|M.Sc Student||Dayan Yosef|
|Subject||Non-Linear Behavior of Magneto-Rhelogical Fluids|
|Department||Department of Mechanical Engineering||Supervisor||Professor Emeritus David Durban|
|Full Thesis text - in Hebrew|
Materials which immediately transform their properties under the effect of a magnetic field are called Magneto-Rheological Fluids (MRF). These fluids are composed of a fluid containing micro metal particles. As long as the magnetic field is active, the material exhibits solid-like properties. When the shear stress reaches a critical threshold, it is "sheared" and reacts like a viscous fluid. The object of the present work is to perform an experimental research on the behavior of magneto-rheologic fluids subjected to the effect of magnetic flux's changing density (B), change of the liquid matrix's viscosity (µ), and change of the metal's particles' concentration (c). After performing a parametric research, the object is to find an appropriate rheological model, which describes the behavior of the magneto-rheological fluids and relates the mechanical and magnetic properties of the material. The most important dependence (regarding the performance of the MR fluid) is the yield stress dependence of the shearing (ty), on (B), for different values of (c). For the purpose of achieving the research work's objectives, rheological measures were made, using a magneto-rheometer, capable of performing rheological measurements, and activation of a magnetic field on the sample of the measured fluid. By using this measuring instrument, we can directly derive the shear stress (τ) as a function of the shear strain rate (γ), for different values of the magnetic flux's density. In addition, after finding the appropriate rheological model for the magneto-rheological fluid, a comparative research was performed, for examining the impact of the changing parameters in the fluid, on the model's parameters. The main findings discovered in this research work are as follows: the constitutive description of the MRF focuses on un-dimensional models. The model chosen, is the Herschel-Bulkley, t=ty+hγn. The purpose is to examine the impact of each parameter in the experiments (µ, c, B) on the variables in the constitutive modal written above. We can see that for the results of the shear stress and the viscosity coefficient, their values rise in an obvious manner as a function of the magnetic flux's density. In addition, we can see, that for high concentrations of metal particles, the values of these variables increase. In a graph of n as a function of the magnetic flux's density, it is clearly seen, that the value of n increases as the magnetic field increases.