Communications - Scientific Letters of the University of Zilina, 2009 (vol. 11), issue 1
Articles
Deformation Behaviour of Mg-Based Matrix Composites
Pavel Lukac, Zuzanka Trojanova
Communications - Scientific Letters of the University of Zilina 2009, 11(1):5-9 | DOI: 10.26552/com.C.2009.1.5-9 
The influence of various reinforcements on mechanical properties and deformation behaviour of some magnesium alloys was studied. Strength and deformation behaviour were investigated over a wide temperature range. The reinforcement was in the form of short fibres or particles. The volume fraction of the reinforcement significantly influences the properties of a composite. The interface between the matrix and the reinforcement has a great deal of importance in determining the properties of the composite. Thermal stresses generated at the interface play a very important role.
Effect of Short Saffil Fibres and SIC Particles on Mechanical Properties of Magnesium Alloys
Zuzanka Trojanova, Zoltan Szaraz, V. Gartnerova
Communications - Scientific Letters of the University of Zilina 2009, 11(1):10-16 | DOI: 10.26552/com.C.2009.1.10-16
The high temperature mechanical behaviour of composites with the AZ91 and AS21 magnesium alloys matrix, reinforced with short Saffil fibres and SiC particles were investigated. Samples were deformed in compression in the temperature range from room temperature to 300 °C. The yield stress and the maximum stress of true stress-true strain curves decrease with increasing temperature. Light and electron microscopy were used for study of the microstructure of composites. Possible hardening and softening mechanisms are discussed. The increased dislocation density and the shear stress at reinforcing phase/matrix interfaces were found as the most important...
Fatigue Lifetime of 7075 Aluminium Alloy from Ultimate Tensile Strength to Permanent Fatigue Limit
Josef Zapletal, Stanislav Vechet, Jan Kohout, Petr Liskutin
Communications - Scientific Letters of the University of Zilina 2009, 11(1):17-21 | DOI: 10.26552/com.C.2009.1.17-21
The aim of this paper is to study fatigue behaviour of 7075 aluminium alloy at room temperature for both important directions (longitudinal as well as transversal) with respect to the direction of forming. Smooth test bars were subjected to symmetrical push-pull loading at stresses which cover the whole range of lifetime from UTS to permanent fatigue limit. The results are presented above all as S-N curves fitted using suitable regression functions which lead to precise and reliable determination of fatigue limits.
Fatigue Resistance of High-Thickness Al-Alloy Sheets after Water Jet Cutting
Ivo Cerny, Dagmar Mikulova
Communications - Scientific Letters of the University of Zilina 2009, 11(1):22-26 | DOI: 10.26552/com.C.2009.1.22-26
Water jet cutting is a useful advanced technology of separating materials with a great industrial potential due to high cutting speed, precision, shape repeatability and possibilities to be performed automatically with a computer control. It is well known, however, that fatigue properties are particularly strongly affected by surface conditions and quality of surface layer. Water jet cutting was applied to Al-alloy sheets of fairly high thickness, namely 50.8 mm. Fatigue resistance of water cut specimens and failure mechanisms were investigated and compared with those studied using a reference batch of specimens manufactured by fine milling. Character...
Fatigue Properties of Steel with Increased Atmospheric Corrosion Resistance
Marian Bursak, Otakar Bokuvka
Communications - Scientific Letters of the University of Zilina 2009, 11(1):27-30 | DOI: 10.26552/com.C.2009.1.27-30
The paper deals with the influence of cyclic loading (tension-compression, bending and torsion) on the course of the fatigue life and the fatigue limit of advanced low-alloyed strip steel with increased atmospheric corrosion resistance. The tested steel shows, besides very good mechanical properties (Re 380 MPa, A5 30%), also very good fatigue resistance and its fatigue limit/ultimate tensile strength ratio is above 0.5. These properties are provided by a favourable fine-grained structure of the tested steel.
Similarity between Effects of Laves Phase and M6C in Alloy Steels
Jozef Janovec
Communications - Scientific Letters of the University of Zilina 2009, 11(1):31-33 | DOI: 10.26552/com.C.2009.1.31-33
The aim of this work is to summarize the experimental result obtained within the last two decades about the effects of Laves phase and M6C during long-term thermal exposures of alloy steels. The intergranular Laves phase (12CrMoV steel) and/or M6C (3CrMoV steel) particles were found to evoke the anomaly in the kinetic dependence of phosphorus grain boundary concentration. In comparison to other phases usually present in Cr-Mo alloy steels, Laves phase and M6C precipitate after longer periods of annealing and dissolve non-metallic elements such as phosphorus or silicon. A partitioning of originally segregated phosphorus between the matrix and the newly...
