Pracownicy

Streszczenie:
Magnetorheological (MR) fluids are classified as smart materials whose viscoplastic characteristics change under the magnetic field. They are widely applied for dynamic energy dissipation due to their rapid thickening under the external magnetic field. In this work, the core–shell suspension of superparamagnetic iron oxide-based nanoparticles was synthesized and dispersed in silicone oil. Much effort has been made to prepare suspension meeting requirements of MR fluid. The experimental squeezing flow response was studied using a modified split Hopkinson pressure bar (SHPB) with various shear rates. Tests with modified SHPB show that MR fluid rapidly responds to the compression thickening and forming chain-like structures. MR fluid dissipates the energy generated during compression stress tests. This study presents a simple and cost-effective synthesis way suitable for MR fluid formation for its dynamic energy dissipation application.

Słowa kluczowe:
SPION, magnetorheological fluid, split Hopkinson pressure bar, high strain rate, dynamic behaviour

Streszczenie:
In this paper, we present a device which is very sensitive for small changes in the viscosity of the investigated fluid. The main part of the device is a piezo-electric bimorph which consists of the brass shim with two piezo-ceramic layers on the opposite sides. One of them is responsible for generating vibrations, whereas the second one is meant to measure system response which is produced by the damping properties of the surrounding fluid. During the experiment, the cylindrical bar is forced to move by the series of sinusoidal waves with different frequencies and at constant amplitudes. The probe is immersed in the fluid and then the amplitude vs frequency and phase vs frequency curves are obtained. Next, one can determine the viscosity according to a proper mathematical model. The resonant frequency is related to the damping coefficient which depends on the viscosity of the surrender fluid and immersion depth of the probe. The coefficients necessary for calculating viscosity are obtained by fitting the resonance curve to the amplitude vs frequency data obtained from the experiment. The device has been applied to study the anisotropy of magnetorheological fluids. The weak anisotropy of viscosity has been observed. The highest value of viscosity was observed in the case of viscosity measurement in the direction orthogonal to the magnetic field and the lowest in the direction parallel to the magnetic field.

Streszczenie:
The magnetorheological fluid is a functional material that is changing its rheological properties and finally solidifies in a magnetic field. The dynamic behaviour, tested with the use of the Split Hopkinson Pressure Bar is an important issue for description of this material, which is commonly used in different kinds of shock absorbers. This note presents a new idea how to modify the known SHPB set up in order to investigate dynamic properties of magnetorheological materials.

Słowa kluczowe:
Split Hopkinson Pressure Bar (SHPB), Magnetorheological Fluid (MRF), dynamic behaviour, solidification in magnetic field, ferroelements

Streszczenie:
Monolithic, homogenous ballistic shields consisting of a single thick, high-hardness and high-strength steel plate are rarely applied in modern combat vehicles. Currently, a popular armour concept is a multilayered shield since it is expected that the kinetic energy of a threat may be dissipated by transmission through materials with different properties and also by multiple interface reflections. Searching for a maximum ballistic protection at minimum weight inspires applications of various materials which complementary behaviour provides a high protective efficiency without excessive mass. The preliminary experimental investigation presented in the paper aimed to verify behaviour of two prototyped laminated armours under impacts of small-calibre projectiles (cal. 7.62). The main interest lied in impact properties of materials proposed as the intermediate layer. The first tested concept was a laminated steel armour with the 10 mm thick rubber interlayer. In the second armour, the intermediate layer consisted of a magnetorheological fluid.

Słowa kluczowe:
energy absorption, rubber, magnetorheological fluid, protective properties

Streszczenie:
The extension of viscoplastic model of Perzyna for the field of magnetorheological materials is proposed. Perzyna’s approach is adopted to identify the mechanisms of microscopic rearrangement of ferroelements producing visible increase of material stiffness, in particular increase of shear modulus. The project of laboratory test stand is presented. It is based on Split-Hopkinson pressure bar set-up equipped with container for magnetorheological fluid and coil to control it

Słowa kluczowe:
magnetorheological fluid, magnetorheological gel, Perzyna viscoplastic model, Split-Hopkinson pressure bar

Streszczenie:
The magnethoreological material is based on the ferroparticles immersed in carrying fluid. The acting magnetic field is forcing ferroelements to connect into characteristic structure - braids. Behaviour of the magnethoreological material at the high strain rates will be described by Perzyna model. The created model will be verified with use of dedicated laboratory set up.

Słowa kluczowe:
magnethoreological material, viscoplasticity model, dynamic behaviour, ferroelements.

