The aim of the diploma thesis is to study fatigue properties of EN AW-2618A aluminium alloy produced by selective laser melting (SLM). S-N diagrams of reference alloy and SLM material depending on manufacturing conditions were constructed. Reference alloy had the same chemical composition as the SLM material, but it was made by traditional technology (by extruding). While testing, acoustic emission (AE) and resonant frequency of loading was monitored. Fractographic analyses of fracture surfaces were performed. It was found, that SLM material has significantly worse fatigue performance. Fatigue properties are strongly dependent on SLM process parameters settings and precise observance of procedure. The most significant differences in cyclic degradation were found in the length of the stages of fatigue. The more homogeneous the material is, the longer the nucleation stage compared to the total lifetime is. The main source of AE in case of the reference material is plastic deformation on the tip of the crack. For SLM testing, stronger acoustic activity was recorded, because brittle fracture of the material between discontinuities, which is stronger AE source, is more frequent.

This diploma thesis deals with finding copper alloy suitable for processing SLM technology and determining the process parameters leading to a relative density close to the full material. The theoretical part provides an insight into additive technology and the processing of new alloys in SLM. Work also contains a search report of processed copper alloys used in SLM. Based on the theoretical part were designed test samples and method of evaluation. Samples were produced by melting metallurgical powder using ytterbium laser with an output power 400 W. The testing is divided into three stages; Determination of the parameters of the SLM process, Debug strategies for larger parts, Geometric precision and mechanical testing. Based on the results was determined dependence of relative density on the input parameters. For the best parameters were determined geometric precision correction and mechanical properties.

<div> <p>The electric arc furnace (EAF) is one of the most widely-used steelmaking process recycling the scrap as the raw material. Electric arc furnace steelmaking is a material-dependent and energy-consuming process. The electricity is utilized as the main heat source to melt the scrap by the electric arc discharging from the graphite electrodes. Since the plasma arc weld has the very similar heat transfer mechanism and melting phenomenon comparing with the scrap melting in EAF process, the model development for the free-burning arc, the arc-metal heat transfer, and the metal melting will refer to the research of plasma arc weld field and start with a relatively small scale. In this study, a comprehensive computational dynamics (CFD) model was developed to predict the heat transfer from the electric arc to the metal anode, which is composed of the DC electric arc model, solidification and melting model, and the arc-metal heat transfer model. The validation of the CFD models has been conducted utilizing the experimental data and simulation results in other literature. The commercial software, ANSYS FLUENT^®, was employed with the User-Defined Function scripts and the User-Defined Scalar to model the magnetic field, comprehensive flow field, and high temperature field. Furthermore, the parametric studies for the process of the anode melted by the plasma arc were performed to investigate the effects of the arc current and the initial anode temperature on the anode melting. The results reveal that the value of the arc current has a positive correlation with the arc temperature and velocity but has negative correlation with the penetration time of the anode. Meanwhile, with the increase of anode initial temperature, the metal penetrate time will decrease.</p> </div> <br>

This thesis summarizes our latest findings on liquid-solid equilibria for fluids in confined spaces. In the first part of the thesis we introduce a microscopic lattice model which we have developed for the exploration of the freezing and melting phenomena in mesoporous solids with arbitrary geometries of the pore spaces. By applying this model to materials with well-ordered pore structures we (i) establish the mechanisms of the freezing and melting transitions and identify the equilibrium and metastable transition branches for different boundary conditions, (ii) illuminate the role of thermodynamic fluctuations, and (iii) find rigorous equations governing the transition temperatures for the lattice model considered. In the second part of the thesis the results obtained with the ordered pore systems are used for an in-depth analysis of the transitions occurring in geometrically disordered porous solids. First, by considering the ink-bottle pore geometry the efficacies of the different phase transition mechanisms established in the first part are elucidated. As a particularly important result, it is shown that thermodynamic fluctuations may alter the transition mechanisms. In the light of these findings the freezing and melting behaviors in statistically disordered porous materials are discussed. In the third part of the thesis several experimentally-relevant topics are considered and the potentials of the microscopic model for evaluation of the experimental data are demonstrated.

miRNAs are short non-coding RNA molecules which play role in post-transcriptional regulation of gene expression. Thus, miRNAs are related to a variety of physiological processes and diseases, e.g. some tumours or viral infections. In this diploma thesis we studied temperature-induced dissociation of complexes that simulated pairing of miRNA with target mRNA. For these purposes we used UV absorption spectroscopy and Raman spectroscopy. Measured spectra were then treated by means of a factor analysis. The aim of the thesis was to determine thermodynamic parameters of the complexes dissociation and to clarify how inner loops and bulges affect the stability of oligonucleotide duplexes. Also, we have tested the suitability of the used approach for study of oligonucleotide complexes. We have shown that factor analysis of temperature dependent UV absorption spectra is a proper base to determine thermodynamic parameters of the duplex dissociation. Raman spectra were affected by large errors, nevertheless they enabled to observe some structural changes related to the transition. It has been shown that the bulge loop present in the studied complex reduces both its flexibility and the energetic preference of its formation.

