Communications - Scientific Letters of the University of Zilina, 2006 (vol. 8), issue 4
Articles
Mechanisms of the Early Fatigue Damage in Metallic Materials
Jaroslav Polak, Jiri Man, Martin Petrenec
Communications - Scientific Letters of the University of Zilina 2006, 8(4):5-9 | DOI: 10.26552/com.C.2006.4.5-9 
The early stages of the fatigue damage in f.c.c. and b.c.c. metals are studied using high resolution techniques. The localization of the cyclic plastic strain results in formation persistent slip bands (PSBs) with specific dislocation structure. Characteristic surface relief is formed at locations where PSBs emerge on the surface. It consists of extrusions and intrusions separated by the original flat surface. Atomic force microscopy is used to study the details of the surface relief. The experimental findings are discussed in terms of the point defect model of fatigue crack initiation.
Quantitative Fractography - Well Spring of Intimate Knowledge in Fatigue Crack Growth History
Jiri Kunz, Jan Siegl, Ivan Nedbal
Communications - Scientific Letters of the University of Zilina 2006, 8(4):10-14 | DOI: 10.26552/com.C.2006.4.10-14
Quantitative fractography of fatigued structure parts can offer very useful and valuable information on the fatigue process. One of main contribution of this experimental method is a detailed description of fatigue crack growth in time and in space. The fractographic reconstitution of fatigue process history is conditioned by the existence and detectability of a fractographic feature characteristics of which is correlated with the fatigue crack growth rate. In the paper presented, three various fractographic features are used for the fractographic reconstitution - striations (in the case of constant amplitude loading), beach marks (for simple program...
Thermal and Mechanical Fatigue in a Qe22 Magnesium Alloy Reinforced with Short Saffil Fibres
Zuzanka Trojanova, Pavel Lukac
Communications - Scientific Letters of the University of Zilina 2006, 8(4):15-20 | DOI: 10.26552/com.C.2006.4.15-20
Using non-destructive methods changes in the microstructure of QE22 metal matrix composites (MMC) due to thermal and mechanical cycling have been investigated. Thermal stresses induced in composites due to a considerable difference between thermal expansion coefficients of the matrix and ceramic reinforcement may create new dislocations on cooling from elevated to ambient temperature. Thermal stresses can achieve the yield stress of the matrix and micro-glide of newly created dislocations as well as their annihilation can occur. Thermodynamic processes in the matrix influence these effects.
An Effect of Microstructure Defects on Fatigue Resistance of Glass Fibre Reinforced Polymer Composites Used for Springs of Freight Vehicles
Ivo Cerny, Rayner M. Mayer, Ivan Furbacher
Communications - Scientific Letters of the University of Zilina 2006, 8(4):21-24 | DOI: 10.26552/com.C.2006.4.21-24
Fatigue properties of glass reinforced polymer (GRP) composite materials and advanced components manufactured using GRP are discussed with an emphasis on scale and microstructure effects. Results of an experimental investigation of fatigue damage mechanisms under bending and shear cyclic loading and effects of microstructural defects resulting from an insufficient resin wet out are presented and analysed. It was shown that if microstructural defects are present in the component, initiation of fatigue damage is localised into these areas, resulting in sudden, premature failure. Fatigue life can be then reduced by more than three orders in comparison...
Constraint Aspects of the Evaluation of Fatigue Test Results in Paris Region
Zdenek Knesl, Pavel Hutar, Stanislav Seitl
Communications - Scientific Letters of the University of Zilina 2006, 8(4):25-28 | DOI: 10.26552/com.C.2006.4.25-28
The growth of the fatigue crack is dependent on the crack growth resistance of the material as a bulk property. The fatigue crack growth properties of a material are usually described by the correlation between a crack propagation rate, and a corresponding range of the stress intensity factor (Paris-Erdogan law). Formulated modified Paris-Erdogan law estimates quantitatively the changes of the fatigue crack propagation rate due to different level of constraint. In-plain constraint was described by T-stress value. The validity of the approach suggested has been proved by the comparison of measured and calculated values of the crack propagation rate...
Comparison of a New Equation Describing Fatigue Crack Growth Curves with the Nasgro Equation
Jan Kohout, Stanislav Vechet, Vojtech Hruby
Communications - Scientific Letters of the University of Zilina 2006, 8(4):29-33 | DOI: 10.26552/com.C.2006.4.29-33
The so-called NASGRO equation allows a very good description of fatigue crack growth curves, i.e. the dependence of crack length increase per one fatigue cycle da/dN on the stress intensity factor range K. In 1999 the first author of this paper published quite similar equation, which written for given loading cycle asymmetry with positive stress ratio R contains the same parameters having similar meaning as in the NASGRO equation. In most cases studied by the authors this equation leads to a better fit than the NASGRO equation, above all when the experimental curve contains relatively long Paris straight line and/or relatively sharp bend from this...
