Wojciech Horak

INVESTIGATION OF MR FLUIDS IN THE OSCILLATORY SQUEEZE MODE

Abstract The paper summarises the results of laboratory testing of three commercially available magnetorheological (MR) fluids operated in the oscillatory squeeze mode. Tested fluids include the Basonetic 204 and Basonetic 4035 (BASF) and MRF-122EG (Lord Corporation). The oscillatory squeeze mode produces large forces at small displacements. This feature may be well utilised in fabrication of new MR devices. The purpose of the experiments was to evaluate the suitability of MR fluids for applications in MR vibration dampers being developed under the current research project. The results enable a comparative analysis of investigated fluids and verification of phenomena encountered in the oscillatory squeeze mode and reported in the literature.

Numerical Simulation and Experimental Validation of the Critical Pressure Value in Ferromagnetic Fluid Seals

Ferrofluids have various engineering applications, and one of them is magnetic fluid seals. Development for this design is a complex process, which requires knowledge about ferrofluid physical properties and magnetic field distribution inside the sealing gap. One of the most important parameters of ferromagnetic fluid seals is a critical pressure value. It is a pressure at which rapid leakage will occur. This publication presents the results of critical pressure value obtained from experimental studies and calculations based on numerical simulations. Shape of sealing stage, volume of ferrofluid, and volume of permanent magnet used in seal construction were taken into account. Experiments and calculations were performed for four ferrofluids differ in saturation magnetization, density, and zero magnetic field viscosity.

Tightness testing of rotary ferromagnetic fluid seal working in water environment

Purpose – The purpose of this publication is to determine the influence of selected factors on the durability and the tightness of ferrofluid seals working in water environments. Ferromagnetic fluid (FF) seals are one of the most common applications of magnetic fluid. New applications can be developed by extending the capabilities of these seals in fluid environments, especially in water. Design/methodology/approach – Tests were performed using ferrofluids with differing physical properties like density, dynamic viscosity and saturation magnetization. Working conditions, such as water pressure and peripheral speed, were taken into account. Findings – A mathematical description which allows the selection of an appropriate ferrofluid and the determination of the operating parameters of an FF seal was developed. Originality/value – This study concerns the influence of peripheral speed, water pressure and magnetic fluid properties on seal tightness.

Measurement of Normal Force in Magnetorheological and Ferrofluid Lubricated Bearings

Preliminary analysis of magnetorheological fluid usability in fluid lubricated bearings has been described in the present study. Results of the study aimed at rheological properties of chosen fluids, which possess magnetic properties (both ferrofluids and magnetorheological fluids) with respect to their application in slide bearings have been presented Preliminary analysis of potential advantages related with the magnetic fluid bearing construction was carried out. Results of measurements of normal force developed within magnetorheological fluid and ferrofluid in result of magnetic field action at various shear rate values have been presented.

RHEOLOGICAL PROPERTIES OF MR FLUIDS RECOMMENDED FOR USE IN SHOCK ABSORBERS

Abstract The paper summarises the results of laboratory testing of rheological behaviour of (magnetorheological) MR fluids designed for use in shock absorber and vibration dampers. The experiments used a rotational rheometer with an extra chamber inside which a uniform magnetic field can be generated. Underlying the description of rheological properties of fluids is the Herschel-Bulkley’s model of viscous- plastic substances. The aim of the experiment was to determine the shear stress, yield stress, the yield factor and the power-law exponent depending on the magnetic flux density, followed by the comparative study of rheological parameters of investigated fluids.