[pt] A presente dissertação tem como principal objetivo analisar os efeitos do processo de integração da fusão entre as empresas Y e Z, ambas atuantes no setor de telecomunicações brasileiro, sob a ótica da cultura organizacional. O instrumento de coleta de dados utilizado na pesquisa consistiu de um questionário baseado no modelo conceitual de pesquisa desenvolvido por Liao e Yen (2003), composto de 42 questões, sendo 17 questões relativas à cultura organizacional e 18 questões relativas às atitudes de trabalho dos funcionários, perfazendo um total de 35 questões. As demais questões são relativas às características dos respondentes. O índice de resposta da pesquisa foi de 67 por cento sendo composto por 16 respondentes originários da empresa Y e 14 respondentes originários da empresa Z. A análise dos dados com intuito de mapear diferenças entre as percepções dos funcionários originários das empresas Y e Z foi efetuada por intermédio do teste estatístico não paramétrico de Mann-Whitney (teste-U) em virtude da violação dos requisitos de normalidade para aplicação do teste t-Student. Os resultados estatísticos da pesquisa apontam para a existência atual de percepções culturais distintas entre os membros originários de cada empresa, sugerindo, portanto, que o processo de integração da fusão ainda está incompleto. / [en] This dissertation has the purpose of examine the effects of the integration process between the merger of companies Y and Z, both active in the Brazilian telecommunications industry, from the perspective of organizational culture. The data collection instrument used in the study consisted of a questionnaire based on the conceptual research model developed by Liao and Yen (2003), composed of 42 questions, 17 questions relating to organizational culture and 18 questions relating to employee work attitudes, for a total of 35 questions. The remaining issues are related to the characteristics of respondents. The survey response rate was 67per cent and is composed of 16 respondents originating from company Y and 14 respondents originating from company Z. Data analysis with the aim of mapping differences between the perceptions of employees from the companies Y and Z was made through a non-parametric statistical test, Mann-Whitney (U-test), due to the violation of the requirements for normal application of the t-test. The statistical results of the research point to the existence of different cultural perceptions among the members from each previous company, thereby implying that the merger integration process is still incomplete.

The waste treatment, particularly the thermal treatment of waste has changed fundamentally in the last 20 years, i.e. from facilities solely dedicated to the thermal treatment of waste to facilities, which in addition to that ensure the safe plant operation and fulfill very ambitious criteria regarding emission reduction, resource recovery and energy efficiency as well. Therefore this contributes to the economic use of raw materials and due to the energy recovered from waste also to the energy provision. The development described had the consequence that waste and solid recovered fuels (SRF) has to be evaluated based on fuel criteria as well. Fossil fuels – coal, crude oil, natural gas etc. have been extensively investigated due to their application in plants for energy conversion and also due to their use in the primary industry. Thereby depending on the respective processes, criteria on fuel technical properties can be derived. The methods for engineering analysis of regular fuels (fossil fuels) can be transferred only partially to SRF. For this reason methods are being developed or adapted to current analytical methods for the characterization of SRF. In this paper the possibilities of the energetic utilization of SRF and the characterization of SRF before and during the energetic utilization will be discussed.

3D printing, also known as additive manufacturing (AM), has got rapidly developed since 1987. Compared with conventional manufacturing methods, 3D printing provides some advantages such as increasing material utilization and less waste of material. Maraging steel provides good strength and toughness without losing ductility, which has been used for the 3D printing technique. Selective laser melting (SLM) is one of the 3D printing methods, which is mostly used for metal and alloy powder. In this thesis, selective laser melting will be used for maraging steel. 3D printing maraging steel is a new material, the research about the properties of 3D printing maraging steel is still ongoing. Corrosion resistance is one of the most important properties of maraging steel due to the high cost of corrosion. So this thesis will focus on the corrosion behavior of 3D printing maraging steel. The purpose of this thesis was to find the best heat treatment condition for high corrosion resistance and to find the relationship between microstructure and corrosion behavior of maraging steel. In this thesis, several kinds of maraging steel samples with different heat treatment conditions were used. SLM, SLM austenized&amp;quenched, SLM aged, conventional austenized&amp;quenched, and conventional aged. Besides, two kinds of solutions were produced, NaOH (pH=11.5) and Na2SO4 (pH=6.5). To observe the microstructure, an optical microscope was used. The grain size is different between SLM and conventional samples, and also different between the samples with different heat treatment conditions. The potentiodynamic polarization method was used to measuring the corrosion behavior. SLM samples have much lower current density, and the passivation potential and the corrosion rate are similar compared with conventional samples. But due to the lack of further experiments, the relationship between corrosion behavior could be affected by the combined effect of several factors.

