Communications - Scientific Letters of the University of Zilina, 2012 (vol. 14), issue 4
Articles
Changes of Material Properties of Silumin During Age-Hardening
Jan Kohout
Communications - Scientific Letters of the University of Zilina 2012, 14(4):6-10 | DOI: 10.26552/com.C.2012.4.6-10 
Simple phenomenological description of age-hardening kinetics of supersaturated solid solution is presented using the sum of exponential functions with negative arguments containing rate constants whose temperature dependence is described by the Arrhenius equation. To determine the number of exponentials in the sum is very important: it should be sufficiently high to obtain accurate description of kinetics and sufficiently low to keep the simplicity and practical applicability of this description. The HB hardness and growth changes (i.e. relative length increase) of silumin during age-hardening are studied separately and then commonly as various manifestations...
Mechanical Properties of Heat Treated Secondary AlSi12Cu1Fe Cast Alloy at Room Temperature
Lenka Hurtalova, Eva Tillova, Maria Chalupova
Communications - Scientific Letters of the University of Zilina 2012, 14(4):11-18 | DOI: 10.26552/com.C.2012.4.11-18
The contribution describes changes of mechanical properties (strength tensile, absorbed energy and Brinell hardness) in secondary (recycled) eutectic aluminium-silicon cast alloy - AlSi12Cu1Fe during solution treatment. This work presents the influences of the solution treatment by 525 °C, 545 °C and 565 °C with the holding time 2, 4, 8, 16 and 32 hours, water quenching at 40 °C and natural aging with holding time 24 hours. Mechanical properties were measured in line with STN EN ISO at room temperature. Solution treatment has led to changes in mechanical properties, caused by the changes in microstructure including the spheroidization and coarsening...
Structural (Super)Plasticity of Magnesium Materials
Zuzanka Trojanova, Zoltan Szaraz, Oksana Padalka, Talant Ryspaev, Pavel Lukac
Communications - Scientific Letters of the University of Zilina 2012, 14(4):19-25 | DOI: 10.26552/com.C.2012.4.19-25
Superplastic behaviour of two magnesium alloys QE22 and EZ33 having a grain size of 1μm was studied at a temperature of 420 °C and in the strain rate interval from 1 104 to 1 103 s1. The substructure of samples was analysed by the transmission electron microscope before and after deformation. The substructure of samples exhibits an existence of particles in the grain boundaries. These precipitates are very stable even at high deformation temperature and they are reason for the relatively high ductility of alloys. Observed ductility of the WE54/SiCp composite is much lower due to the existence of ceramic particles in the grain boundaries. They inhibit...
Electrochemical Characteristics of Mg-3al-1Zn Magnesium Alloy Surface with Hydroxyapatite Coating
Filip Pastorek, Branislav Hadzima, Pavel Dolezal
Communications - Scientific Letters of the University of Zilina 2012, 14(4):26-30 | DOI: 10.26552/com.C.2012.4.26-30
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...
Short Fatigue Crack Growth in a Residual Stress Field in a 7075 Al-Alloy after Shot Peening
Ivo Cerny, Dagmar Mikulova, Jiri Sis
Communications - Scientific Letters of the University of Zilina 2012, 14(4):31-36 | DOI: 10.26552/com.C.2012.4.31-36
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...
Corrosion-Erosion Waste of Metals in the Duct System of the Recycling Aluminium Furnace
Tatiana Liptakova, Jozef Jandacka, Milan Malcho, Michaela Vojsovicova
Communications - Scientific Letters of the University of Zilina 2012, 14(4):37-42 | DOI: 10.26552/com.C.2012.4.37-42
The corrosion aggressiveness of the environment in the recycling aluminium furnace duct system is very high. Temperature is in the range from 300 to 900 °C and chemical composition of combustion varies according to treated aluminium waste and flue gas flow is turbulent. These conditions are very complicated for construction metal selection. The aim of the work is to investigate corrosion-erosion behaviour of various construction metals in the operating conditions of the duct system. The metals with different chemical composition (unalloyed construction steel, stainless steel and nickel based alloy) were tested by long time experiment in the real work...
