Index of content:
Volume 31, Issue 5, July 1987
31(1987); http://dx.doi.org/10.1122/1.549928View Description Hide Description
The molecular network theory due to Yamamoto has been considered, and the effect of modeling the network segments as non‐Gaussian chains has been investigated. By using a non‐Gaussian free energy expression for the entanglement creation function and a constant breakage function, one finds that the resulting material functions will depend on the number of subunits in the network segments. For short segments, an initial increase with shear rate occurs in the viscosity, which can be attributed to the increased energy of dissipation during their deformation by the applied flow field. Introduction of a slip coefficient to remove the affine deformation assumption results in shear thinning behavior, which becomes more pronounced for long polymer segments. Depending on the network segment length and the slip coefficient, it is shown that our choice of entanglement creation and destruction functions leads to the results of Lodge's theory for affine non‐Gaussian chains on one hand, and to Fuller and Leal's predictions for non‐affine Gaussian chains on the other.
31(1987); http://dx.doi.org/10.1122/1.549926View Description Hide Description
Steady, two‐dimensional flows of Bingham fluids are analyzed by means of a modified constitutive relation that applies everywhere in the flow field, in both yielded and practically unyielded regions. The conservation equations and the constitutive relation are solved simultaneously by Galerkin finite element and Newton iteration. This combination eliminates the necessity for tracking yield surfaces in the flow field. The analysis is applied to a one‐dimensional channel flow, a two‐dimensional boundary layer flow, and a two‐dimensional extrusionflow. The finite element predictions compare well with available analytic solutions for limiting cases.
31(1987); http://dx.doi.org/10.1122/1.549929View Description Hide Description
The stress relaxation of chemically leavened doughs was studied after lubricated uniaxial compression to deformations as high as 70% at compression rates from 0.2 to 5.0 cm/min. A relaxation function was determined for the dough using the BKZ elastic fluid theory and was found to be independent of testing rate.
31(1987); http://dx.doi.org/10.1122/1.549930View Description Hide Description
We propose an approach to use a light‐scattering technique as a probe for measuring the rheological properties of semidilute solutions of polymer molecules. The heterodyne spectrum of scattered light is related to the displacement vector of the excited sample. Taking the cross‐correlation function of the scattering intensity and the exciting electrical signal, it is possible to show that the phase difference between the disturbance and the response of the system can be obtained; furthermore, the ratio between the amplitudes of the disturbance and the response can also be obtained up to a normalization constant. Using this information, it is possible to obtain, with some initial reference, the linear rheological behavior of the polymer sample as a function of the exciting frequencies.
31(1987); http://dx.doi.org/10.1122/1.549948View Description Hide Description