Communications - Scientific Letters of the University of Zilina, 2010 (vol. 12), issue 4
Articles
Deformation Mechanisms Operating during Plastic Flow of An Az63 Magnesium Alloy Studied by the Stress Relaxation Technique
Zuzanka Trojanova, Pavel Lukac
Communications - Scientific Letters of the University of Zilina 2010, 12(4):5-11 | DOI: 10.26552/com.C.2010.4.5-11 
Magnesium alloy AZ63 (Mg-6Al-3Zn) was deformed at temperatures between room temperature and 300 °C. Stress relaxation tests were performed in order to reveal features of the thermally activated dislocation mechanism. Internal and effective components of the applied stress were estimated. Very high values of the internal stress estimated at lower temperatures decrease rapidly with increasing deformation temperature. The apparent activation volume decreases with increasing effective stress. The values of the activation volume as well as the activation enthalpy indicate that the main thermally activated process is most probably the glide of dislocations...
Mechanical Properties and Strain Hardening Behaviour of Magnesium Alloys and Composites
Pavel Lukac, Zuzanka Trojanova
Communications - Scientific Letters of the University of Zilina 2010, 12(4):12-19 | DOI: 10.26552/com.C.2010.4.12-19
Selected magnesium alloys and composites with magnesium alloy matrix were deformed at temperatures between room temperature and 300 °C at constant strain rate. The testing temperature influences significantly the deformation behaviour of the al/loys. The flow stress decreases with increasing temperature. The work hardening rate decreases with stress (strain) and temperature. Above about 200 °C, a dynamic balance between hardening and softening is observed. Stress relaxation tests were performed to identify thermally activated dislocation motion. The main thermally activated process is very probably the glide of dislocation in non-basal planes. The...
Influence of Secondary Phase Precipitation on Resistance to Intergranular Corrosion of AiSi 316l Austenitic Stainless Steel
Katarina Bartova, Maria Domankova, Jozef Janovec
Communications - Scientific Letters of the University of Zilina 2010, 12(4):20-26 | DOI: 10.26552/com.C.2010.4.20-26
The AISI 316L steel after cold working of 40% and subsequent annealing at 750°C for 1, 2, 5, 10, 50, or 100 h was investigated. For the microstructure characterization the light microscopy and the transmission electron microscopy were used. To determine the sensitivity to intergranular corrosion the test was performed according to ASTM A 262, practice A. The transition between non-sensitised and sensitised states was found to be between 1 and 2 h of annealing. Sigma, laves and chi phases were identified in all the analyzed conditions. M23C6 was found to start to precipitate between 5 and 10 h of annealing. Sigma, chi, and M23C6 precipitated mainly...
The Influence of Strain Rate on the Plasticity of Steel Sheets
Jan Michel, Marian Bursak
Communications - Scientific Letters of the University of Zilina 2010, 12(4):27-32 | DOI: 10.26552/com.C.2010.4.27-32
The paper analyses the influence of strain rate on the behaviour of un-alloyed steels with Re 210-550 MPa in the deformation process. It presents and analyses the results of the influence of the strain rates ranging from 103 to 2.5 . 102 s1 on the yield point, tensile strength, elongation and reduction of area. It analyses the non-homogeneity of development of plastic deformation from both, the macroscopic and microscopic points of view, as well as the influence of the strain rate on the development of plastic deformation. Since the intensity of the influence of the strain rate on the properties of materials depends on their internal structure, the...
Failure of Composites with Short Fibers
Milan Zmindak, Daniel Riecky, Josef Soukup
Communications - Scientific Letters of the University of Zilina 2010, 12(4):33-39 | DOI: 10.26552/com.C.2010.4.33-39
Strength-based failure criteria are commonly used with the finite element method (FEM) to predict failure events in composite structures. The laminate analogy is very useful for the calculation of the strength of composite materials with short fibers. The prediction of the laminate strength is carried out by evaluating the stress state within each layer of the laminate based on the classical lamination theory. In this paper FEM is used as a tool to predict the laminate strength. Failure criteria are used to calculate a failure index (FI) from the computed stresses and user-supplied material strengths. The micromechanical analysis has been carried out...
