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1
Content available Structure of 22Cr25NiWCoCu Austenitic Stainless Steel After Ageing
Sroka Marek, Zieliński A., Puszczało T., Sówka K., Hadzima B.
Archives of Metallurgy and Materials
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2022
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Vol. 67, iss. 1
175--180
EN
The 22Cr25NiWCoCu austenitic stainless steel was developed by AB Sandvik Material Technology in Sweden. Due to its high creep strength and good corrosion resistance, this material is well suited for use in superheaters in advanced coal-fired power boilers as well as in other types of steam boilers using various types of fuel. The examined material was subject to long-term ageing for the time of annealing up to 20 000 h at 700 and 750°C. Precipitation processes and microstructure stability as-received and after ageing were investigated. Examination of the microstructure was conducted using scanning electron microscopy. The identification of secondary phases was carried out by X-ray phase composition. Using the results of the investigations of precipitation processes in the microstructure, both within the grains and at the grain boundaries, their statistical analysis was carried out. To illustrate this impact, the following parameters were used: surface area and equivalent diameter of precipitates. Based on the surface area measurements, the percentage of the phase in the reviewed photo’s total area was calculated.
2
Content available Influence of load and reinforcement content on selected tribological properties of Al/SiC/Gr hybrid composites
Veličković S., Miladinović S., Stojanović B., Nikolić R. R., Hadzima B., Arsić D.
Production Engineering Archives
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2018
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Vol. 18
18--23
EN
Hybrid materials with the metal matrix are important engineering materials due to their outstanding mechanical and tribological properties. Here are presented selected tribological properties of the hybrid composites with the matrix made of aluminum alloy and reinforced by the silicon carbide and graphite particles. The tribological characteristics of such materials are superior to characteristics of the matrix – the aluminum alloy, as well as to characteristics of the classical metal-matrix composites with a single reinforcing material. Those characteristics depend on the volume fractions of the reinforcing components, sizes of the reinforcing particles, as well as on the fabrication process of the hybrid composites. The considered tribological characteristics are the friction coefficient and the wear rate as functions of the load levels and the volume fractions of the graphite and the SiC particles. The wear rate increases with increase of the load and the Gr particles content and with reduction of the SiC particles content. The friction coefficient increases with the load, as well as with the SiC particles content increase.
3
Content available Influence of welding time on quality of the friction welded joint of two dissimilar steels
Ratković N., Lazić V., Arsić D., Nikolić R., Hadzima B.
Zeszyty Naukowe. Quality. Production. Improvement
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2017
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No. 1 (6)
1--11
EN
There are several factors that influence the friction welding (FW) process, i.e. the quality of the welded joint, like the welding time, the contact pressure, the compacting pressure, the friction speed etc. The joining process is additionally complicated if the two different materials are to be welded to each other. The subject of research, presented in this paper, is the welding time of the FW process, since the level of axial and radial plastic deformation of the welded pieces and shortening of the welded part depend mainly on the welding time. The paper first presents some theoretical basics of the FW process and then, in the experimental part, the influence of the process duration is investigated. The two materials that the experimental samples were made of are the high-speed steel and the steel for tempering.
4
Content available The fatigue life estimate by the LEFM concept of the tube joints exposed to axial load
Djoković J. M., Nikolić R. R., Bujňák J., Hadzima B.
Roczniki Inżynierii Budowlanej
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2017
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z. 17
35--41
EN
In the tube joints the crack growth usually appears along the weld’s edge, i.e. at the spot where the chord and the brace are connected. The semi-elliptical crack the most frequently develops from the initial flaw that originated during the welding. The abrupt change in the material’s structure and response to loading are increasing the normal stresses in the lateral tube at certain spots around the crossing of the main and lateral tubes, producing the “hot spot” stress. Sensitivity to fatigue depends on combination of the cyclic loading, initial defects, environmental influences and the “hot spot” stresses which are the result of the tube walls bending during the loading of the structure. The principles of the Linear Elastic Fracture Mechanics (LEFM) are applied in this paper to analysis of the crack propagation behavior of a thin tube joints. Influence of various parameters was investigated individually and independently, and the share of the fatigue crack growth and subsequently the working life of the welded joint were estimated.
5
Content available Revitalization of the damaged machine parts by hard facing as a way of saving funds
Lazic V., Arsic D., Nikolic R., Mutavzic M., Hadzima B.