Microstructural Analysis of Nickel Superalloy MAR-M247
Petr Jonsta, Zdenek Jonsta, Katerina Konecna, Miriam Gabcova, Karel Hrbacek
Communications - Scientific Letters of the University of Zilina 2012, 14(4):43-47 | DOI: 10.26552/com.C.2012.4.43-47
This paper presents the results of a microstructural phase analysis of the nickel superalloy MAR M247 after casting and different modes of dissolving annealing in the range of 900°C - 1240°C with cooling in water. The alloy in question presents a polycrystalline nickel creepresistant alloy usable especially for highly stressed components in the aerospace and rocket industries. The analysis was performed using a JEOL JSM 6490LV scanning electron microscope with an Oxford Inca x-act x-ray microanalyzer. The presence of minority phases was identified. The study is focused on their possible changes after the application of different modes of thermal treatment.
Surface Remelting of Multi-Phase Sintered Steel
Agata Wronska, Agata Dudek, Jacek Selejdak
Communications - Scientific Letters of the University of Zilina 2012, 14(4):48-53 | DOI: 10.26552/com.C.2012.4.48-53
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.
Fatigue Strength of Nodular Cast Iron with Different Surface Conditions under Bending Loading
Marian Kokavec, Radomila Konecna, Gianni Nicoletto
Communications - Scientific Letters of the University of Zilina 2012, 14(4):54-59 | DOI: 10.26552/com.C.2012.4.54-59
The aim of this study is to evaluate the effects of surface conditions on the fatigue life of nodular cast iron under cyclic plane bending where the maximum stress is reached at the surface of interest. In order to evaluate the effect of surface conditions, fatigue tests were carried out on five sets of specimens with different surfaces. The surface conditions were as-cast, sand blasted, fine ground, nitrided and carbonitrided. The results show differences in fatigue strength, which are associated with the surface conditions. The characteristics of the surface layers in the different test specimens were examined by metallography. The fracture surfaces...
Metamaterial Structures and Possibility of their Application in Microwave Applicator Optimization
Katarina Istenikova, Dagmar Faktorova, Adriana Savin, Branislav Hadzima
Communications - Scientific Letters of the University of Zilina 2012, 14(4):60-64 | DOI: 10.26552/com.C.2012.4.60-64
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...
T- Joints - Experimental and Numerical Analysis
Vincent Kvocak, Pavol Beke, Renata Vargova
Communications - Scientific Letters of the University of Zilina 2012, 14(4):65-72 | DOI: 10.26552/com.C.2012.4.65-72
The article presented focuses on the comparison of the measurement results obtained in laboratory experiments on joints of a lattice girder. Because of the geometric variety of joints, the article presented concentrated selectively on hinged T-joints only. The geometry of this type of joint consists of two fundamental members: the chord and the brace member. The T-joints examined were always composed of the rectangular chord member in combination with a variety of types (rectangular, circular and open) and dimensions of brace members. The scientific research results and evaluations presented characterize the correlations regarding the global resistance...
Noise Attenuation from Tramway Traffic
Miloslav Rezac, Iveta Skotnicova
Communications - Scientific Letters of the University of Zilina 2012, 14(4):73-78 | DOI: 10.26552/com.C.2012.4.73-78
The article describes course and results of experiment, which provided influence of change of acoustic absorption properties of concrete tram track surface by using the recycled rubber on traffic noise attenuation. The experiment was carried out in cooperation of the Faculty of Civil Engineering, VSB-TU Ostrava with the companies: the Ostrava Transport Company Plc, ODS - the Transport Constructions Plc, INTERTECH plus, Ltd. and with the Faculty of Mechanical Engineering, VSB-TU Ostrava [2].
