MATERIALS ENGINEERING, Vol. 19 (2012), No. 4

CONTENTS and ABSTRACTS

Vehovszky, B., Cziráki, Á. (pp. 136-148)
COMPUTER CONTROLLED INVESTIGATION OF SURFACE AND BULK PROCESSES IN MG-BASED ALLOYS DURING HYDROGEN ABSORPTION Full text (PDF 1821 kB) - Available online 30 September 2012
Different Mg-based alloys were tailored and prepared to investigate the surface and bulk processes during hydrogen absorption. Volumetric-, resistance-, XRD-, optical-, and mass measurements were carried out. Heat treatment experiments showed that the short-term thermal stability limits (during heating up at 5 K/min) of the amorphous samples were between 125-175 ° C, while long-term stability (during 24h heat treatment) is always lower – between 80 and 150°C. Nanocrystalline alloys were stable up to 300°C. Hydrogen absorption measurements were executed between 25 and 300°C. Pd-containing alloys were found to be the fastest absorbers, and 200°C was the optimal temperature regarding absorption rate. Etching the samples previously in HF solution enhances absorption by inducing surface cracking. This phenomenon was thoroughly examined by optical microscopy. The effect of hydrogen on the crystallization properties of MgNiPd sample was determined via in-situ resistance measurements.





Schmidova, E., Hanus, P. (pp. 149-156)
STRUCTURAL DEGRADATION OF HETEROGENEOUS WELDED JOINTS Full text (PDF 592 kB) - Available online 5 October 2012
Developing the techniques of welding materials with higher dynamic strength onto the rolling surfaces of rails is one of the options for increasing their operational endurance. The subject of this paper is an analysis of heterogeneous weld joints experimentally manufactured by welding medium-carbon austenitic steels onto high-carbon unalloyed pearlitic steels. The analyses focus on examinations of the marginal mixing of the materials at the fusion line and the circumstances under which intercrystalline cracks form in the weld deposit layers. Structural analyses, chemical microanalyses and a hardness assessment were performed in order to identify the corresponding structural changes. The proportion of zonal vs. interdendritic segregation of the alloying elements in the degradation of the welded joint was distinguished. We described the nature of the structural heterogeneities produced, locally connected with the martensitic transformation. The chemical heterogeneity leading to the formation of martensite at grain boundaries was identified as the limiting effect.





Krynke, M., Selejdak, J., Borkowski, S. (pp. 157-163)
THE QUALITY OF MATERIALS APPLIED FOR SLEWING BEARING RACEWAY – TECHNICAL PAPER Full text (PDF 794 kB) - Available online 8 October 2012
Selected slewing bearings and their application have been described in this article. Basic causes of the damage pitch surfaces of slewing bearings have been analyzed and examples of the damage have been presented as well. Special attention was paid to these kinds of damage which appeared most often in the case of the pitch surfaces of the bearings and those ones which very often cause premature exchange of the bearing and its scrapping. On the basis of the conducted studies it was stated that the main cause of the damage to the pitch surfaces of the bearings is the excessive load of rolling elements. Based on the results of the conducted analysis, actions limiting the occurrence of the damage to the pitch surfaces of the bearings, which lead to their premature exchange, have been proposed. One of the suggested actions, limiting the premature exchange of bearings, is the necessity of exceptionally thorough design and selection of the slewing bearings, including the conditions of their foundation.





Bauernhuber, A., Markovits, T. (pp. 164-174)
INVESTIGATING THE JOINING OF PMMA PLASTIC TO STEEL BY Nd:YAG LASER Full text (PDF 728 kB) - Available online 16 October 2012
Due to the effort of weight reduction in the manufacturing of vehicles, the application and therefore the joining of different materials such as plastics and metals plays more and more important role in the development of the joining processes nowadays. In this research work, the joining of PMMA plastic sheets and unalloyed steel pins was investigated. The authors applied Nd:YAG laser beam to create the bond, and tensile tests were carried out to analyse how the strength of the joint is influenced by the heating time, the penetration depth of the steel workpieces in the plastic and the surface roughness of steel. The observed bubble formation and the tearing characteristics were also studied.





Halas, O., Švanda, P. (pp. 175-182)
STUDY ON PHYSICAL - MECHANICAL PROPERTIES OF ALKALI ACTIVATED MATERIALS BASED ON FLY ASH Full text (PDF 541 kB) - Available online 5 November 2012
Alkali activated materials are relatively new materials, thanks to their good mechanical, physical, thermal properties and at the same time environmental friendliness, they could be widely adopted in different fields. The experiments, described in this article, are focused on the investigation of some basic mechanical-physical properties of alkali activated materials based on fly ash. For the following experiments were prepared two types of samples: in form of cubes and beams. On the cubes was tested compressive strength and on the beams – bending tensile strength and Young’s modulus of the material. It was also investigated the influence of water glass modulus, temperature of heat treatment on the final strength of the samples.





Vojsovičová, M., Liptáková, T. (pp. 183-188)
CHANGES OF RHEOLOGICAL PARAMETERS OF POLYPROPYLENE AND POLYETHYLENE AFTER EXPOSURE IN ALIPHATIC n-HEXANE Full text (PDF 330 kB) - Available online 7 November 2012
Rheological properties of thermoplastic polymer materials before and after exposure to a chemical solution were evaluated using the frequency sweep test, which monitors changes in viscoelastic properties of polymers with respect to their molecular structure and their behavior in thermoplastic processing. As experimental material thermoplastic polyethylene and polypropylene samples were used and subjected to influence of n hexane solution for period of 3 and 6 months. Measurements were performed using oscillating rheometer Physica Rheometer MCR301 and carried out at the temperatures of 160 °C and 80 °C. Degradation process resulted in changes of complex dynamic viscosity, storage and loss modulus, changes in molar mass and its distribution which sufficiently prove the rheological changes.







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