MATERIALS ENGINEERING, Vol. 19 (2012), No. 3

CONTENTS and ABSTRACTS

Đorđević, M., Aleksandrović, S., Vujinović, T., Stefanović, M., Lazić, V., Nikolić, R. (pp. 88-94)
COMPUTER CONTROLLED EXPERIMENTAL DEVICE FOR INVESTIGATIONS OF TRIBOLOGICAL INFLUENCES IN SHEET METAL FORMING Full text (PDF 934 kB) - Available online 03 May 2012
Sheet metal forming, especially deep drawing process is influenced by many factors. Blank holding force and drawbead displacement are two of them that can be controlled during the forming process. For this purpose, an electro-hydraulic computerized sheet-metal strip sliding device has been constructed. The basic characteristic of this device is realization of variable contact pressure and drawbead height as functions of time or stripe displacement. There are both, pressure and drawbead, ten linear and nonlinear functions. Additional features consist of the ability to measure drawing force, contact pressure, drawbead displacement etc.
The device overview and first results of steel sheet stripe sliding over rounded drawbead are presented in the paper.






Mutavdžić, M., Lazić, V., Milosavljević, D., Aleksandrović, S., Nikolić, R.R., Čukić, R., Bogdanović, G. (pp. 95-103)
DETERMINATION OF THE OPTIMAL TEMPERING TEMPERATURE IN HARD FACING OF THE FORGING DIES Full text (PDF 729 kB) - Available online 22 June 2012
Here is analyzed selection of the optimal technology for heat treatment during the reparation of the damaged forging dies. Those tools are manufactured from alloyed tool steels for operation at elevated temperatures. Those steels are prone to self-hardening, so in reparatory hard-facing they must be preheated, additionally heated and tempered. During the tempering, in temperature interval 500-600°C, a secondary increase of hardness and decrease of impact toughness occurs, the so-called reversible tempering brittleness. Here is shown that it can be avoided by application of metallurgical and technological measures. Metallurgical measures assume adequate selection of steels. Since the considered steels are per se prone to tempering brittleness, we conducted experimental investigations to define the technological measures to avoid it. Tests on models were conducted: tempering from different temperatures, slow heating and cooling in still air. Hardness measurements showed that at 520°C, the secondary increase of hardness occurs, with drop of the impact toughness. Additional hard-facing tests included samples tempered at various regimes. Samples were prepared for mechanical and metallographic investigations. Results presented illustrate influence of additional heat treatment on structure, hardness and mechanical properties of the hard-faced layers. This enabled establishing the possibility of avoiding the tempering brittleness through technological measures.





Kokavec, M., Konečná, R., Nicoletto, G. (pp. 104-109)
NODULAR CAST IRON FATIGUE LIFETIME IN CYCLIC PLANE BENDING Full text (PDF 790 kB) - Available online 25 June 2012
The fatigue behavior of a component is strongly dependent also on the material and its surface condition. Therefore, the manner in which the surface is prepared during component manufacturing (surface roughness, residual stresses etc.) has a decisive role in dictating the initiation time for fatigue cracks. The fatigue behavior of the same material, a nodular cast iron, with three different surface conditions (fine ground, sand blasted and as-cast) has been investigated under cyclic plane bending. The results show differences in fatigue strength, which are associated with the surface conditions. The characteristics of the surface layers of the different test specimens were examined by metallography.





Kumar, S., Ratol, J.S. (pp. 110-116)
EXPERIMENTAL INVESTIGATION OF EROSIVE WEAR ON THE HIGH CHROME CAST IRON IMPELLER OF SLURRY DISPOSAL PUMP USING RESPONSE SURFACE METHODOLOGY Full text (PDF 361 kB) - Available online 7 July 2012
Erosive wear occurs on the impeller and volute casing of the slurry disposal pump due to the impact of the ash particles on the impeller with a high velocity. Due to erosive wear, pump life become very short. The service life of centrifugal pump, handling slurry can be increased by reducing the erosive wear.
In the present work, the experimental investigation of erosive wear has been carried out on the high speed slurry erosion tester to understand the effects of the ash concentration in slurry, rotational speed of the pump impeller and ash particle size on erosive wear. The erosive wear behaviour of high chrome cast iron was investigated by Response surface methodology (RSM). Analysis of variance (ANOVA) was used for statistical analysis and the modeled values for the response were obtained with the help of modeled equation. The result shows that the ash concentration in slurry and kinetic energy of the moving particles highly contributes to erosive wear of pump impeller as compared to the ash particle size.






Guagliano, M., Trško, L., Bokůvka, O., Nový, F. (pp. 117-123)
INFLUENCE OF SHOT PEENING ON AISI 316Ti FATIGUE PROPERTIES Full text (PDF 496 kB) - Available online 1 September 2012
This paper deals with examination of fatigue properties of AISI 316Ti stainless steel before and after shot peening including analysis of residual stress relaxation during rotating bending fatigue tests (f = 50 Hz, T = 20 ± 3 °C, R = - 1) with use of X - ray diffractometer. Obtained experimental results show increase of fatigue properties in the high – cycle region including fatigue limit and show the behavior of residual stress at cyclic loading in the region from N = 103 cycles to N = 107 cycles of loading.





Krmela, J., Beneš, L., Krmelová V. (pp. 124-135)
STATICAL EXPERIMENTS OF TIRE AS COMPLEX LONG-FIBRE COMPOSITE FOR OBTAINING MATERIAL PARAMETERS AND DEFORMATION CHARACTERISTICS Full text (PDF 496 kB) - Available online 5 September 2012
The article deals with the statical experiments of tires for obtaining material parameters and deformation characteristics by tensile testing machine and also special statical testing tire machine. The tires consist of polymer matrix – rubber and long-filament reinforcement – cords, hence the tires are fall within as very complex long-fibre composite with specific deformation characteristics. These tire deformation characteristics have given geometry shape of tire and material parameters of component parts of tire-casing. Nowadays the computational modeling is used for tire solutions and experiments are subsidiary only. But the combination of computational modeling with experimental approach is necessary to use for prediction real states of tires. For computational modeling of tires the material parameters of each component part of tire-casing are necessary as material input data for computational models. These material parameters can be obtained by tensile test by statical testing machine. The geometry parameters of multi-layer test specimens of steel-cord belt with conditions of tensile tests are designed. The data from statical deformation characteristics are necessary for comparison of computational outputs with experimental data. The special testing tire machine called statical adhesor is used to obtain deformation characteristics and information abohes with pressure distribution in contact patches. The experimental results of chosen radial tire 245/40 R18 for passenger car are presented in this article. In this paper a new formula for calculating of value of radial stiffness is designed too.







© University of Žilina, Faculty of Mechanical Engineering, ISSN 1335-0803