Tuning of elasticity and surface properties of hydrogel cell culture substrates by simple chemical approach

When designing materials for tissue engineering applications various parameters characterizing both materials and tissue have to be taken into account. The characteristics such as chemistry, elasticity, wettability, roughness and morphology of the substrates surface have significant impact on cell behavior. The paper presents biopolymer (collagen/chitosan) based hydrogel materials with tunable elasticity and surface properties useful for fabrication of substrates for cell culture. Using simple chemical approach involving the change in concentration of crosslinking agent (genipin) and composition of the reaction mixture the hydrogels characterized with various features were obtained. Detailed analysis of morphology, topography, roughness and elasticity of surface performed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and rheological measurements has shown that the topographical aspects and roughness parameter can be modulated in nanoscale regime (13-47 nm). Substrates elasticity could be modified in a wide range (0.2-270 kPa). Biological in vitro studies on fibroblasts behavior revealed that the materials prepared provide satisfactory conditions for cell culture, ensuring their high viability, good adhesion and normal morphology. The genipin crosslinked collagen-chitosan hydrogels characterized by denser fiber structure, higher elasticity and lower surface roughness are the most attractive supports for fibroblasts cultivation. The results obtained indicate that the properties of the materials developed can be easily tailored to the needs of the given type of cells.

Collagen/chitosan/hyaluronic acid – based injectable hydrogels for tissue engineering applications – design, physicochemical and biological characterization

Studies on synthesis, physico-chemical and biological properties of novel biomimetic materials, potentially useful as injectable hydrogels are presented. These materials are in situ prepared chemically crosslinked collagen/chitosan/hyaluronic acid-based hydrogels exhibiting potential for tissue regeneration. Optimization of hydrogels involved testing the effect of various concentration of crosslinking agent (genipin) as well as different ratios of biopolymers used on their properties. The changes in the content of hyaluronic acid and in the genipin concentration used have been shown to be crucial. Employing the highest concentration of crosslinking agent studied (20 mM) the hydrogels of compact structure, characterized by good mechanical properties and prolonged degradation profile can be obtained. Changing the HA content in sol mixture the hydrogel of various wettability; more or less hydrophilic when compared to pure collagen/chitosan hydrogels can be fabricated. The in vitro cell culture study has shown that the surface of the prepared materials ensures suitable biocompatibility. These hydrogels can support the proliferation and adhesion of MG-63 cell line as it was demonstrated using Alamar Blue assay and SEM observations. It is believed that the collagen/chitosan/hyaluronic acid hydrogels crosslinked with genipin are particularly promising materials for bone regeneration procedures, especially attractive for regeneration of small bone losses. This is the first paper in the litearature presenting results of studies on that type of biopolymeric injectable hydrogels chemically crosslinked with genipin.

Analysis of Force in MR Fluids during Oscillatory Compression Squeeze

Abstract This study investigates the behaviour of MR fluids in the oscillatory compression squeeze mode. Experiments were performed on commercially available MR fluids in the purpose-built experimental set-up. The influence of MR fluid’s properties and magnetic flux density on the force generated during the squeeze mode was investigated.

THE INFLUENCE OF SELECTED FACTORS ON AXIAL FORCE AND FRICTION TORQUE IN A THRUST BEARING LUBRICATED WITH MAGNETORHEOLOGICAL FLUID

Magnetic fluids belong to the class of materials in which rheological properties can be controlled by magnetic fields. Magnetic fluids are suspensions of ferromagnetic particles in a carrier fluid, and the magnetic field can change their internal structure. This phenomenon is fully reversible, almost instantaneously. * AGH University of Science and Technology, Faculty of Mechanical Engineering and Robotics, al. Mickiewicza 30, 30-059 Krakow, Poland, e-mails: horak@agh.edu.pl, jsalwin@agh.edu.pl,

ANALYSIS OF THE POTENTIAL USAGE OF SELECTED MAGNETIC FLUIDS IN THRUST SLIDE BEARINGS

Magnetic fluids are substances whose rheological properties can be actively influenced by treatment with a magnetic field. Two main types of magnetic fluids can be distinguished: ferromagnetic fluids, and magnetorheological fluids. Ferrofluids are mostly used in sealing engineering, whereas magnetorheological fluids are usually applied in controlled systems for the dissipation of mechanical energy, like brakes and dampers. The ability to control the rheological properties * AGH University of Science and Technology, Faculty of Mechanical Engineering and Robotics, al. Mickiewicza 30, 30-059 Krakow, Poland, e-mails: horak@agh.edu.pl, jsalwin@agh.edu.pl,