Keywords: experimental mechanics, identification, smart materials, magnetorheological fluids, magnetorheological composites.

This paper presents experimental measurements of energy dissipation in originally manufactured MagnetoRheological Composites (MRC) and their modelling. Composites were prepared as elastic porous matrices filled with MagnetoRheological Fluid (MRF). Intensity of magnetic field (H) were changed entailing variety of composite properties and shifts of mechanical fields (amplitude of strain and frequency f). Spectrum of mechanical load had sine form with various frequencies. The dependence of energy dissipation and maximal stress in damper upon mechanical as well as magnetic characteristics was examined. The original experimental stand has been constructed to carry research. A qualitative analysis of experimentally obtained data was done and four-parametric, viscoplastic material model based on this results was proposed.

MagnetoRheological Fluids (MRF) belong to the group called Smart Magnetic Materials. They are dispersions of magnetically soft particles - diameters equal to a few microns in non magnetic carrier fluid. Under an influence of external magnetic field chains form causing an increase of the fluid viscosity (in a few milliseconds).

That is a reversible process. MagnetoRheological Composites (MRC) are materials based on MRF so it is also possible to control their properties by changing an external magnetic field strength. Additionally these materials have matrix properties. On the contrary to MRF it is possible to form their shape. Thanks to the use of low cost materials for matrix (such as natural rubber, silicon etc.) MRC may be less expensive than the same volume of MRF [1,2].

Magnetorheological Fluids and Magnetorheological Composites thanks to their unique properties have many applications. The most popular applications are dampers and clutches [3,4]. However these materials are also in use for example in high precision polishing and in medical therapy.

For this type of material, the most adequate is viscoelastic material model for stress below yield point and viscoplastic for stress above because of sensibility on a velocity of the deformation (with magnetic field and without it). The Bingham material model is most widely applied. This model is very simple and it does not allow describing more difficult magnetorheological phenomenon.

Damping properties of MRC made by ourselves were essential aim of studies [5]. This enabled optimal choice of control method of magnetic and mechanical fields as well as identification of mathematical model. Parameters varied in the range following from anticipated applications in real constructions.

In this paper are presented unique experimental set-up used for testing magnetorheological composites in shearing mode under cyclic loading and basics results obtained from the experiment. The attempt to identify main parameters in four-parameters model (viscoelastic/viscoplastic) have been done. It clearly shows that this model describes well the magnetorheological composite behavior.

1

J.D. Carlson, "Low-cost mr fluid sponge device", Proceedings of the 7th International Conferences on Electro-rheological Fluids and Magnetorheological Suspension, World Scientific, 621-628, 1999. doi:10.1106/CG4J-V704-9LPH-GEC0

2

M.J. Chrzan, J.D. Carlson, "MR fluid sponge device and their use in vibration control of washing maschines", Lord Corporation, 2000.

3

J. Kaleta, D. Lewandowski, "The methodology of testing magnetorheological damper under cyclic loading conditions", XIX Sympozjum Zmeczenie i Mechanika Pekania, Bydgoszcz, Poland, 2002 (in polish).

4

www.rheonetic.com

5

J. Kaleta, D. Lewandowski, P. Zajac, "Experimental Identification of Magnetorheological Composites and Elastomers Properties", Fourth International Conference on Materials Structure & Micromechanics of Fracture, Brno, Czech Republic, 2004.

6

J. Kaleta, D. Lewandowski, "Damping in selected magnetorheological composites under cyclic loading", 3rd International Conference Fracture Mechanics of Materials and Structural Integrity, Lviv, Ukraine, 2004.

7

J. Kaleta, D. Lewandowski, G. Zietek, "Viscoplastic material of magnetorheological composite for cyclic loading", 3rd International Conference Fracture Mechanics of Materials and Structural Integrity, Lviv, Ukraine, 2004.

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