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Experimental Measurements and Numerical Simulation of Bridge Construction Welding at Low Temperatures

Author(s): Radoslav Konar,Marek Patek,Milos Mician / Language(s): English Issue: 3A/2014

This article describes experimental measurements and welding simulation by welding of bridge construction with thickness 30mm. The welded bridge plate was made from steel S355. Welding was carried out at low ambient temperature. Welding parameters and temperature cycles were measured during welding. Deformations of welded construction were obtained using optical system TRITOP before and after welding process. Experimental results except for deformations were used as boundary conditions for FEM simulation in SYSWELD. Temperature cycles, angular deformations and residual stresses were computed. The values of computed and measured angular deformations are almost identical. It follows that SYSWELD is able to predict angular and linear deformation with a good accuracy.

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Statistical Analysis of Wind Speed Data Based on Weibull and Rayleigh Distribution

Author(s): Ivana Pobocikova,Zuzana Sedliackova,Jan Simon / Language(s): English Issue: 3A/2014

In this paper the wind speed data from Meteorological observatory Bratislava-Mlynska dolina were statistically analyzed. The data were analyzed based on Weibull and Rayleigh distribution. The distribution parameters were estimated using maximum likelihood method. The both distributions were compared for their performance using the coefficient of determination and the root mean square error. The results indicate that the better performance can be obtained by the Weibull distribution.

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Numerical Finite Element Method Homogenization of Composite Materials Reinforced With Fibers

Author(s): Daniel Riecky,Milan Zmindak,Zoran Pelagic / Language(s): English Issue: 3A/2014

The paper presents the micromechanical modelling of fiber-reinforced composites in order to determine elastic properties of the homogenized material. For this purpose implementation of homogenization theory was required and analyses were performed. The polymer matrix of three-dimensional representative volume element (RVE) of the composites is modelled by the finite element method (FEM). Software for homogenization of material properties uses direct homogenization method which is based on volume average of stresses in the RVE. Homogenization of composite plate is performed by linking MATLAB and ANSYS software. Calculated elastic properties of the homogenized material are given for epoxy matrix reinforced with carbon, fiberglass and kevlar fiber material.

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Observation of Dynamic Processes on Cutting Zone when Machining Nickel Alloys

Author(s): Andrej Czan,Michal Sajgalik,Anton Martikan,Jozef Mrazik / Language(s): English Issue: 3A/2014

Process models of super alloys and included finite element modelling simulations are important for optimizing the metal cutting process, allowing industry to make parts faster, better, and at less cost. Innovative measurement methods of the process can be used to improve and verify the accuracy of these models. With these methods, there are many sources of error when using empirical or exact methods such as infrared radiation thermography to measure the temperature distribution of the tool, workpiece, and chip during metal cutting. Furthermore, metal cutting presents unique measurement challenges due to factors such as the high magnification required, high surface speeds and deformations, micro-blackbody effects, changing emissivity, and primary, secondary and tertiary deformations. As part of an ongoing effort to improve our understanding of the uncertainties associated with these measurement methods, multi-measurement sets of experiments were performed. One set explored how accurately the surface temperature of the cutting tool reflects the internal temperature. This was accomplished by measuring the temperature using a thermal camera in the cutting zone. The second set provided high-speed scanning of dynamic processes such as formation of elastic and plastic deformation. For this measurement, a high-speed scanning system was applied, with a macro conversion lens for monitoring micro-structural changes in deformation areas. The next set applied was necessary for recording dynamic processes by the implementation of a piezoelectric measurement device for monitoring cutting forces. The outputs from this multi-measuring system are the basis for verification of theoretical knowledge from this field and elimination of the uncertainties that arise with computational simulation systems.

