology text books as follows,
(1) Polymer Processing and Structure Development
by Arthur N. Wilkinson, Anthony J. Ryan
Paperback - 304 pages (April 1999)
Kluwer Academic Pub; ISBN: 0751403636

(2) Polymer Processing fundamentals
Tim A Osswald
ISBN US: 1-56990-262-3
Published: 1998
Edition: Softbound 192 pages
Hanser Gardner

------------------------------------
Source : http://www.polydynamics.com/fra_glossary.htm

ELONGATIONAL VISCOSITY ( = EXTENSIONAL VISCOSITY) :

The resistance to extension (while the (common) viscosity term describes the resistance to shearing). For Newtonian fluids the elongational viscosity is equal to 3x viscosity (3 is known as the Trouton Ratio).

Polymers are non-Newtonian and the elongational viscosity is usually between 3x viscosity and 100x viscosity. Melt strength is just a rough engineering measure of the elongational viscosity, determined from the force required to break an extruded strand of polymer by a pair of rollers (see MELT STRENGTH).

NORMAL STRESSES (not Viscosity) : Polymer melts when sheared (i.e. when subjected to tangential forces) give rise to perpendicular (NORMAL) STRESSES. This means that when a fluid is flowing in a tube it is less compressed in the axial direction than in the radial direction. These NORMAL STRESSES are responsible for the phenomenon of EXTRUDATE SWELL at the exit of the die. Polymers containing a high molecular weight tail tend to give larger NORMAL STRESSES (i.e. they are more elastic).

MELT STRENGTH: A measure of the extensional viscosity of polymer melts. It represents the maximum tension that can be applied to the melt without rupture or tearing. Usually a capillary viscometer is used to extrude a polymer strand and the strand is pulled till rupture by a pair of rollers.
--- source : http://www.polydynamics.com/fra_glossary.htm -------

also refer to : Harvard Non-Newtonian laboratory
http://stokes.harvard.edu/nonnewtonian/extension/experiment.html

Good Luck

Rex

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: : 저는 점도의 종류가 절대점도와 동점도로만 구분되는지 알았는데, 얼마전에 normal, extentional, elonggational viscosity라고 분류되기도 한다고들었습니다. 이것들에 대해서는 다른 참고자료에서 찾아보기힘든대요. 혹시 아시는 것이 있으면 설명좀 부탁드립니다. : ================================ : : All you ask is rhological terminologies. : EXTENSIONAL (= ELONGATIONAL) viscosity, : NORMAL Stresses, ELASTICITY etc.. : I suggest you to refer some of Polymeric , Rheology text books as follows, : (1) Polymer Processing and Structure Development : by Arthur N. Wilkinson, Anthony J. Ryan : Paperback - 304 pages (April 1999) : Kluwer Academic Pub; ISBN: 0751403636 : (2) Polymer Processing fundamentals : Tim A Osswald : ISBN US: 1-56990-262-3 : Published: 1998 : Edition: Softbound 192 pages : Hanser Gardner : ------------------------------------ : Source : http://www.polydynamics.com/fra_glossary.htm : ELONGATIONAL VISCOSITY ( = EXTENSIONAL VISCOSITY) : : The resistance to extension (while the (common) viscosity term describes the resistance to shearing). For Newtonian fluids the elongational viscosity is equal to 3x viscosity (3 is known as the Trouton Ratio). : Polymers are non-Newtonian and the elongational viscosity is usually between 3x viscosity and 100x viscosity. Melt strength is just a rough engineering measure of the elongational viscosity, determined from the force required to break an extruded strand of polymer by a pair of rollers (see MELT STRENGTH). : NORMAL STRESSES (not Viscosity) : Polymer melts when sheared (i.e. when subjected to tangential forces) give rise to perpendicular (NORMAL) STRESSES. This means that when a fluid is flowing in a tube it is less compressed in the axial direction than in the radial direction. These NORMAL STRESSES are responsible for the phenomenon of EXTRUDATE SWELL at the exit of the die. Polymers containing a high molecular weight tail tend to give larger NORMAL STRESSES (i.e. they are more elastic). : MELT STRENGTH: A measure of the extensional viscosity of polymer melts. It represents the maximum tension that can be applied to the melt without rupture or tearing. Usually a capillary viscometer is used to extrude a polymer strand and the strand is pulled till rupture by a pair of rollers. : --- source : http://www.polydynamics.com/fra_glossary.htm ------- : also refer to : Harvard Non-Newtonian laboratory : http://stokes.harvard.edu/nonnewtonian/extension/experiment.html : Good Luck : Rex

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