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1

Modeling micropolar electrorheological fluids

100%

Eckart W. , Ruzicka M.

International Journal of Applied Mechanics and Engineering

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2006

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tom Vol. 11, no 4

813-844

EN

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.

2

Application of fibre composites in a spindle ram design

80%

Kulisek V. , Janota M. , Ruzicka M. , Vrba P.

Journal of Machine Engineering

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2013

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tom Vol. 13, No. 1

7--23

EN

When compared to steel or cast iron, carbon fibre composites offer excellent tensile and bending stiffness together with significantly smaller density. Research at the Research centre of Manufacturing Technologies in Prague has been aimed at the application of composite materials in structural parts design. Case studies on spindle rams were performed focusing on the design of experimental composite spindle rams and their benchmarking with reference steel components. The cross-section of both parts was 350x350mm and the length was 1200mm. The first design was made as a thick-walled composite body with a minimal amount of steel. The goal was to achieve static stiffness comparable to a reference steel component of the same size. The second design was manufactured as a hybrid structure composed of fibre composites with cork layers and bonded steel reinforcements. The goal was to improve damping of the structural parts in comparison with the steel components. Results of stiffness and modal properties were obtained from experiments and also using FEA. Experimentally obtained damping ratios of composite and reference steel rams were compared with and without the effect of connection interfaces on damping.

3

Influence of bubble approach velocity on coalescence in α-terpineol and n-octanol solutions

61%

Orvalho S. , Stikova L. , Stanovsky P. , Zednikova M. , Vejrazka J. , Ruzicka M.

Physicochemical Problems of Mineral Processing

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2018

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tom Vol. 54, iss. 1

73--80

EN

This work presents results of an experimental study of the influence of the approach velocity on the coalescence of bubbles in aqueous solutions of n-octanol and α-terpineol. Experiments were performed in a coalescence cell allowing synchronized growth of a pair of bubbles in a liquid. High speed camera imaging was used to characterize the growth of bubbles and their interaction in aqueous solution of different concentrations of surfactants. The coalescence efficiency and contact time till coalescence were determined as a function of the approach velocity between bubbles and the concentration of surfactant. It was found that, for both surfactants, when the approach velocity between bubbles was higher than ~1 mm/s, the coalescence efficiency was independent of the approach velocity and that the contact time was independent of the concentration of surfactant. Below ~1 mm/s, both the coalescence efficiency and the contact time were the function of surfactant concentration. For the higher velocities, the suppression of coalescence occurred at concentrations similar to the concentration of immobilization of the surface of free rising bubbles.

4

Effect of cold rolling and annealing on mechanical properties of HSLA steel

51%

Schindler I. , Janosec M. , Mistecky E. , Ruzicka M. , Cizek L. , Dobrzański L. A. , Rusz S. , Suchanek P.

Archives of Materials Science and Engineering

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2009

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tom Vol. 36, nr 1

41-47

EN

Purpose: was to examine effect of the parameters of cold deformation and recrystallization annealing on mechanical properties of a Nb-microalloyed HSLA steel. Design/methodology/approach: Research of strip steel QStE 420 was based on a combination of laboratory cold rolling, recrystallization annealing in vacuum furnace, mechanical (particularly tensile) tests and metallographic analyses. Findings: It was validated that by a sophisticated combination of size of previous cold reduction size and parameters of the following annealing it is possible to impact markedly a set of final properties of particular strips. Formability of the studied HSLA steel rises and vice versa strength properties fall with an increasing temperature of annealing. Research limitations/implications: The experiment should be supplemented by additional TEM analyses explaining the behaviour and role of precipitates. Practical implications: The experimentally obtained particular trends of mechanical properties may be utilized for optimization of conditions of heat treatment of the investigated HLSA steel in a cold strip rolling mill, reflecting the specific requirements for a relation between strength and plastic properties. Originality/value: Experimental potentialities of the Institute of Modelling and Control of Forming Processes in the sphere of cold rolling and heat treatment were introduced in their integrity for the first time.

5

Properties of a Nb-V-Ti microalloyed steel influenced by cold rolling and annealing

51%

Janosec M. , Schindler I. , Palat J. , Cizek L. , Vodarek V. , Mistecky E. , Ruzicka M. , Dobrzański L. A. , Rusz S. , Suchanek P.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 20, nr 1-2

251-254

EN

Purpose: was to investigate impact of cold forming and annealing on microstructural and mechanical properties of HSLA steel. Design/methodology/approach: Testing of Nb-V-Ti microalloyed strip steel was based on a combination of cold rolling, recrystallization annealing, mechanical testing, metallography and TEM. Findings: It was confirmed that by a suitable combination of size of previous cold reduction size and parameters of the following annealing it is possible to influence considerably a complex of mechanical properties of particular strips. Strength as well as plastic properties depended on the course of recrystallization and precipitates' coarsening during annealing. Research limitations/implications: The experiment should be supplemented by the more detailed analyses of microstructure. Practical implications: The results may be utilized for optimization of terms of heat treatment in a cold rolling mill, especially in accordance with specific requirements for a relation between plastic and strength properties of the investigated steel. Originality/value: Research possibilities of VSB-TUO in the sphere of cold rolling of Nb-V-Ti HSLA steel were introduced in combination with the complex approach to processing of the obtained results.