Influence of Technological Factors on Fatigue Properties of Steel Sheets
Marian Bursak, Otakar Bokuvka
Communications - Scientific Letters of the University of Zilina 2006, 8(4):34-37 | DOI: 10.26552/com.C.2006.4.34-37
Treatment technology can influence the fatigue process positively or negatively. The paper analyzes the influence of cold levelling of strips from coils of steel grade E 700 TS (Re 700 MPa) on the fatigue crack initiation and the fatigue limit under one-sided bending (R 0.1). It indicates a positive effect on the above-mentioned characteristics if strips are loaded under one-sided bending from the side where residual compressive stress is formed during levelling.By blasting a sheet made of steel grade 11 375.1, the fatigue limit under symmetrical flat bending was increased due to the hardening and formation of residual compressive stress. The paper...
Influence of Atmospheric Corrosion on the Service Life of Steel Sheets
Marian Bursak, Jan Michel
Communications - Scientific Letters of the University of Zilina 2006, 8(4):38-41 | DOI: 10.26552/com.C.2006.4.38-41
The paper analyses the influence of the duration of atmospheric corrosion on basic mechanical and fatigue properties of steel sheet 2.16-4.46 mm thick, made of low-carbon steel with higher atmospheric corrosion resistance. A decrease of mechanical properties as a function of the exposure time is mainly due to a weight loss and the fatigue limit decrease under flat bending is due to increased surface roughness weathering steel too. The fatigue limit is a crucial characteristic for the service life of products, since after 5 years of exposure it decreased by 36%, while the ultimate tensile strength decreased by as little as 8%.
Fatigue Behaviour of Nodular Cast Iron at Various Loading Cycle Asymmetry
Stanislav Vechet, Jan Kohout, Klara Hanzlikova, Vojtech Hruby
Communications - Scientific Letters of the University of Zilina 2006, 8(4):42-46 | DOI: 10.26552/com.C.2006.4.42-46
Fatigue behaviour of nodular cast irons is described in specialized literature quite well but the majority of fatigue tests in high cycle region has been made at symmetrical bending or at symmetrical tension-compression loading. The role of loading cycle asymmetry is very important because the fatigue limit of nodular cast irons is substantially influenced by mean static stress. Unfortunately, the number of papers describing the influence of mean static stress is quite low. The aim of the presented paper consists in presenting the results of long-term research of nodular cast irons at high cycle region at different loading cycle asymmetry. Several...
The Relation between Microstructure Composition and Fatigue Properties of ADI
Klara Hanzlikova, Stanislav Vechet, Jan Kohout
Communications - Scientific Letters of the University of Zilina 2006, 8(4):47-50 | DOI: 10.26552/com.C.2006.4.47-50
The presented work deals with a high-strength variant of nodular cast iron, so-called ADI (austempered ductile iron). This material ranks among prospective structural materials and is more and more applied in all important branches of machine industry. Recently it has even been applied to castings for cyclically loaded components, i.e. gears and traversing wheels, crankshafts of motor-cars, vans and trucks, swivel pins, rail brakes, pressure pipes in oil industry etc. The microstructure composition of an ADI matrix consists especially of bainitic ferrite and stabilized austenite. However, in dependence on transformation dwell some amount of martensite...
Influence of Annealing on Structure and Fatigue Properties of Microalloyed Steel
Gejza Rosenberg
Communications - Scientific Letters of the University of Zilina 2006, 8(4):51-56 | DOI: 10.26552/com.C.2006.4.51-56
Advanced microalloyed steels (HSLA steels) contain microstructural components whose mechanical properties can be altered by exposure to elevated temperatures, for example, in application of welding cycles. The objective of this paper is to identify the relative influence of annealing (annealing at 650°C for 25 min) on microstructure and fatigue properties variability of HSLA steels. The results obtained in this work suggest that in spite of no or very small positive effect of annealing on the fatigue limit of HSLA steels with no stress concentrator in its presence it can be expected that the annealing has a negative influence either on fatigue crack...
A New Approach to the Interpretation of Signals from Temperature Sensors
Milan Blagojevic, Dejan Petkovic
Communications - Scientific Letters of the University of Zilina 2006, 8(4):57-60 | DOI: 10.26552/com.C.2006.4.57-60
A basic approach in adaptive modeling of data acquisition is based on the comparison of real time data with the data previously predicted from the adequate numerical model. Our research was initiated to find a better algorithm for prediction of fire growth in enclosed spaces by means of interpretation of signals from fire sensors. The data obtained from temperature sensors are compared in a real time with predicted data and are used to adjust the numerical model for prediction so that it matches the reality. This adaptive approach has the following primary goals: early warning of fire growth, better alarm decision making, realization of an adaptive...
Communications: The Way of Ransmitting Messages and Communication Skill
Zoran Cekerevac, Slobodan Ristic
Communications - Scientific Letters of the University of Zilina 2006, 8(4):61-65 | DOI: 10.26552/com.C.2006.4.61-65
Communication is woven in almost all branches of economy and art, either as a separate skill or as one of the segments in the interdisciplinary approach. It is also a demonstrative and irreplaceable link in the study of various disciplines of management and marketing, as well as in public relations. This paper, after a short basic characteristic of communication, gives detailed analysis about the way of transmitting messages and communication skill. Special attention was paid to the understanding of the sender and the recipient, through the process of coding and decoding of the information. At the end, a communication network established by combining...