Microstructural Material Analysis of Superalloy Inconel 792-5A after High Temperature Exposition
Zdenek Jonsta, Petr Jonsta, Karel Mazanec
Communications - Scientific Letters of the University of Zilina 2009, 11(1):34-38 | DOI: 10.26552/com.C.2009.1.34-38
Aerospace industry often uses nickel superalloys for blades of jet engine turbines. The reason is that this material can satisfy numerous extreme requirements, such e.g. strength even at very high temperatures, resistance to fatigue damage, resistance to fatigue effect of combustion gases, etc. Long-term service life and material reliability is directly linked to its microstructure, or with its stability at long-term exploitation. Presented article deals with analysis microstructural material characteristics of cast variants nickel superalloy of INCONEL 792-5A type. Several strengthening mechanisms are applied in this type of superalloy. Principal...
Basis for Optimal Choice of High Alloyed Structural Materials Used in Chemical and Power Industry
Jiri Kunz, Klara Dalikova, Vladimir Cihal
Communications - Scientific Letters of the University of Zilina 2009, 11(1):39-44 | DOI: 10.26552/com.C.2009.1.39-44
Six types of high alloyed structural materials widely used especially in power and chemical industry were under study. The experimental programme was focused on the research of materials resistivity against high aggressive media and time variable loading. The paper summarizes results of slow-strain rate test, electrochemical measurements (by means of potentiodynamic method, electrochemical noise measurement and electrochemical impedance spectroscopy) and fatigue test. The investigation was completed by fractographic analysis of failed test specimens. Detailed photo-documentation of specimen fractures was obtained by means of scanning electron microscopy.
A Novel Damage State Simulation Method with Shape Memory Polymer
Du Jian-hua, Zhao Yang-dong
Communications - Scientific Letters of the University of Zilina 2009, 11(1):45-49 | DOI: 10.26552/com.C.2009.1.45-49
Shape Memory Polymer (SMP), a kind of smart materials which can memorize its former shape, has the general character of plastics and rubbers. The paper analyzes the present methods of damage simulation in numerical simulation and model test and performs mechanical test to study SMP's shape memory mechanism as LgE-T. A new thinking is put forward to make the stiffness-controlled specimen according to the deficiency of present simulation methods, which could not simulate the damage process. The validating test proves the stiffness-controlled specimen can simulate the damage process of accumulation and has the value of validating the damage identification...
Damage Identification Method with Structural Frequency Data from Modal Test
Du Jian-hua, Ouyang Zhiwei, Zhao Yangdong
Communications - Scientific Letters of the University of Zilina 2009, 11(1):50-54 | DOI: 10.26552/com.C.2009.1.50-54
Testing and analysis technology based on vibration mode is a common method to structural health monitoring and checking. This paper deduces the damage factor used for structural damage evaluation based on test frequency of structure, makes a finite element numerical simulation using ANSYS software and model test to a pressure pipe. Here a stiffness reduction method is utilized to reproduce the damage state of a single-point and multiple-point, damage identification is carried out with a FEM model of redundant pipe. Meanwhile, a model experiment system is designed to validate the efficiency of damage factor with cutting-groove to simulate damage states....
The DFM Control System Based on PLL
Andrzej Popenda
Communications - Scientific Letters of the University of Zilina 2009, 11(1):55-59 | DOI: 10.26552/com.C.2009.1.55-59
A specific structure of control system with double fed machine (DFM) is studied in the paper. The DFM is assumed to be a generator with stator winding connected to the power grid and it produces active and reactive powers. A command vector controlling DFM is transformed to the rotor-oriented coordinate system using angle of transformation. The angle of transformation is estimated in the system by applying a phase locked loop (PLL).Moreover, an example of application of pulse phase locked loop for estimation of voltage vector components is presented in the paper. In conclusion the properties of proposed PLL-based control systems are compared with properties...
The Challenges of Market Research in China
Lena Weick
Communications - Scientific Letters of the University of Zilina 2009, 11(1):60-63 | DOI: 10.26552/com.C.2009.1.60-63
This article analyses the challenges of current market research activities in China. A country that achieved remarkable economic development since the late 1970s and that is still continuing to grow.Firstly a picture of the market research industry in China is provided. Based on the history of market research, the leading companies and the most important types and aims of research are highlighted. The development of the market research industry in the framework of the Chinese market in general leads to challenges in primary and secondary research. Primary research in China is dominated by regional disparities, particularly in terms of language and...
Geothermal Energy and Power Generation in Germany
Gerhard Braunmiller, Peter Horbaj, Natalia Jasminska
Communications - Scientific Letters of the University of Zilina 2009, 11(1):64-66 | DOI: 10.26552/com.C.2009.1.64-66
The EU is the world's largest energy importer, relying on imports for 50 % of its energy needs. With an energy demand forecast likely to grow by 1-2 % a year, that figure will over the coming 20-30 years rise to 70 %.The Geothermie is an inexhaustible energy source. With the supplies, which are stored in our planet, in principle the world-wide power requirement could be covered. The Geothermie, or terrestrial heat, is the warmth stored in the upper (accessible) part of the earth's crust. It covers the energy, as far as it can be extracted and used, stored in the earth, and ranks among the regenerative energies. It can be used both directly, approximately...