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Laser Interferometer Diagnostics of CNC Machine Tools

Author(s): Jerzy Jozwik,Ivan Kuric,Leszek Semotiuk / Language(s): English Issue: 3A/2014

This paper presents diagnostics of selected CNC machine tools performed with XL80 laser interferometer with XC80 environmental compensation unit, temperature sensors and XR20-W rotary axis calibrator, working together with XL80 laser. Furthermore, the paper includes the methodology and results of conducted linear and angular error measurements, which supplied data for further analysis. The conclusion section presents results of conducted experiment. Measurement results were presented in figures, charts and tables

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Determination the Contact Stress Depending on the Load Rate of the NU220 Roller Bearing

Author(s): Milan Vasko,Ardeshir Guran,Lenka Jakubovicova,Peter Kopas / Language(s): English Issue: 2/2013

The purpose of this paper is to present the impact magnitude of the load rate of the roller bearing at mutual slewing of roller bearing rings to the process of contact stresses in rolling element. The roller bearing satisfies prescribed basic static load capacity if it is loaded by the maximum specified load only in the radial direction according to the ISO / TS 16281. The basic static radial load capacity of the cylindrical roller bearing determines the maximum loading for which there is no plastic deformation in the raceways yet. However, the real roller bearings are not loaded only in the radial direction in practice. During operation there exists a mutual slewing of the roller bearing rings. This leads to a change in the conditions of contact and contact stresses. The analysis of the mutual influence of these two parameters was made using finite-element software ADINA.

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Oscillatory Properties of the Solutions of First Order Linear Neutral Differential Equations with "Maxima"

Author(s): Zuzana Malacka / Language(s): English Issue: 2/2013

In this paper we consider a neutral differential equation with "maxima" of the form… We obtained sufficient conditions for oscillation of all the solutions when t → ∞.

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Yeast Growth Influenced by Parallel Combination of Time-Varying and Static LF EMF

Author(s): Roman Radil,Ladislav Janousek / Language(s): English Issue: 2A/2013

Presented article deals with the mechanisms of low frequency electromagnetic field impact on biological structures. Special attention is paid to the theories describing the influence of applied electromagnetic field on microtubule structures and ions bound on the cell membrane surface. These theories are confronted with the experiments presented herein. For better reliability of the experiments, new exposure coil system has been designed and created. Using this exposure system, results are conducted on the eukaryotic cells represented by saccharomyces cerevisiae. Observed effects show a good correlation mainly with ion parametric resonance model predictions proposed by Lednev and are discussed in the scope of further investigation possibilities.

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Analysis of Dielectric Properties of Lithium Phosphate Glasses

Author(s): Peter Hockicko,Peter Bury,Francisco Munoz / Language(s): English Issue: 2A/2013

Dielectric relaxation spectra of lithium phosphate glasses are used to analyze the change of real and imaginary part of complex permittivity including loss tangent of ion conductive glasses. The experimental results getting from a.c. and d.c. electric measurements on Li phosphate glasses are analyzed, discussed and compared. Frequency dependence of the permittivity spectra is found to be consistent with the analysis of d.c. electrical conductivity. The universal a.c. conductivity law (universal dynamic response) for glass ionic conductor was confirmed. Arrhenius graphs constructed from a.c. and d.c. electrical measurements including loss tangent are used to characterize the relaxation processes and transport mechanisms connected with the mobility of conductive ions.

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Separation of Plastic Particles in Electrostatic Field Produced by Electrodes of Optimized Shape

Author(s): Frantisek Mach,Pavel Kus,Pavel Karban,Ivo Dolezel / Language(s): English Issue: 2A/2013

Shape optimization of electrodes for the device for electrostatic separation of triboelectrically charged plastic particles is carried out. The objective function maximizes the efficiency of separation consisting in the highest possible number of particles falling down to the prescribed bins. Electric field in the system is solved numerically, using the fully adaptive higher-order finite element method. The movement of particles in the device influenced by the Coulomb force is determined by means of an adaptive Runge-Kutta-Fehlberg method with a time varying time step. The shape optimization is carried out using a technique based on genetic algorithms. The methodology is illustrated by an example whose results are discussed.

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Novel Approach to Color Texture Retrieval Based on GLCM

Author(s): Miroslav Benco,Robert Hudec,Martina Zachariasova,Patrik Kamencay,Slavomir Matuska / Language(s): English Issue: 2A/2013

The color and texture are very important features in image analysis. In this paper, the combination of these features is presented. Several approaches for color texture features extraction are researched. The improvement of the one-dimensional version of GLCM (Gray Level Co-occurrence Matrix) for color textures was designed. We named this method as Color Level Co-occurrence Matrix (1D-CLCM). The experiments on database of 2600 color images are provided. Finally, the evaluation and comparison of image retrieval results for separate methods are presented.

