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Ilari Jonkkari, Seppo Syrjala
Evaluation of techniques for measuring the yield stress of a magnetorheological fluid

Appl. Rheol. 20:4 (2010) 45875 (7 pages)

The yield stress of a magnetorheological fluid was measured as a function of magnetic flux density using different techniques. The yield stress values were determined by extrapolating the experimental shear stress-shear rate data to zero shear rate with the help of Bingham and Herschel-Bulkley models, and by using stress ramp and dynamic oscillatory tests.To obtain the rheological data, the rotational rheometer equipped with a magnetic field generator and a plate-and-plate measuring geometry was used. The different methods produced yield stress values which were in reasonable agreement with each other.

Cite this publication as follows:
Jonkkari I, Syrjala S: Evaluation of techniques for measuring the yield stress of a magnetorheological fluid, Appl. Rheol. 20 (2010) 45875.

Johanna Aho, Seppo Syrjala
Evaluation of different methods for determining the entrance pressure drop in capillary rheometry

Appl. Rheol. 18:6 (2008) 63258 (5 pages)

Two approaches for determining the entrance pressure drop in capillary rheometry were compared with low-density polyethylene and polystyrene melts as test fluids. Direct measurements with the orifice die were found to yield higher values for the entrance pressure drop, and hence lower values for the wall shear stress, than the Bagley correction method. This was postulated to be caused by the sticking of the melt to the wall of the outlet region of the orifice die. The additional pressure drop created in the outlet region of the orifice die, when the flowing material fills it completely, was also evaluated by means of numerical flow simulation.

Cite this publication as follows:
Aho J, Syrjala S: Evaluation of different methods for determining the entrance pressure drop in capillary rheometry, Appl. Rheol. 18 (2008) 63258.


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