Mutual Reciprocal Interconnection of Relations Describing Creep, Yield Stress and Stress Relaxation
Jan Kohout, Vojtech Hruby
Communications - Scientific Letters of the University of Zilina 2010, 12(4):40-44 | DOI: 10.26552/com.C.2010.4.40-44
The steady-state creep rate increases with testing temperature according to the Arrhenius law and its increase with applied stress is usually described by the power law. Simple multiplication of these two laws leads to the dependence of steady-state creep rate on both the variables. Apparent activation energy and stress sensitivity parameter perform in the combined law as constants but most measurements show their dependence on some of the variables. An equation respecting these experimental facts and simultaneously also based on the Arrhenius equation and the power law is derived and verified using some published results of creep tests. It can be...
Deep-Drawing and Fatigue Properties of Advanced Steel Sheet Stripes
Marian Bursak, Jan Michel
Communications - Scientific Letters of the University of Zilina 2010, 12(4):45-48 | DOI: 10.26552/com.C.2010.4.45-48
Analysis of the deep drawing and fatigue properties is given in this contribution for two advanced micro alloyed sheet steel grades with Yield strength values Re 246 and 382 MPa, respectively. The 2 mm thick steel sheets were hot dip zinc coated. The deep drawing properties were evaluated by tensile testing and by the Erichsen test at different strain rates. For fatigue testing the symmetric bending test was applied. Results showed favorable deep drawing properties of these steel sheets assigned for heavy duty parts in automotive industry. Steel grade with Re 246 MPa had elongation A80 32%, n 0.21, Erichsen number IE 12.5 mm and the steel with...
Effect of Galvanic Metallization, PVD Processes and Thermal Spraying on Fatigue Properties of Plain Structural Steels in the Ultra-High-Cycle Regime
Frantisek Novy, Rastislav Mintach, Otakar Bokuvka
Communications - Scientific Letters of the University of Zilina 2010, 12(4):49-54 | DOI: 10.26552/com.C.2010.4.49-54
This work presents information about the influence of Ni and ZnFe galvanic metallization on the fatigue properties of S235JRG2 steel and about the TiN physical vapour deposition and WC thermal spraying on the fatigue properties of S355J0 steel in the ultra-high-cycle region of loading (N 6106 - 1010 cycles) obtained at high-frequency fatigue testing (f 20 kHz, T 20 3 °C, R 1). Technical coatings are used in order to modify the properties of the surface that is being covered for protection against corrosion but also in order to increase the hardness and resistance to wear. The Ni coating produced by galvanic metallization favourably influences the...
Effect of Inclusions on Fatigue Strength of Heat Treated Components
Vaclav Linhart, Dagmar Mikulova, Ivo Cerny
Communications - Scientific Letters of the University of Zilina 2010, 12(4):55-61 | DOI: 10.26552/com.C.2010.4.55-61
Inclusions significantly affect fatigue properties of quenched and tempered parts. Data about inclusions importance in fatigue crack initiation process were acquired within the framework of a systematical fatigue test programme carried out to verify fatigue properties of CrNiMo(V) steels quenched and tempered to 800 1000 MPa strength. A valuable set of fatigue failures from the high lifetime area was acquired.Microfractographical analysis of these failures enabled to evaluate critically the influence of inclusions, their dimensions, character and morphology on the initiation and propagation of the fatigue cracks in the area of fatigue strength. Comparison...
Computational Fatigue Damage Prediction of the Lorry Frames under Random Excitation
Milan Vasko, Milan Saga, Bohus Leitner
Communications - Scientific Letters of the University of Zilina 2010, 12(4):62-67 | DOI: 10.26552/com.C.2010.4.62-67
The paper deals with FEM application in the TATRA 815 lorry frame construction fatigue life estimation. Construction of critical nodes from the fatigue damage point of view was found and analyzed. Analysis of the particular traffic state influence on the fatigue damage cumulation will be presented too.
