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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Estudo experimental do comportamento à fratura frágil em aços estruturais ferríticos e aplicações à determinação da curva mestra. / Experimental study on the cleavage fracture behavior of structural ferritic steels and applications to determine the master curve.

Rafael Guimarães Savioli 13 April 2016 (has links)
Este trabalho apresenta uma investigação experimental sobre o comportamento à fratura frágil de aços estruturais ferríticos, ASTM A285 Gr C e ASTM A515 Gr 65. Os resultados deste trabalho ampliam a base de dados de propriedades mecânicas utilizadas nas análises de integridade de estruturas pressurizadas tais como vasos de pressão e tanques de armazenamento construídos com esta classe de material. O trabalho tem por objetivo também avaliar a aplicabilidade de corpos de prova de dimensões reduzidas, PCVN, na determinação da temperatura de referência, T0, por meio da metodologia da Curva Mestra, a qual define a dependência da tenacidade à fratura do material em função da temperatura. Os ensaios de tenacidade à fratura foram conduzidos utilizando-se corpos de prova solicitados em flexão três pontos com geometria SE(B), PCVN e PCVN com entalhe lateral, extraídos de chapas laminadas. Os resultados dos ensaios foram obtidos em termos de integral J no momento da instabilidade, denotados por Jc. Dados adicionais de resistência à tração e de Impacto Charpy convencional também foram obtidos para caracterizar o comportamento mecânico dos aços utilizados. Os resultados mostraram uma forte influência da geometria dos corpos de prova sobre os valores de Jc, evidenciada pela grande variação nos valores de tenacidade à fratura. / This work presents an experimental investigation on the cleavage fracture behavior of structural ferritic steels, ASTM A285 Grade C and ASTM A515 Grade 65. One purpose of this study is to enlarge a previously reported work on mechanical and fracture properties for this class of steel to provide a more definite database for use in structural and defect analyses of pressurized components, including pressure vessels and storage tanks. Another purpose is to address the applicability of Precracked V-notch Charpy specimens to determine the reference temperature, T0, derived from the Master Curve Methodology which defines the dependence of fracture toughness with temperature for the tested material. Fracture toughness testing conducted on single edge bend specimens in three-point loading (SE(B), PCVN Plain Side and PCVN Side Grooved) extracted from laminated plates provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc. Additional tensile and conventional Charpy tests produce further experimental data which serve to characterize the mechanical behavior of the tested materials. The results reveal a strong effect of specimen geometry on Jc values associated with large scatter in the measured values of cleavage fracture toughness.
42

ASTM D5231 aplicada à caracterização da composição gravimétrica dos resíduos sólidos urbanos : estudo de caso : Novo Hamburgo, RS

