摘要:

A technique for examining frictional effects at a sample/platen interface during uniaxial compression, developed for metals, has been applied to viscoelastic gels and doughs. Flat, ring‐shaped samples of gelatin and wheat starch gels and of a hard wheat flour dough are prepared with an internal ring diameter ofDi.These viscoelastic materials show, in uniaxial compression, the same qualitative behavior as that reported by Male and Cockcroft for metals (J. Institute of Metals,93, 38–46, 1964). When the sample/platen interface is lubricated, that is, when the interfacial friction is low,Diincreases as the deformation increases; when the friction at the interface is high,Didecreases with increasing deformation. With the viscoelastic fluid (dough) the central hole of the ring always closes up at high enough deformations even when the platen/sample interface is initially lubricated except when lubricated Teflon platen surfaces are employed. To a greater extent than observed for metals, the effective frictional coefficient at the gel or dough interface seems sensitive to extent of deformation.

ISSN:0148-6055    

DOI:10.1122/1.549981

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549982

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550001

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

The anomalous behavior associated with polymer adsorption‐gel formation on a surface was investigated for the flow at low shear of aqueous Polyox coagulant and WSR‐301 solutions, containing 0–100 ppm of the polymer, in beds of monosized spheres. The flow measurements were conducted using stainless steel and Jaytron spheres and three sizes in the radius range 0.0796–0.2000 and 0.1187–0.1988 cm, respectively. The effective hydrodynamic thickness of the surface layer was evaluated from the negative effective velocity at the packing surface as an effective increase in the radius of the spheres. For the two Polyox homologs, the surface layer thickness increased with an increase in sphere radius and macromolecular size and exhibited a pseudo‐Langmuir‐type polymer concentration dependence, with a peak at the 30 ppm polymer concentration level. The present evaluations are in qualitative agreement with predictions based on the equation Δ=4AR2nfound for low shear tubular flow of the same solutions. The deviations from the equation are consistent with the expectation of physical entrapment in packed beds. The implications of the results in terms of resistance factors, residual resistance factors, and residual permeability reduction are presented.

ISSN:0148-6055    

DOI:10.1122/1.549992

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

The penalty‐Galerkin finite‐element method is used to simulate the flow of a polystyrene melt over a rectangular slot placed perpendicular to the flow direction. The White‐Metzner constitutive equation is used with a Carreau model viscosity function and a shear rate‐dependent relaxation time defined so that the primary normal stress difference is exactly reproduced by the model in simple shear flow. Values of the stress field predicted by the simulation are compared with those obtained experimentally by means of flow birefringence. As observed by others, the limiting elasticity value as determined by the Weissenberg number (We) for convergence of the algorithm decreased with increased refinement of the mesh. However, good agreement is still found between predicted values of stress using the coarse mesh and those measured by means of flow birefringence. This work suggests that there may be an optimum mesh for a given flow and constitutive equation which will still give physically realistic results. The Weissenberg number for the melt used in the experimental study asymptotically approached a value of about 1.5 with increasing shear stress, suggesting that it may not be necessary to reach excessively high values of We for simulations involving some polymer melts.

ISSN:0148-6055    

DOI:10.1122/1.549983

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

A complex molecular orientation distribution is observed in the injection molding of amorphous polymers. A major contribution is due to the flow‐induced deformation of the polymer molecules during mold filling and incomplete relaxation during cooling, after cessation of flow. In this work a numerical study is undertaken in an effort to resolve the impact of the fluid mechanics of mold filling on the molecular orientation of the final part, as reflected in available birefringence measurements. Viscoelasticity of the polymer melt is accounted for with the multimode Leonov model. A finite‐element solution of the fountain flow problem is obtained and the effect of the flow field on the deformation experienced by the fluid is elucidated. Frozen‐in stresses are calculated based only on material parameters and processing conditions. Predicted birefringence distributions agree well with published experimental results.

ISSN:0148-6055    

DOI:10.1122/1.549984

出版商:The Society of Rheology    

年代:1988

数据来源: AIP