Tunnel Boring Machine Design and Reliability Parameters of a Dynamic Rock-Indentor System
Marcela Malindzakova, Jozef Futo
Communications - Scientific Letters of the University of Zilina 2012, 14(4):79-82 | DOI: 10.26552/com.C.2012.4.79-82
The article deals with the calculation of reliability indicators of system dynamics, between the tunnel boring machine and the rock during the tunnel boring of the exploratory tunnel Branisko. The background deals with a design of a tunnel boring machine as a whole where the observed parts are rolling chisels in relation to the length of tunnel boring, as well as physical and technological properties of disintegrated rock.
Analysis of the Initial Imperfections Effect on the Thin-Walled Cold-Formed Compressed Steel Members
Mohamad Al Ali, Michal Tomko, Ivo Demjan, Vincent Kvocak
Communications - Scientific Letters of the University of Zilina 2012, 14(4):83-87 | DOI: 10.26552/com.C.2012.4.83-87
The paper deals with the influence of initial imperfections and presents fundamental information about experimental and theoretical-numerical research to determinate the load-carrying capacity of thin-walled cold-formed compressed steel members. The investigated members had closed cross-sections made of homogeneous material. The theoretical-numerical analysis in this paper is oriented on the investigation and modeling of initial imperfections effects, caused by production process, on the load-carrying capacities of mentioned members, while the experimental investigation is to verify the theoretical results and to investigate the behavior of mentioned...
The Least Square and the Weighted Least Square Methods for Estimating the Weibull Distribution Parameters - A Comparative Study
Ivana Pobocikova, Zuzana Sedliackova
Communications - Scientific Letters of the University of Zilina 2012, 14(4):88-93 | DOI: 10.26552/com.C.2012.4.88-93
In this paper we study the performance of the least square method and the weighted least square method for estimating the Weibull distribution parameters. In engineering practice these methods are commonly used due to their simplicity. The estimates of the parameters can be calculated easily by the closed-form formula. We consider three estimators of the cumulative distribution function and the weight factor proposed by Bergman (1986). The methods are compared in terms of the root mean square error and sample size. The comparison is based on the Monte Carlo simulation. The comparison shows that the weight factor improves the accuracy of the estimation...
The Role of Shot Peening in Increasing X70 Steel Fatigue Properties
Katarina Mikova, Mario Guagliano, Otakar Bokuvka, Libor Trsko, Frantisek Novy
Communications - Scientific Letters of the University of Zilina 2012, 14(4):94-98 | DOI: 10.26552/com.C.2012.4.94-98
The paper presents the authors' results of experimental examination of pipeline steel X70 fatigue properties before and after shot peening application, including relaxation of residual stresses during rotating bendi ng fatigue loading (f 30 Hz, T 20 5 °C, R 1). The obtained results confirmed the positive effect of surface hardening realized by shot peening. The fatigue properties incl. fatigue limit were higher after shot peening and this effect was visibly higher for notched specimens than for smooth specimens. During rotating bending fatigue loading the residual stresses in subsurface layers relaxes which decreases the strengthening effect after...
Fatigue Crack Growth in A 7075 Al-Alloy with Evaluation of Overloading Effects
Ivo Cerny
Communications - Scientific Letters of the University of Zilina 2012, 14(4):99-105 | DOI: 10.26552/com.C.2012.4.99-105
Measurement of fatigue crack growth (FCG) in an Al 7075-T7351 alloy of a particularly high homogeneity was carried out as a part of the Proficiency Test Programme on fatigue crack growth measurement, organised by General Electric Aviation, USA, in collaboration with the company Exova in France. To pass the test programme successfully, a particular attention was paid to improve and verify DCPD (direct current potential drop) method being used for the crack length measurement. Additionally, an investigation of effects of overloads on fatigue crack growth and retardation was carried out. In the CT specimens used, the difference between actual and calculated...
Requirements of a Transport System User
Rudolf Kampf, Jan Lizbetin, Lenka Lizbetinova
Communications - Scientific Letters of the University of Zilina 2012, 14(4):106-108 | DOI: 10.26552/com.C.2012.4.106-108
This article deals with the problem of basic parameters which influence the selection of a mode of transport by a transport user. The article suggests the use of Saaty's method as a method suitable for the determination of weights of importance of basic parameters (user's requirements).