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New Driving Unit for the Direct Measurement of Yield Stress with a Stress Controlled Rheometer

Authors :
Shahnazian Hamid
Odenbach Stefan
Source :
Applied Rheology, Vol 18, Iss 5, Pp 54974-1-54974-7 (2008)
Publication Year :
2008
Publisher :
De Gruyter, 2008.

Abstract

Investigations of rheological properties of ferrofluids have shown strong changes of the viscosity in magnetic fluids with an applied magnetic field. The change of the viscosity – the magnetoviscous effect – can theoretically be described with chain and structure formation under the influence of a magnetic field. Moreover, the formation of these structures leads to the appearance of viscoelastic effects or other non-Newtonian features like yield stress in ferrofluids with an applied magnetic field. With a shear rate controlled rheometer – as it as been used in former experiments – the yield stress could not be investigated directly. Therefore the results concerning a field dependent yield stress based on an extrapolation of shear controlled measurements. For the direct investigations of the yield stress, a dedicated stress controlled rheometer is required, allowing direct investigations of the magnitude and field dependence of this effect. In this work the design of the stress controlled rheometer with its main parameters has been described in detail. The rheological investigations with differently composed fluids show that the stress controlled rheometer enables direct measurements of even small yield stresses in ferrofluids as well as large effects like they are found in magnetorheological fluids (MRF).

Details

Language :
English
ISSN :
16178106
Volume :
18
Issue :
5
Database :
Directory of Open Access Journals
Journal :
Applied Rheology
Publication Type :
Academic Journal
Accession number :
edsdoj.43b6b7516cb8414f98502c288845a9db
Document Type :
article
Full Text :
https://doi.org/10.1515/arh-2008-0019