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70th Annual Meeting (Oct 1998)Paper EE3 |
NECKING AND BREAKUP OF VISCOELASTIC FLUID FILAMENTS IN FILAMENT STRETCHING DEVICES DURING STRETCHING AND SUBSEQUENT STRESS RELAXATION |
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Abstract |
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| We investigate the transient uniaxial stress growth of polymer melts and concentrated solutions in a filament stretching device. Such fluids exhibit much less significant strain-hardening than is typically observed in dilute and semi-dilute solutions such as Boger fluids, and the need for comparison between experimental observation and numerical calculation of the resulting fluid dynamics is correspondingly greater. There are three distinct dynamical regions that can be distinguished during a prototypical stretching and relaxation experiment: (i) during the stretching phase, the filament undergoes a spatially nonhomogeneous extensional deformation, the tensile stress difference increases and the sample develops a ‘necked configuration’ with a profile that depends on the degree of strain-hardening in the fluid; (ii) following the cessation of stretching, there is a short period during which there is little fluid motion and the tensile stresses in the column rapidly relax as predicted following cessation of homogenous uniaxial elongation; (iii) finally, at longer times, fluid motion in the filament leads to further necking and the column can undergo rupture into two distinct domains attached to either endplate. The onset of pronounced filament necking during the imposed elongation and the time to breakup following cessation of stretching are both found to be sensitive functions of the transient extensional viscosity and the magnitude of strain-hardening in the test fluid. Finite element calculations provide good agreement with the experiments and also with a one-dimensional slender filament theory for break-up of a viscoelastic fluid column. Finally, we show how this one-dimensional theory can also be used to derive an experimental motion control algorithm for systematically achieving a homogeneous uniaxial deformation in any viscoelastic fluid undergoing stretching in a filament stretching device. |
Developed by Albert Co, The Society of Rheology Please e-mail suggestions and comments to albertco@umecheme.maine.edu. Application Version: August 1998 |