Selective laser melting has shown incredible growth as a metallic additive manufacturing process in recent years. While it does provide many solutions and new ways to approach challenges, it does not come without issues of its own, namely, surface roughness. In the as-printed state, the surface roughness of selectively laser melted parts is unacceptable for use in engineering applications. Additionally, selective laser melting is used to produce complex geometries with hard to reach features, preventing conventional mechanical polishing from being successful. Therefore, it is necessary to evaluate non-mechanical polishing processes as treatments for surface roughness. In this study, electrochemical and laser polishing were investigated as potential start-to-finish treatments for the surface roughness of selectively laser melted parts. Following this preliminary study, a follow-up study investigating the effect on the mechanical strength of a lattice design that electropolishing would have. Electropolishing was found to significantly reduce the surface roughness of the as-printed part, but not to a usable value. Additionally, electropolishing was found to be unacceptable for use on lattice parts. Laser polishing was found to significantly reduce the surface roughness of the part but had feature size issues preventing a perfectly smooth surface.

A drill tool body operates under tough cutting conditions where it is subjected to severe rubbing at the drill flute margin by the sliding chips. The tool wear caused by the contact stresses of the high-speed sliding chips is one of the common damage mechanisms observed in drill tool bodies. The present investigation is aimed at evaluating the wear properties, mechanical properties and tribological characteristics of the selective laser melting (SLM) produced drill bodies of Co-alloyed tool steels. Two different maraging steel powders, Modified 18Ni300 and Osprey MAR were the materials of interest in this work. A ranking was obtained after a detailed examination to select the most suitable cutting tool body material for drilling application. The microstructures of SLM-produced materials after aging were carefully characterized and analyzed. The result shows that both the materials are composed of fine dendritic cellular structures and even exhibit melt pool boundaries. The microhardness values taken on the as-polished samples indicate that Modified 18Ni300 is marginally harder than Osprey MAR. The material pick-up tendency, friction characteristics and wear properties of the two material samples at room temperature were also evaluated using a scratch tester and a pin-on-disc tribometer. The wear volume for the scratch test and the pin-on-disc test was quantified by a 3D optical profilometer. The overall coefficient of friction (COF) and the wear volume was considerably higher for Osprey MAR than Modified 18Ni300 in scratch testing. The increase in COF for Osprey MAR can be attributed to the build-up edge adhered to the moving stylus. Wear characterization of the scratched surface shows secondary plowing which validates the adhesion tendency of Osprey MAR. The results from the pin-on-disc test conform to the scratch results displaying marginally lower COF and wear volume for the Modified 18Ni300 disc specimen. The higher volume loss of pin manufactured from workpiece material SS2541 used against Modified 18Ni300 disc substantiates the better wear characteristics of this material. Characterization of wear on the surface and cross-section of disc samples suggests that the total wear is the result of adhesion by delamination and build-up edge, abrasion, and cellular fracture at the interacting interface. Machining application tests were also conducted to study the chip wear characteristics and facilitate the ranking of the materials concerning wear resistance. Chip breaker wear test was performed with chip breakers of two different surface topography, milled and ground, to evaluate the effect of surface texture and roughness on the wear behavior. The result shows adhesion on the chip breaker surface for both the materials of interest. The wear is higher in Osprey MAR than Modified 18Ni300 in both milled and ground conditions. A series of actual drill tests from SLM-produced drill bodies indicates wear at the drill flute margin. The drill body material at the chip flute margin is abraded by the sliding chips for Osprey MAR exhibiting greater wear than Modified 18Ni300 in which case the flute margin is intact. Adhesion is also seen at the flute surface for both materials. EDS analysis undertaken at the site of wear confirms the adhered material is of the workpiece SS2541. The results from all the aforementioned tests suggest that Modified 18Ni300 has better wear resistance than Osprey MAR. It also indicates that the cellular microstructure of SLM-produced maraging steels is not suitable for sliding wear resistance.