Numeričko predviđanje izobličenja nakon zavarivanja s različnim slijedom zavarivanja i spajanja

Welding simulation of a test cover for hydropower plant was made due to very large dimensions of the cover. The main aim was to predict distortion after welding in order to avoid machining the cover. Welding process was simulated with the Sysweld program to keep distortion in desired limits. Various welding sequences and clamping conditions were calculated to reduce the distortion. Calculation of microstructure constituents in virtual complex geometry of joints was also analyzed.Simulacija zavarivanja testnog pokrova hidroelektrane provedena je zbog velikih dimenzija ispitne prevlake. Osnovni je cilj predvidjeti izobličenje nakon zavarivanja. Radi postizanja veličine izobličenja u željenim granicama proces zavarivanja je simuliran programom Sysweld. Različiti tijekovi zavarivanja i uvjeta spajanja prorač unati su radi smanjenja izobličenja. Određivanje mikrostrukturnih konstituenata u virtualnoj komleksnoj geometriji spojeva je također provedeno

Unutarnja oksidacija Cu-Se legura

The purpose of our investigation was to perform the thermodynamic calculation of all possible reactions in the Cu-Se-O system and to explain the oxidation mechanism in various conditions. For such study, a model of copper with one single inclusion and alloy with 1.65 wt. % Se were made. Depending on time, the oxidation has been taking place at two different temperatures and two oxygen partial pressures. The oxidized samples have been investigated by DTA, optical and electron microscopy (SEM).Namjena istraživanja je izraditi termodinamički proračun svih mogućih reakcija u sustavu Cu-Se-O i obrazložiti mehanizme oksidacije u različitim uvjetima. Za takovo izučavanje izrađen je model bakra sa samo jednim uključkom i legura sa 1,65 mas. % Se. U ovisnosti od vremena, oksidacija se odvijala kod različitih temperatura i kod dviju različitih djelomičnih tlakova kisika. Oksidirani uzorci su bili ispitivani metodom DTA, optičkom i elektronskom mikroskopijom (SEM)

Utjecaj usitnjavanja zrna i modifikacije eutektičke faze na stezanje pri skrućivanju AlSi9Cu3 legure

Paper describes influence of grain refining and of modification on feeding behavior of Al – alloys. Research was made with the AlSi9Cu3 alloy. Three samples of basic, grain refined, and modified alloy were cast by the newly developed method for determining susceptibility to shrinkage and into the Quick cup measuring cells for simple thermal analyses which were simultaneously done with all these samples. Castings were then analyzed with X-raying, density measurements, visually observed and metallographically examined. Also grain size was determined with light microscopy and polarized light.Ovaj rad opisuje utjecaj dodatka cjepiva i modifikatora na ponašanje napajanja Al-legura. Istraživanja su provedena na AlSi9Cu3 leguri. Tri su uzorka, iz osnovne legure, cijepljene i modificirane, lijevana u „Quick Cup“ mjerne ćelije primjenom novo razvijene metode za određivanje osjetljivosti na stezanje pri skrućivanju. Jednostavna toplinska analiza provedena je simultano u sva tri uzorka. Odljevci su potom ispitani određivanjem gustoće, vizualnom kontrolom i metalografskom analizom. Također, veličina zrna je određena optičkom mikroskopijom u polariziranom svjetlu

Local Squeezing Casting Influence on the Compactness of AlSi10Mg Alloy Castings

The aim of the local squeezing casting process examination has been to eliminate the hot spot i.e. the place of potential formation of shrinkage porosity. The influence of variation of process parameters on the density i.e. soundness (compactness) of AlSi10Mg alloy castings has been obtained by the local squeezing process with the pin during gravity casting in the special permanent mould. Local squeezing parameters have been determined on the basis of preliminary investigations of AlSi10Mg alloy: temperature intervals and relevant temperature of singular phases precipitation and the microstructure development at different cooling rates. The temperature interval of performing the local squeezing casting process have been established in which the density values approaching to the theoretic ones have been determined

Portraits of Complex Networks

We propose a method for characterizing large complex networks by introducing a new matrix structure, unique for a given network, which encodes structural information; provides useful visualization, even for very large networks; and allows for rigorous statistical comparison between networks. Dynamic processes such as percolation can be visualized using animations. Applications to graph theory are discussed, as are generalizations to weighted networks, real-world network similarity testing, and applicability to the graph isomorphism problem.Comment: 6 pages, 9 figure