Production Engineering Archives
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2016
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Vol. 12, No. 3
9--13
EN
The objective of the research, presented in this paper, was to demonstrate the superiority of the hard facing as the revitalization technology of various damaged machine parts. The analysis of the two different revitalization methods of the damaged machine parts is presented – the replacement of the damaged part by the new – spare part and reparation by hard facing. The comparison is done on the example of hard facing and replacing of damaged loader's teeth. The paper presents a method for calculating costs of the two revitalization technologies based on their profitability and their comparison. That method could be applied for similar calculations for any machine part, with smallest or no adjustments. The paper presents a verification of advantage of applying the hard facing as the machine parts reparatory technology with respect to the other revitalization technology. The savings realized by application of hard facing reparation of the loader's teeth reach 73.5 % for one set of teeth and 82.40per annum of the costs for purchasing the new spare parts. The analysis was conducted under an assumption that organization of the maintenance function is at the exceptionally high level so that the purchasing of the new part/repairing of the damaged one is always done in time. This idealized approach was adopted since in that way one obtains the least economic effects of the reparatory technology application with respect to replacing the part with the spare one. In any other case the economic effects would be significantly higher, namely even more positive in favor of the hard facing revitalization technology.
6
Content available remote Full-scale dynamic testing of the corrosion-damaged, steel-truss structure of Old Bridge over the Danube in Bratislava
Benčat J., Hadzima B.
Czasopismo Techniczne. Budownictwo
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2015
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Y. 112, iss. 2-B
217--227
EN
A large number of existing bridges need to be rehabilitated due to increasing traffic and/or loading requirements and also corrosion action. In this paper, a procedure is presented for estimating the ultimate capacity of a steel bridge over the Danube in Bratislava – Old Bridge (built in 1945). The development of a simplified Finite Element Model (FEM ) and basic modal parameter calculations preceded the experimental investigations of the bridge via static and dynamic in-situ loading tests, so that the main assumptions adopted in the FEM were assessed through comparison between measured and predicted dynamic and modal parameters of the bridge structure. The bridge structure computational model was then optimized by structure variables (primarily, steel structure joints mass and corrosion grade) to achieve the minimum differences between the experimental and theoretical results. The calibrated FEM with the optimal combinations of the mentioned variable values were defined and finally used for structure calculations and for strengthening the design of the real bridge structure.
PL
Wiele istniejących mostów musi zostać odnowionych w związku z rosnącym natężeniem ruchu i/lub z powodu wymagań obciążeniowych, a także w skutek działania korozji. W niniejszej pracy przedstawiono procedurę szacowania nośności granicznej stalowego mostu na Dunaju w Bratysławie - Old Bridge (zbudowanego w 1945 r.). Opracowanie uproszczonego modelu MES i podstawowe obliczenia parametrów modalnych poprzedzały badania statyczne i dynamiczne mostu w skali rzeczywistej. W związku z tym główne założenia modelowania MES zostały przyjęte na podstawie porównania między zmierzonymi i przewidywanymi dynamicznymi i modalnymi parametrami konstrukcji mostu. Model obliczeniowy konstrukcji mostu został następnie zoptymalizowany przez parametry konstrukcji (przede wszystkim przez uwzględnienie masy węzłów stalowych, stopnia korozji), aby osiągnąć minimalne różnice między wynikami badań doświadczalnych i teoretycznych. Skalibrowany model MES z optymalnymi kombinacjami wymienionych parametrów został zdefiniowany i wykorzystany do obliczeń i następnie wzmocnienia konstrukcji rzeczywistej mostu.
7
Content available remote Material parameters affecting degradation processes of Al-brasses in pipe systems
Liptáková T., Lovíšek M., Hadzima B., Dundeková S.
Archives of Materials Science and Engineering
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2015
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Vol. 76, nr 1
27--34
EN
Purpose: As construction material of cooling pipe systems there are often used Al-brasses because their high thermal conductivity, mechanical workability and corrosion resistance. In the pipes liquid media of various chemical compositions are flowing by different rates. It means that the material is loaded mechanically also chemically what results in synergy effect on degradation. Susceptibility to corrosion-erosion damage of four Al-brasses manufactured by different producers is investigated because in operation conditions they have different reliability and lifetime. Design/methodology/approach: By studying of their microstructure, surface state, selected mechanical properties and corrosion characteristics the parameters which affected chemicalmechanical degradation were evaluated. Experimental methods are SEM, EDX and spectral analyses, measurement of microhardness and roughness. Findings: By actual obtained results it was identified that in spite of very similar chemical composition differences in mechanical and corrosion behaviour are affected by technology of manufacturing. It can explain their different durability in operating conditions. Research limitations/implications: To identify more precisely the main parameters important for degradation resistance in various flow media the original experimental device is designed and constructed. The device makes possible to test Al-brasses in various flowing media by the same mail at three flowing rates. By long time lasted experiments in the one it is able to simulated operation specification. Results of the device are not presented yet because they are just in progress. Practical implications: Obtained results will be very helpful for choice of Al-brasses for required operation conditions according important properties which were experimentally verified. Originality/value: It means contribution to economy by material saving in operation by available choice and design and construction of original experimental device.
8
Příspěvek ke studiu korozních vlastností hořčíkových slitin
Lásek S., Čižek L., Blahetová M., Hadzima B., Filuš F.
Zeszyty Naukowe. Mechanika / Politechnika Opolska
|
2001
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z. 72
59-62
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