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Spectral Transmission Characteristics of Advanced Amplitude Modulation Formats

Author(s): Daniel Benedikovic,Jan Litvik,Michal Kuba,Milan Dado / Language(s): English Issue: 2A/2013

In this paper we focus our attention on numerical investigation of high-order amplitude modulation format in single-channel transmission systems utilizing different kinds of optical fibers. The aim is to show the spectral behavior of advanced amplitude modulated signals in view of fundamental parameters of fiber-optic system. The investigation is realized by solving the nonlinear Schrodinger equation (NLSE) through the pseudospectral split-step Fourier method (SSFM). The obtained results show that the advanced amplitude modulation formats are sensitive to nonlinear phenomenon and they are more desirable for using at short-haul networks.

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Investigation of the Thermal Sensitive Spectral Response of Chalcogenide Fiber Bragg Grating

Author(s): Eliska Jurisova,Libor Ladanyi,Jarmila Mullerova / Language(s): English Issue: 2A/2013

This contribution presents numerical studies of the nonlinear fiber Bragg grating (FBG). The proposed model corresponds well to chalcogenide FBG as a considerable tool for optical switching. The spectral response of this device is discussed theoretically. Simulations based on the nonlinear coupled mode theory are used for investigating the relationships between the spectral transmission of nonlinear chalcogenide FBG and the grating parameters. The influence of the temperature dependence of FBG is numerically investigated. Numerical results show that the ambient temperature has an influence on the spectral response of FBG. The results are indications for applications in optical switches for all-optical communication networks and this can be important for wavelength division multiplexing optical networks.

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$Photonic Crystal Fiber Modal Interferometer for Refractive Index Sensing$

Photonic Crystal Fiber Modal Interferometer for Refractive Index Sensing

Author(s): Daniel Kacik,Peter Tatar / Language(s): English Issue: 2A/2013

We present a modification of core-cladding intermodal interferometer for refractive index sensing. Its structure consists of double cladding photonic crystal fiber (PCF) as a sensing element. First cladding allows fundamental mode propagation only. Second cladding consists of ring of holes with the average refractive index higher than the basic material of the fiber and it is situated close to interface fiber-external environments. So the cladding mode is confined in the ring of holes and its evanescent field extends to external environment. Advantages of this arrangement against core - cladding interferometers are higher sensitivity and, by suitable choice of refractive index of second cladding holes, the possibility to investigate the external refractive index in the region where phase constants of interfering modes shows an extreme (equalization wavelength) in the spectral region.

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Influence of Selected Parameters on Eddy Currents Attenuation in Non-Destructive Inspection

Author(s): Ladislav Janousek / Language(s): English Issue: 2A/2013

Eddy currents attenuation in conductive materials under non-destructive inspection is analyzed in the paper. Influence of selected parameters of the inspection on the attenuation is studied by numerical means. A circular driving coil is employed to induce eddy currents in conductive plates under harmonic excitation. Outer diameter of the coil is varied together with the clearance between the coil and a plate surface for two plates with different thickness. Attenuation of the eddy current density in plates is studied and the results are analyzed in absolute values and the normalized ones as well. It is demonstrated that the investigated parameters of the inspection have significant impact on the attenuation.

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Definition of Boundary Conditions for the Numerical Model of Transient Temperature field of a Concast Steel Slab

Author(s): Frantisek Kavicka,Josef Stetina,Bohumil Sekanina,Milos Masarik / Language(s): English Issue: 4A/2012

The solidification and cooling of a continuously cast billet, slab or cylinder (generally a concasting) is a very complicated problem of 3-D transient heat and mass transfer. This paper is focused on the derivation of boundary conditions, i.e. the values of the heat transfer coefficient (HTC) on all boundaries of the concasting machine (CCM). The definition of boundary conditions is the most difficult part of the investigation of the thermokinetics of this process. The boundary conditions in the numerical model of the temperature field of the concasting are defined as the heat transfer by convection. This HTC includes the so-called reduced convection coefficient corresponding to heat transfer by radiation. This paper therefore continues with a discussion on heat transfer coefficients under air-water cooling jets, which spray the concasting in the so-called secondary-cooling zone.

