Torsion geometry between parallel plates

FIG. 5-1. Geometries, coordinates, and dimensions for investigations of viscoelastic liquids, (a) parallel plate simple shear (b) annular pumping (c) rotation between coaxial cylinders (d) torsion between cone and plate (e) torsion between parallel plates (/) axial motion between coaxial cylinders. 

Most rheological measurements measure quantities associated with simple shear shear viscosity, primary and secondary normal stress differences. There are several test geometries and deformation modes, e.g. parallel-plate simple shear, torsion between parallel plates, torsion between a cone and a plate, rotation between two coaxial cylinders (Couette flow), and axial flow through a capillary (Poiseuille flow). The viscosity can be obtained by simultaneous measurement of the angular velocity of the plate (cylinder, cone) and the torque. The measurements can be carried out at different shear rates under steady-state conditions. A transient experiment is another option from which both y q and ]° can be obtained from creep data (constant stress) or stress relaxation experiment which is often measured after cessation of the steady-state flow (Fig. 6.10). 

The samples were cured with 0.2, 0.4, 0.8 and 1.6 wt.% dicu-myl peroxide. In this way, we obtained twelve different networks with great variations in relaxation Intensities. Dynamic mechanical measurements were performed In torsion in the linear region (deformations smaller than 5 %) with a mechanical spectrometer, using the parallel-plate geometry. The frequency ranged from 0.01 to 15 Hz and the temperature was usually between 300 and 435 K. 

The viscoelastic parameters are generally measured by dynamic oscillatory measurements. Apparatus of three different configurations can be used cone and plate, parallel plates, or concentric cylinders. In the case of cone and plate geometry, the test material is contained between a cone and a plate with the angle between cone and plate being small (<4°). The bottom member undergoes forced harmonic oscillations about its axis and this motion is transmitted through the test material to the top member, the motion of which is constrained by a torsion bar. The relevant measurements are the amplitude ratio of the motions of the two members and the associated phase lag. From this information it is relatively simple to determine G and G". 

PIG. S-S. Identification of normal stresses in different experimental geometries, (a), rotation between coaxial cylinders (b), torsion between cone and plate or parallel plates (c) annular axial flow between coaxial cylinders. 

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