Communications - Scientific Letters of the University of Zilina, 2004 (vol. 6), issue 2
Articles
Theoretical Strength of Solids
Jaroslav Pokluda
Communications - Scientific Letters of the University of Zilina 2004, 6(2):5-11 | DOI: 10.26552/com.C.2004.2.5-11 
The significance of theoretical strength (TS) investigations is explained and a brief overview of the current state of TS calculations is presented on the background of a historical evolution. Influence of crystal defects on TS is outlined by taking into account published theoretical models. The study is completed by a discussion concerning differences between theoretical and experimental results.
Fatigue Properties of ADI in Dependence on Isothermal Transformation DWELL
Stanislav Vechet, Jan Kohout, Klara Hanzlikova
Communications - Scientific Letters of the University of Zilina 2004, 6(2):12-15 | DOI: 10.26552/com.C.2004.2.12-15
As a result of excellent both mechanical and technological properties, austempered ductile iron (ADI) is ranked with very perspective structural materials. Recently it has been applied even to castings for dynamically loaded components and a considerable part of ADI production is applied also in military industry. The structure of ADI matrix, mostly created by the mixture of bainite and stabilized austenite, strongly depends on transformation conditions, i.e. temperature and the length of isothermal transformation dwell. An ADI transformed at 380 °C during a temporal range from 2 minutes to 9 hours was studied in details, with emphasis on structural...
Local Elastic Stress Approach for Fatigue Life Calculation by the Finite Element Method (FEM)
Milan Ruzicka
Communications - Scientific Letters of the University of Zilina 2004, 6(2):16-21 | DOI: 10.26552/com.C.2004.2.16-21
The paper discusses possibilities of a description of material fatigue and prediction of service life of machine parts on the basis of stress state calculations using the finite element method (FEM). It focuses on the local approach to the assessment of service life that is based on the determination of elastic stress peaks in stress raisers (notches) and on the derivation of the fatigue stress curves for assessed structural points. The method of taking into account the stress concentration and stress gradient during the determination of synthetic fatigue curves is described. Furthermore, methods of processing the loading history and correcting mean...
Behaviour of 14 109 Bearing Steel
Marian Cincala
Communications - Scientific Letters of the University of Zilina 2004, 6(2):22-25 | DOI: 10.26552/com.C.2004.2.22-25
Fatigue lifetime of 14 109 bearing steel in a high-cycle region in tension-compression has been studied experimentally. The aim was to determine the SN curve including fatigue limit, to perform fractographic observation and to analyze crack initiation sites, to discuss the large scatter of lifetime data, which is inherent to high strength steels, and to check the empirical area method to predict fatigue limit for this type of steel.
Mechanical Properties of Az91 Magnesium Alloys
Pavel Lukac, Zuzanka Trojanova
Communications - Scientific Letters of the University of Zilina 2004, 6(2):26-29 | DOI: 10.26552/com.C.2004.2.26-29
Commercial magnesium alloys AZ91 were reinforced with Al2O3 short fibres. The composites were prepared by different fabrication routs (powder metallurgy technique, squeeze casting and casting followed by extrusion). Some specimens of the AZ91 alloy were prepared using equal channel angular pressing. The values of the yield stress and the maximum stress of specimens deformed at temperatures between 20 and 300 °C were determined. The test temperature strongly influences the mechanical properties of the AZ91 alloy and its composites.
Thermophysical Properties of Copper - Carbon Fibre Composite
Pavol Sebo, Pavol Stefanik
Communications - Scientific Letters of the University of Zilina 2004, 6(2):30-33 | DOI: 10.26552/com.C.2004.2.30-33
In this paper two main properties of copper matrix - carbon fibre composite from the point of view of using it in electronics as a material able to dissipate the heat are presented. Thermal expansion and thermal conductivity of the composite can be changed in dependence on volume amount of fibres in composite, their geometrical arrangement and on the properties of carbon fibres. Propagation of heat across the composite was measured. Results are in good agreement with those obtained by finite elements method calculation.
Influence of the Strain Rate on the Notch Toughness of Cold-Forming Steels
Jan Michel, Marian Bursak
Communications - Scientific Letters of the University of Zilina 2004, 6(2):34-36 | DOI: 10.26552/com.C.2004.2.34-36
The paper analyses the influence of the strain rate with loading rates of 1.7.105 4.8 m.s1 on the notch toughness of hot-rolled microalloyed steels S 315 MC and S 460 MC and cold-rolled deep-drawing steels DC 06, H 220 B and H 220 P. It discusses a possibility of utilising a modified notched-bar impact test to predict the formability of these steels at high strain rates of thin steel sheets.
The Study of Material Changes in Shot Blasting Process
Dusan Kniewald, Janette Brezinova, Anna Guzanova
Communications - Scientific Letters of the University of Zilina 2004, 6(2):37-42 | DOI: 10.26552/com.C.2004.2.37-42
The contribution deals with the blasting process from the point of view of degradation phenomena. The interaction of blasting material with the blasted surface causes changes in both blasting material and substrate. In this paper we investigate the wear of various blasting materials and the degradation of the substrate surface. On the basis of the evaluation of studied phenomena in blasting process the classification of upgrading and degrading effects was carried out.
Correlation of Fracture Surface Topography and Transition Behavior of Nodular Cast Iron
Gianni Nicoletto, Radomila Konecna
Communications - Scientific Letters of the University of Zilina 2004, 6(2):43-48 | DOI: 10.26552/com.C.2004.2.43-48
Dynamic testing methods, especially the Charpy V-notch testing at different temperatures, are commonly used to determine the impact response of metallic materials. However, in nodular cast iron this transition trend is characterized by scatter, which makes it difficult to precisely identify the influence of microstructural features on material response. In this paper the vertical surface roughness parameter RV obtained from fracture profiles is considered on the hypothesis that the surface topography is a sensitive indicator of the energy absorbed by plastic deformation and of the microstructure. Nodular cast irons having a range of microstructures...
Calculation of the Equivalent Conicity Function of the Railway Wheelset Tread Profile at the Delta R Function with a Negative
Juraj Gerlici, Tomas Lack, Marta Kadorova
Communications - Scientific Letters of the University of Zilina 2004, 6(2):49-56 | DOI: 10.26552/com.C.2004.2.49-56
The rail-wheel interface is fundamental to explain the dynamic running behaviour of a railway vehicle. It must therefore be understood and among the parameters by which it is characterised, the one called "equivalent conicity" plays an essential role since it allows the satisfactory appreciation of the wheel-rail contact on tangent track and on large-radius curves.By definition, the equivalent conicity is equal to the tangent of the cone angle tg e of a wheelset with coned wheels whose lateral movement has the same kinematic wavelength as the given wheelset.In order to be able to compare the results obtained by different railways, both as to the value...
Designing of Retaining Structures of Reinforced Soil with Limit Conditions Method
Edward Hutnik, Andrzej Surowiecki
Communications - Scientific Letters of the University of Zilina 2004, 6(2):57-61 | DOI: 10.26552/com.C.2004.2.57-61
The principles of limit conditions method in designing modern retaining structures of reinforced soil are presented. The principles are elaborated according to French Standard NF P 94-200 [1, 3]. Procedures of checking of particular kinds of stability are described. The most frequently adopted combinations of loads are given together with partial factors of safety of external, internal and general stability, method factors, friction factors of soil medium-reinforcement and values of partial safety factors of settlement.