Unutarnja oksidacija Cu-Se legura

The purpose of our investigation was to perform the thermodynamic calculation of all possible reactions in the Cu-Se-O system and to explain the oxidation mechanism in various conditions. For such study, a model of copper with one single inclusion and alloy with 1.65 wt. % Se were made. Depending on time, the oxidation has been taking place at two different temperatures and two oxygen partial pressures. The oxidized samples have been investigated by DTA, optical and electron microscopy (SEM).Namjena istraživanja je izraditi termodinamički proračun svih mogućih reakcija u sustavu Cu-Se-O i obrazložiti mehanizme oksidacije u različitim uvjetima. Za takovo izučavanje izrađen je model bakra sa samo jednim uključkom i legura sa 1,65 mas. % Se. U ovisnosti od vremena, oksidacija se odvijala kod različitih temperatura i kod dviju različitih djelomičnih tlakova kisika. Oksidirani uzorci su bili ispitivani metodom DTA, optičkom i elektronskom mikroskopijom (SEM)

Influence of cooling rates on temperatures phase transitions and on microstructure of aluminium alloy EN AW-5083

The casting of different forms and dimensions of aluminium alloy EN WA-5083 test samples and the usage of different types of mould materials resulted in achieving different cooling rates of samples. The methods used were simple thermal analysis, using casting into a measuring cell made by the Croning process and using casting into a cone-shaped measuring cell, as well as simultaneous thermal analysis using the method of differential scanning calorimetry. Significant temperature phase transitions and times of solidification were determined, and the dependence model of the solidification time on the sample cooling rate was obtained. Determining the mean number of grains per unit area on samples after having performed the simple thermal analysis and differential scanning calorimetry makes it possible to develop a dependence model of the mean number of grains per unit area on the cooling rate. These models are the basis for carrying out numerical simulations of solidification and microstructure development in the cone-shaped measuring cell, and the comparison of the distribution of the mean number of grains per unit area obtained by simulation with the one obtained experimentally. The obtained results represent a part of the preliminary tests of the microstructure development of industrially cast ingots of EN AW-5083 alloy depending on the local ingot cooling rate.Beim Gießen verschiedener Versuchsmuster mit unterschiedlichen Formen und Grßen der Aluminiumlegierung EN WA-5083 und Verwenden verschiedener Formstofftypen, wurden unterschiedliche Abkhlgeschwindigkeiten festgestellt. Dabei wurde die Methode der einfachen Thermalanalyse angewendet, die beim Gießen in eine Messzelle einmal mit dem Croning-Verfahren hergestellt wurde und einmal in eine kegelfrmige Messzelle gegossen wurde, samt gleichzeitiger Thermalanalyse mit der Methode der differenziertenWrmemessung. Dabei wurden die Temperaturphasen bergnge und Zeiten bis zur Erstarrung ermittelt sowie das Zeit-Modell in Abh ngigkeit der Abkhlgeschwindigkeit bis zur Erstarrung der Versuchsprobe ermittelt. Durch die Bestimmung des Mittelwertes der Anzahl der Krner pro Flche auf der Versuchsprobe nach der durchgefhrten einfachen Thermalanalyse und der Methode der differenziertenWrmemessung, kann ein Abhngigkeitsmodell des Mittelwertes der Anzahl der Krner pro Flche ber die Abk hlgeschwindigkeit erstellt werden. Diese Modelle sind die Basis, um die numerische Simulation des Festwerdens und die Mikrostruktur-Entwicklung in der kegelfrmigen messenden Zelle, samt der Simulation des Vergleichs der Verbreitung des Mittelwertes der Anzahl von Krnern pro Fl- che zu erlangen. Die erhaltenen Ergebnisse reprsentieren einen Teil der Forschung der Mikrostruktur- Entwicklung beim industriellen Gießen von Blcken der Legierung EN AW-5083 in Abh ngigkeit der lokalen Abkhlgeschwindigkeit der Blcke

A network-specific approach to percolation in networks with bidirectional links

Methods for determining the percolation threshold usually study the behavior of network ensembles and are often restricted to a particular type of probabilistic node/link removal strategy. We propose a network-specific method to determine the connectivity of nodes below the percolation threshold and offer an estimate to the percolation threshold in networks with bidirectional links. Our analysis does not require the assumption that a network belongs to a specific ensemble and can at the same time easily handle arbitrary removal strategies (previously an open problem for undirected networks). In validating our analysis, we find that it predicts the effects of many known complex structures (e.g., degree correlations) and may be used to study both probabilistic and deterministic attacks.Comment: 6 pages, 8 figure