Waskow, Régis Pereira January 2015 (has links)
O presente trabalho avaliou a composição gravimétrica dos resíduos sólidos urbanos (RSU) do município de Novo Hamburgo-RS. Foram realizadas 10 amostragens de diferentes setores de coleta ao longo dos meses de março e abril de 2014. Juntamente com a análise da composição gravimétrica foi avaliada a densidade dos RSU de Novo Hamburgo. No mesmo período foram realizadas amostragens da saída das esteiras de triagem da central de transbordo do município, com um total de 5 amostras. Os procedimentos amostrais seguiram a norma americana ASTM D5231/2008. A composição gravimétrica obtida para os RSU corresponde em: 57,13% matéria orgânica; 14,82% plástico; 12,69% papel; 4,34 têxtil; 1,62% metais ferrosos; 0,69% borracha; 0,49% metais não ferrosos; 0,40% couro; 0,35% madeira e 3,86% outros. O valor médio para a densidade do RSU encontrado foi de 173 kg/m³. Alguns resíduos encontrados como eletroeletrônicos, pilhas e baterias, embalagens contaminadas com óleo, alguns resíduos sólidos industriais (RSI) e outros, não deveriam ser destinados junto aos RSU. A maior fração da matéria orgânica era esperada visto que este comportamento é identificado na composição gravimétrica média dos RSU do Brasil. Os resultados demonstram um potencial para implantação do processo de compostagem pelo alto potencial de resíduos orgânicos, sendo necessário mais análises para garantir a qualidade e aplicabilidade do composto. O descarte inadequado de resíduos orgânicos e recicláveis juntos inviabiliza a reciclagem, aumentando as quantidades destinadas ao aterro sanitário. A composição gravimétrica obtida para a saída das esteiras de triagem corresponde em: 81,60% matéria orgânica; 8,63% plástico; 2,89% papel; 1,66 têxtil; 0,58% borracha; 0,52% metais ferrosos; 0,37% metais não ferrosos; 0,35% madeira; 0,23% couro e 1,81% outros. Foi identificada uma grande presença de materiais recicláveis na saída das esteiras de triagem. Ações foram propostas para aumentar a eficiência do processo de triagem e melhorar o aproveitamento dos recicláveis. Políticas públicas foram sugeridas visando à melhoria dos processos de gestão dos RSU do município. Os resultados obtidos são representativos para o período avaliado, sendo passíveis de alteração quando de amostragem em outros períodos. / The purpose of this paper is evaluate the gravimetric composition of Municipal Solid Waste (MSW) of Novo Hamburgo - RS. Ten samples were collected in different areas between March to April 2014 according to ASTM D5231/2008. Simultaneously were evaluated the MSW density and the materials collection after sorting followed the ASTM D5231/2008. The gravimetric composition of MSW consists in 57,13% of organic matter; 14,82% of plastic; 12,69% of paper; 4,34% of textile; 1,62% of ferrous metals; 0,69% of rubber; 0,49% of noun ferrous metals; 0,40% of leather; 0,35% of wood and 3,86% of others. The MSW density were 173 kg/m³. Some residues as electronics, batteries, oil contaminated packaging and some industrial solid waste should not be disposed as MSW. A larger fraction of organic matter was expected as shown in the most Brazilian analyzed papers since that behavior is known about the gravimetric average composition of MSW in Brazil. The results demonstrate the potential implementation of the composting process considering the amount of organics, requiring further analysis to ensure the quality and applicability of the produced compounds. The inappropriate disposal of organic matter and recyclables together turn unfeasible the recycling. The gravimetric composition of material after sorting consists in: 81,60% of organic matter; 8,63% of plastic; 2,89% of paper; 1,66 of textile; 0,58% of rubber; 0,52% of ferrous metals; 0,37% of non ferrous metals; 0,35% of wood; 0,23% of leather e 1,81% of others. Amounts of recyclables was identified after sorting and based on this evidence actions were proposed to increase the sorting process efficiency and improve the recycling. Public policies were recommended to enhance the MSW management. The results are representative considering this measuring period, which could change if realized in another periods.
43

Caracterização microestrutural e mecânica de juntas soldadas utilizando os processos GTAW, FCAW e SMAW

Lima Júnior, Diniz Ramos de 31 January 2013 (has links)
Submitted by João Arthur Martins (joao.arthur@ufpe.br) on 2015-04-16T18:56:30Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Biblioteca_Diniz Ramos de Lima Junior pdf.pdf: 5006107 bytes, checksum: a48c411c4d1e3bfb09f9032dfde70aa3 (MD5) / Made available in DSpace on 2015-04-16T18:56:30Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Biblioteca_Diniz Ramos de Lima Junior pdf.pdf: 5006107 bytes, checksum: a48c411c4d1e3bfb09f9032dfde70aa3 (MD5) Previous issue date: 2013 / LIMA JÚNIOR, Diniz Ramos de. Caracterização microestrutural e mecânica de juntas soldadas utilizando os processos GTAW, FCAW e SMAW. Recife, 2013. 81 f. Dissertação (mestrado) - UFPE, Centro de Tecnologia e Geociências , Programa de Pós-graduação em Engenharia Mecânica, 2013..
44

AvaliaÃÃo dos Efeitos da TÃcnica da Dupla Camada na Soldagem do AÃo ASTM A 516 Grau 60 / Technical Evaluation of the Effects of the Double Layer in Welding Steel ASTM A 516 Grade 60

