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Modeling micropolar electrorheological fluids

Eckart W., Ruzicka M.

International Journal of Applied Mechanics and Engineering

2006

Vol. 11, no 4

813-844

In general, electrorheological fluids are suspensions consisting of solid particles and a carrier oil. If such a suspension is exposed to an electric field, the particles form structures which have essentially the direction of the electric field, resulting in a higher effective viscosity. Of considerable interest is the dependence of this effect on the direction of the electric field. Towards this end, we propose a micropolar theory including appropriate balance and constitutive equations for these suspensions essentially based on the works of Eringen. An appropriate non-dimensionalization is carried out which combines procedures of Eringen for micropolar fluids, on the one hand, and Eckart and Růžička for electrorheological fluids on the other. We then derive constitutive equations for the Cauchy stress and the couple stress and discuss the restrictions imposed on them by the second law of thermodynamics using scaling arguments. To illustrate the enhanced possibilities of micropolar electrorheology, a simple constitutive model which is linear in the strain rate is discussed in a study of a viscometric flow. We finally show that the velocity profile (hence the flow rate) may strongly depend on the direction of the electric field.

Investigations of shear localization in granular bodies within an anisotropic micro-polar hypoplasticity

Tejchman J.

Archives of Hydro-Engineering and Environmental Mechanics

2005

Vol. 52, nr 4

351-371

The paper focuses on the numerical analysis of the effect of texturial anisotropy on shear localization in cohesionless granular materials. For simulation of the mechanical behaviour of a granular material during a monotonous deformation path, a hypoplastic constitutive model was used. To take into account a characteristic length of micro-structure, the constitutive model was extended by micro-polar terms. To take into account texturial effects, the granular hardness was modified. The calculations were carried out with a sand specimen during plane strain compression under constant lateral pressure. A stochastic and uniform distribution of the initial void ratio in the granular specimen was assumed. In addition, shear localization for two different uniform initial void ratios was investigated.