摘要:

Some new (boundary‐element) computations of the flow over a slot are reported. By studying the Maxwell model, we find the hole pressure effect is−0.24N1for this case, which is close to the−0.25N1result for a second‐order fluid. We believe this accurate result at low Weissenberg numbers is due to the use of tractions as primitive variables in the calculations; this avoids the need to add separately the pressure and extra stress tensors as is usually the case in other numerical methods. Using a modified Phan‐Thien‐Tanner model we were able to perform computations which are a very good fit to the experimental data of Pike and Baird for polystyrene. Various parameters were changed in the MPTT model, and we confirm the approximate validity of the Higashitani‐Pritchard analysis.

ISSN:0148-6055    

DOI:10.1122/1.549970

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549971

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Bourdon tube effects can be a serious problem during fiber‐spinning experiments. Tubing distortions resulting from pressurization of fiber‐spinning devices can cause offset of the zero force readings. Consequently, the measured extensional forces are erroneous, and the effect on the computed axial stresses can be disastrous. The importance of Bourdon effects has been given very little attention, and in several fiber‐spinning studies the problem has not even been acknowledged. The present work reviews steps that were taken to construct a fiber‐spinning apparatus for use with concentrated suspensions of rod‐like particles. With an existing apparatus, offset of the zero force reading was quite large at relatively low pressures (<50 psig). Sources of the offset are examined in detail, and results are presented to illustrate the improvements made with modifications of the apparatus. Although not entirely devoid of offset at high pressures, the final modified apparatus represents a substantial improvement over the earlier versions, especially when high viscosity fluids are used. Of great significance is the fact that the measured offset is very consistent and reproducible, even after completely dismantling, cleaning, and reassembling the apparatus. These improvements have been made while retaining a sensitivity to forces as low as10−4 N,with a linear torsion constant capable of handling forces of order10−2 N.

ISSN:0148-6055    

DOI:10.1122/1.549997

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Using the simulation program of Kermode and Weaire, we have calculated stress‐strain curves for a number of samples of two‐dimensional foam, under extensional shear (planar extension). The elastic constant takes a value close to that of the ideal hexagonal foam (with the same mean cell area) for all the samples studied. Similarly the plastic behavior shows only slight variation among reasonable disordered structures. Stress increases monotonically with strain, with an asymptotic yield stress of the same order as the values calculated by Kermode and Weaire for the hexagonal structure. The stress‐strain relationship is therefore roughly represented by a hyperbolic tangent function.

ISSN:0148-6055    

DOI:10.1122/1.549972

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Exit pressure experiments are performed for three low‐density polyethylene melts. Viscosity and exit pressure data are obtained for a shear rate range of 1–350 reciprocal seconds. The measured pressure profiles are fit by both linear and quadratic functions. Extrapolation of the linear pressure profiles yields negative exit pressures which increase in magnitude with shear rate or shear stress. Extrapolation of the quadratic pressure profiles yields small, positive values for the exit pressures. The curvature in the pressure profiles is attributed to the pressure dependence of viscosity. If the data from quadratic pressure profiles is analyzed using the exit pressure theory the estimation of first normal stress difference agrees with independent measurements for shear rates as high as100 s−1.

ISSN:0148-6055    

DOI:10.1122/1.549973

出版商:The Society of Rheology    

年代:1988

数据来源: AIP