Ricardo Liarth da Silva Cruz 13 November 2006 (has links)
O aÃo ASTM A 516 Grau 60 à um aÃo estrutural ligado ao manganÃs, extensamente utilizado na indÃstria petrolÃfera em operaÃÃes de armazenamento, transporte e processamento de produtos petrolÃferos em condiÃÃes que apresentam requisitos de tenacidade. Quando o reparo de estruturas construÃdas com esse aÃo envolve soldagem convencional, ocorre a formaÃÃo de estrutura martensÃtica na zona afetada pelo calor (ZAC) bem como o estabelecimento de tensÃes residuais ao longo da junta. Os procedimentos de reparo para o aÃo ASTM A516 Grau 60 estabelecem o uso de um tratamento tÃrmico para alÃvio de tensÃes logo apÃs a soldagem, tal tratamento vem como uma alternativa capaz de reduzir/minimizar efeitos danosos originados na regiÃo da solda. Todavia, algumas vezes podem ser tecnicamente impraticÃveis ou representar um aumento de custo significativo, de forma que um procedimento de soldagem sem tratamento tÃrmico pÃs soldagem (TTPS), que resulte em baixos nÃveis de tensÃes residuais e adequadas propriedades quÃmicas e mecÃnicas da junta à extremamente importante. Neste contexto, este trabalho foi proposto visando contribuir com os estudos de reparos por soldagem, com qualidade e sem a necessidade de um TTPS, atravÃs da aplicaÃÃo da tÃcnica da dupla camada. Os ensaios deste trabalho foram conduzidos em amostras do aÃo ASTM A 516 Grau 60 com 38 mm de espessura, soldados manualmente com eletrodos bÃsicos, em juntas chanfradas em K e em semi V, que foram avaliados na condiÃÃo como recebido; soldado com o procedimento convencional sem TTPS e com TTPS; e soldado com a tÃcnica da dupla camada. As relaÃÃes de energia para a aplicaÃÃo da dupla camada foram definidas apÃs a aplicaÃÃo do Teste de Higuchi convencional (dureza) e modificado (microestrutura). Para todas as juntas foram avaliados os perfis de microdureza, a microestrutura, a energia absorvida ao impacto e os perfis de tensÃes residuais.Os resultados demonstraram que a aplicaÃÃo da tÃcnica de soldagem com dupla camada, usando combinaÃÃes adequadas de energia de soldagem, definidas pelo Teste de Higuchi, pode-se alcanÃar reduÃÃes dos nÃveis de dureza na ZAC; refinamento microestrutural; propriedades mecÃnicas finais melhoradas, porÃm com sinais evidentes de tensÃes residuais elevadas no Metal de Solda e no Metal Base. / Steel ASTM A 516 Grade 60 is connected to a manganese structural steel, widely used in oil industry operations in storage, transport and processing of petroleum products in conditions that present requirements of toughness. When the repair of structures constructed with the conventional steel involves welding, there is the formation of martensitic structure in the heat affected zone (HAZ) and the establishment of residual stresses along the joint. The repair procedures for ASTM A516 Grade 60 establish the use of a heat treatment for stress relieving after welding, such as an alternative treatment is able to reduce / minimize the harmful effects arising in the region of the weld. However, they can sometimes be technically impractical or represent a significant cost increase, so that a welding procedure without post weld heat treatment (TTPs), which results in low levels of residual stresses and adequate chemical and mechanical properties of the joint is extremely important. In this context, this work has been proposed to contribute to studies of repair by welding, quality and without the need for TTPs, by applying the technique of the double layer. The essays in this work were conducted on samples of steel ASTM A 516 Grade 60 to 38 mm thick, welded manually with basic electrodes, beveled joints in K and semi V, which were evaluated in the condition as received; soldier with the conventional procedure without TTPs and TTPs, and soldiers with the technique of the double layer. The energy relations for the application of the double layer were defined after the application of conventional test Higuchi (hardness) and modified (microstructure). For all joints were evaluated the profiles of microhardness, microstructure, the energy absorbed the impact and stress profiles residuais.Os results demonstrated that the application of welding technique with double-layer, using appropriate combinations of welding power, defined Test Higuchi, can achieve reductions in levels of hardness in HAZ; microstructural refinement, improved final mechanical properties, but with signs of high residual stresses in the weld metal and base metal.
45