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Electrochemical Characteristics of Mg-3al-1Zn Magnesium Alloy Surface with Hydroxyapatite Coating

Author(s): Filip Pastorek,Branislav Hadzima,Pavel Dolezal / Language(s): English Issue: 4/2012

Electrochemical characteristics of Mg-3Al-1Zn alloy surfaces after grinding and/or coating by hydroxyapatite were investigated by voltamperometric tests in 0.9 % NaCl solution. The hydroxyapatite treatments were realised by electrochemical method in water solution of Ca(NO3)2 . 4H2O, (NH4)2HPO4 and H2O2 . The influences of various types of hydroxyapatite treatment processes on corrosion potentials, corrosion current densities and characteristics of passive state were evaluated. Basic potentiodynamic curves obtained from the electrochemical tests were analysed by Tafel analyses. The improvement of short-time electrochemical behaviour after hydroxyapatite treatment of tested alloy surface was reported.

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Short Fatigue Crack Growth in a Residual Stress Field in a 7075 Al-Alloy after Shot Peening

Author(s): Ivo Cerny,Dagmar Mikulova,Jiri Sis / Language(s): English Issue: 4/2012

The paper contains results of an investigation of effects of shot peening on growth of physically short fatigue cracks in a 2.4 mm thick sheet of an aircraft V-95 Al-alloy (a type of a 7075 alloy), clad with a 7072 Al-alloy (Al-Zn1). Using an improved and verified experimental methodology, particularly direct current potential drop (DCPD) method, short fatigue cracks of the length from 0.2 mm to more than 3 mm, most of them between 0.8 - 1.5 mm, were prepared under high cycle fatigue repeated tensile loading of the constant nominal stress range 160 MPa, load asymmetry R 0. Edges of the specimens with already existing short fatigue cracks were then shot peened using two different groups of parameters. Some reference specimens without cracks were shot peened with the same parameters. Microhardness measurement and informative measurement of residual stresses near the peened edges were carried out. Significant retardation of crack growth was observed particularly in case of cracks shorter than 2 mm. The work was completed by a unique measurement of actual crack growth rate throughout the peened area with residual stresses starting with crack length less than 0.2 mm. Different stages of the growth are discussed.

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Surface Remelting of Multi-Phase Sintered Steel

Author(s): Agata Wronska,Agata Dudek,Jacek Selejdak / Language(s): English Issue: 4/2012

This study presents the results of the investigations of the effect of surface remelting using arc welding (GTAW) on the microstructure and selected properties of surface layer of sintered steels 304L and 434L. It was found that in order to improve surface quality in these sinters, remelting should be carried out at lower current intensities, i.e. 30A and 40A. The surface treatment carried out in the study allowed for obtaining an uniform cellular-dendritic microstructure in surface layer. X-ray examinations demonstrated the effect of compressive stress in surface layer, which reduces the risk of cracking on the surface.

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Metamaterial Structures and Possibility of their Application in Microwave Applicator Optimization

Author(s): Katarina Istenikova,Dagmar Faktorova,Adriana Savin,Branislav Hadzima / Language(s): English Issue: 4/2012

Metamaterials are special one-, two- or three-dimensional artificial structures with electromagnetic properties generally not found in nature. Due to the simultaneous negative values of permittivity (ε) and permeability (μ), the wave vector and the vectors of electric- and magnetic-field intensity form a left-handed triplet with the result of antiparallel phase and group velocity and backwave propagation. These unique properties of the left-handed materials have allowed novel applications and devices to be developed. In this paper the metamaterial structures based on the split ring resonator approach for optimization of microwave applicator characteristic are used. The main field of the study is absorption of microwave-frequency field in human arm model and improvement of microwave applicator properties such a directivity and gain by means of simulations performed in CST Microwave Studio environment.

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