Conditions of Stress Corrosion Crack Growth and Retardation in X70 Steel in Carbonate Environments
Ivo Cerny, Dagmar Mikulova, Pavel Novak
Communications - Scientific Letters of the University of Zilina 2010, 12(4):68-72 | DOI: 10.26552/com.C.2010.4.68-72
X70 steel has been often used for building of high pressure transit pipelines. In spite of multiple pipeline protection being used, namely insulation and cathodic protection, in complicated soil and environmental conditions, some pipeline sections can be exposed to corrosive environments. Seriousness of stress corrosion cracking (SCC) damage in carbonate environments is being sometimes flouted by some operators. The work was aimed at qualitative and quantitative analyses of SCC process and damage mechanisms under static loading with individual unloading cycles in standard carbonate solution at room and elevated temperatures. SCC growth was demonstrated...
Some Computational Aspects of Vehicle Shell Frames Optimization Subjected to Fatigue Life
Milan Saga, Peter Kopas, Milan Vasko
Communications - Scientific Letters of the University of Zilina 2010, 12(4):73-79 | DOI: 10.26552/com.C.2010.4.73-79
The paper deals with the implementation of the fatigue damage conditions into structural optimization process. The study considers a shell finite element structural analysis in conjunction with the multiaxial rainflow counting, the fatigue damage prediction and naturally the sizing (element thickness) optimizing design. We will analyze FE models under random excitation in time domain. The presented optimizing approach will be implemented into solution program compiled in Matlab.
Corrosion Resistance of Ti6Al4V Titanium Alloy with Modified Surfaces
Lenka Skublova, Viktor Skorik, Rastislava Mrazikova, Branislav Hadzima
Communications - Scientific Letters of the University of Zilina 2010, 12(4):80-84 | DOI: 10.26552/com.C.2010.4.80-84
Corrosion behaviour of biocompatible Ti6Al4V titanium alloy has been investigated by using electrochemical impedance spectroscopy in Hank's physiological solution for two modified states of titanium surface. On the basic of type and shape of Nyquist curves obtained from EIS measurements probable mechanisms of corrosion in a specific corrosion system are assigned.
Rheological Properties of Acrylic Bone Cement Smartset HV
Henrietta Lelovics, Tatiana Liptakova
Communications - Scientific Letters of the University of Zilina 2010, 12(4):85-89 | DOI: 10.26552/com.C.2010.4.85-89
The rheological behaviour of polymethylmethacrylate bone cement SmartSet® HV prepared by hand and vacuum mixing was characterized using an oscillatory rheometer. Complex viscosity, damping factor, loss and storage modulus were measured by dynamic mechanical thermal analysis (DMTA) after several periods of ageing as a function of temperature for a range of 22-70 °C. Time-dependent changes of measured parameters were observed which were partially influenced by the cement preparation method.
Phase Analysis of Nickel Superalloy Inconel 738 LC
Zdenek Jonsta, Petr Jonsta, Katerina Konecna, Miriam Gabcova
Communications - Scientific Letters of the University of Zilina 2010, 12(4):90-94 | DOI: 10.26552/com.C.2010.4.90-94
Alloys of INCONEL (hereinafter IN) type play an important role among superalloys, used for the components of aircraft engines, gas turbinesand turbo blowers. It is cast material which is alloyed in a complex manner on the Cr-Al-Mo-Ti-Nb-Zr basis.The presented work made a detailed microstructural analysis of cast nickel superalloy IN 738 LC after heat treatment to the required quality and after long term annealing at the temperature of 850 °C and at dwell of 100, 500, 1000, 5000 and 10 000 hours.Higher level of alloying of this alloy shows the higher level of a segregation activity. This may lead to high temperature exploitation to the development of...
Evolution of the Fe-Rich Phases in Recycled AlSi9Cu3 Cast Alloy during Solution Treatment
Eva Tillova, Maria Chalupova, Lenka Hurtalova
Communications - Scientific Letters of the University of Zilina 2010, 12(4):95-101 | DOI: 10.26552/com.C.2010.4.95-101
Using recycled aluminium cast alloys is profitable in many aspects. Requiring only 5% of the energy to produce secondary metal as compared to primary metal and generates only 4% of the CO2 emissions, the recycling of aluminium is therefore beneficial of both environmental and economical point of view. AlSi9Cu3 is a very frequently employed die-casting alloy. It is used in almost all fields of pressure die casting, especially in the fabrication various motor mounts, pistons, cylinder heads, heat exchangers, air conditioners or gearings. Al-Si-Cu alloys usually contain Cu and sometimes Mg as the main alloying elements, together with various impurities...