Volume 23, Issue 1, February 1979
Index of content:
23(1979); http://dx.doi.org/10.1122/1.549513View Description Hide Description
Experimental methods of measurement of the flow velocity distribution of a rigid PVC through a slit and a cylindrical die were developed. In particular, the slip of the polymer at the wall of a slit die has been shown by the optical observation of the displacement of tracers mixed with the melt. The effect of lubricants on the flow velocities has been shown and a law of variation of the fluid velocity at the wall has been proposed. These data, brought together with the kinetics of the PVC thermal degradation, can be used to compute the transit time of the polymer in a die and a thermal residual stability after extrusion. On this basis, it is possible to adjust the output rates, the temperatures, or the geometrical parameters to obtain a product of constant quality during a long extrusion time.
23(1979); http://dx.doi.org/10.1122/1.549514View Description Hide Description
The flow field inside and outside a spherical aggregate considered as a porous medium in a linear shear field is determined. Stresses within the porous solid matrix are calculated when the particle deformation is neglected. The critical shear for an aggregate is given. The viscosity of a dilute suspension of porous spheres is then appreciated and shown to be a decreasing function of the shear strength.
23(1979); http://dx.doi.org/10.1122/1.549533View Description Hide Description
In Part I the entrance flow of a Newtonian liquid into a slit was analyzed, starting from the Jeffery‐Hamel Theory. This resulted in some as yet unproven predictions concerning the velocity and stress distribution. A suitable cell was designed and used to test these predictions. The velocity distribution was determined by tracer particles (bubbles) and the stress distribution by flow‐birefringence. By using suitable inserts the entry angle α was changed between a flat entry and The essentially Newtonian liquids used were polybutene H‐1900 of 5000 P viscosity and the epoxy resin Lekutherm X‐30 of about Under isothermal steady‐state conditions, considering the theoretically necessary, but unrealizable “point sink” assumption, the results confirmed the predictions of the theory concerning both the velocity and stress distribution. The results are very similar to the published ones on molten polymers, showing that the main influence in the entrance‐flow is geometrical, covered by the proposed theory.
23(1979); http://dx.doi.org/10.1122/1.549534View Description Hide Description
In the present research circular sheets of rubber or soft fetal membrane tissue are inflated within the confines of a cylindrical tube under hydrostatic pressure. The resulting deformations, which are surfaces of revolution, are described and analyzed. The experimental method of deforming the membranes was chosen so that the deformation profiles would have physiological similarity to the expansions of the chorioamniotic sac during the period of labor in the final stage of pregnancy. The kinematical response of the fetal membranes is shown to be the same as the kinematical response of rubber. The principal extension ratios are calculated for a rubber membrane for several deformation profiles. From data obtained in deflection experiments with rubber an approximate deflection profile is established. Assuming rubber to be a Mooney material, and using the theory of elastic membranes described by Green and Adkins, displacements, slopes, and second derivatives of a refined deformation profile for rubber are derived as a function of the maximum displacement at the pole. Using these results it is shown that one can evaluate the elastic parameters of human fetal membranes. In this manner one can make a meaningful comparison of the elastic nature of fetal membranes from term pregnancies to the elastic nature of membranes which rupture at various gestational stages.
23(1979); http://dx.doi.org/10.1122/1.549535View Description Hide Description
23(1979); http://dx.doi.org/10.1122/1.549548View Description Hide Description