Streszczenie:
The microsized (~10µm) ferroelements build the structure of magenthoreological (MR) fluid. This two phase material in neutral state behaves as a fluid but in magnetic field becomes a solid and has properties of elasto-viscoplastic material. This is due to the skeleton made by ferrolements connected into braids. The aim of the paper is to identify the physical mechanisms of deformation of such a structure with use of own set up for in situ microscopic observations.

Słowa kluczowe:
magnethoreological solids, viscoplasticity, ferroelements, compression test, shear banding

Streszczenie:
Tungsten boride compounds are very promising new hard and super - hard materials. This kind of materials could be used in production of high-speed tools, durable bearings and nonabrasive surfaces. The hardness of tungsten borides strongly depends on boron content as well as material microstructure. For example hardness of W2B is about 12.4 GPa, WB hardness is 18 – 36 GPa, WB2 hardness is 28.5–39.7 GPa and WB3 hardness is 28.6 – 36.9 GPa. Moreover production of tungsten borides in the form of layers or nano -grained structured increase its hardness even above 40 GPa. Although the properties of tungsten boride structures are known from theoretical calculations, the data concerning structures produced experimentally are scare. Therefore, the properties of tungsten boride layers deposited by pulsed laser deposition (PLD) process are investigated in this paper. Layers were deposited using two types of targets: with boron to tungsten ratio of 2.5:1 and 4.5:1 and with the use of two laser wavelengths: 355 and 1064 nm.

Słowa kluczowe:
pulsed laser deposition, tungsten borides

Streszczenie:
Magnetorheological materials are commonly used in technical devices because of specific behaviour in magnetic field. The magnetoactive particles are immersed in the carried fluid. The material becomes solid under the influence of magnetic field. The structure of solid material consists of the chains of the particles lying along the direction of magnetic field and the material under the stress is deforming as a solid body. The present studies are focused on the microscopic and phenomenological models of non-newtonian fluid. However, the mechanisms of deformation in solidified material under magnetic field require further investigations. The aim of the paper is to present the experimental visualization of the rearrangements of the particles in the activated by magnetic field chains. Basing on microscopic observations, the hypothesis is formulated that the mechanism of micro-shear banding is responsible for inelastic deformation of magnetorheological material. The discussed physical model makes the basis of the material description within the framework of the Perzyna viscoplasticity theory.

Słowa kluczowe:
magnetorheological fluid, magnetorheological gel, Perzyna viscoplastic model

Streszczenie:
Przedmiotem badań niniejszej pracy jest numeryczna rekonstrukcja struktur rzeczywistych pianek otwartokomórkowych w celu wygenerowania reprezentatywnego elementu objetości. Analizowane są dwa rodzaje pianek (ceramiczna i polimerowa), których porowatość wynosi odpowiednio 90% i 94%. Oba rodzaje pianek zostały przebadane z użyciem mikrotomografu komputerowego. Uzyskane dane zostały zaimportowane do programu ScanIP, przy pomocy którego przeprowadzono cyfrową obróbkę uzyskanych obrazów oraz wydzielono fazę reprezentującą szkielet pianki.

Słowa kluczowe:
numeryczna rekonstrukcja, struktury otwartokomórkowe, pianki metaliczne, mikrotomografia komputerowa

Streszczenie:
The subject of te study are metallic open-cell foams. In particular, the foam of Cu skeleton is considered. To simulate the deformation process of such a material the finite element program ABAQUS is used. The tomogram reconstructing the 3D virtual volume of a real foam structure with the use of computed tomography is applied to formulate the finite element model of the convex open-cell foam cube of the edge of 800 voxels created with application of ABAQUS/CAE. The initial cube of convex open-cell skeleton is subjected to three-axial compression applied as uniform displacements normal to the surface of cube faces in order to simulate numerically auxetic foam fabrication process.

Słowa kluczowe:
auxetic foam, micro-tomography, tomograms, negative Poisson's ration, numerical simulation, metallic foam, open-cell foam, foam fabrication

Streszczenie:
The extension of viscoplasticity Perzyna's model for the field of magnetorheological materials is proposed. The model is adopted to identify the mechanisms of microscopic rearrangement of ferroelements producing visible increase of material stiffness, in particular increase of shear modulus. The project of laboratory test stand is presented. It is based on Split Hopkinson Pressure Bar set-up equipped with container for magnetorheological fluid and coil to control it.

Słowa kluczowe:
magnetorheological fluid, magnetorheological gel, Pezryna viscoplasticity model, Split Hopkinson Pressure Bar