Estudo da Temperatura de SolubilizaÃÃo de AÃos InoxidÃveis AustenÃticos ASTM A312 TP321 para OperaÃÃo em IndÃstria PetroquÃmica / Study of Temperature Solubilization of Austenitic Stainless Steels ASTM A312 TP321 for Operation in Petrochemical Industry

Marcelo Josà Gomes da Silva 23 March 2001 (has links)
FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / AÃos inoxidÃveis austenÃticos sÃo bem conhecidos por sua resistÃncia à corrosÃo e por apresentarem boas propriedades mecÃnicas a temperaturas altas. Estes aÃos estÃo sujeitos à corrosÃo intergranular causada pela segregaÃÃo de carbono no contorno de grÃo formando carbonetos M23C6 ricos em cromo. A regiÃo prÃxima ao contorno de grÃo se torna mais pobre em cromo e susceptÃvel à corrosÃo. Diz-se que esta regiÃo està sensitizada. Para evitar este problema, elementos estabilizantes como Ti (AISI 321) e Nb (AISI 347) sÃo adicionados para causar a formaÃÃo de TiC ou NbC, que reduzem o conteÃdo de carbono em soluÃÃo sÃlida. Mesmo com a utilizaÃÃo de aÃos estabilizados, para certas condiÃÃes de temperatura, ocorre a segregaÃÃo dos carbonetos ricos em cromo para a regiÃo dos contornos de grÃo, tornando necessÃrio tratar termicamente o aÃo anteriormente à sua utilizaÃÃo. Neste trabalho foi estudado o comportamento do aÃo ASTM A312 TP321 a partir do estado como recebido e submetido Ãs temperaturas de 380ÂC e 600ÂC por diferentes perÃodos. Foi tambÃm estudada uma temperatura de solubilizaÃÃo que minimizasse a sensitizaÃÃo deste material para posterior operaÃÃo Ã600ÂC, tanto para o material no estado como recebido, como para material apÃs um ano de operaÃÃo na indÃstria petroquÃmica. Foram realizados tratamentos tÃrmicos de solubilizaÃÃo à 900, 950, 1000 e 1050ÂC em seguida as amostras foram submetidas Ã600ÂC por 15 minutos, 3, 10, 50 e 100 horas. ApÃs cada tratamento foi realizada uma caracterizaÃÃo microestrutural por tÃcnicas de microscopia eletrÃnica de varredura e microscopia Ãtica. Foram entÃo realizados ensaios de reativaÃÃo potenciocinÃtica para avaliar o grau de sensitizaÃÃo das amostras. A exposiÃÃo de amostras de aÃo ASTM A312 TP321 à temperatura de 600ÂC acarretou na sensitizaÃÃo das mesmas, porÃm sua exposiÃÃo à 380ÂC nÃo veio a causar este mesmo efeito. O tratamento tÃrmico de solubilizaÃÃo à 900ÂC anteriormente a exposiÃÃo à 600ÂC teve efeito no sentido de reduzir a sensitizaÃÃo deste material, mostrando ser o mais indicado para estas condiÃÃes de utilizaÃÃo. / Austenitic stainless steels are well known for its corrosion resistance and good mechanical properties present at high temperatures. These steels are subject to intergranular corrosion caused by carbon segregation at grain boundary forming M23C6 carbides rich in chromium. The region near the grain boundary becomes poorer in chromium and susceptible to corrosion. It is said that this region is sensitized. To avoid this problem, stabilizing elements such as Ti (AISI 321) and Nb (AISI 347) are added to cause the formation of TiC and NbC, which reduce the content of carbon in solid solution. Even with the use of steel stabilized to certain conditions of temperature, there is segregation of chromium rich carbides in the region of the grain boundaries, making it necessary heat treating the steel prior to use. This paper studied the behavior of ASTM A312 TP321 from the state as received and subjected to temperatures of 380  C and 600  C for different periods. We also studied a solubility temperature that minimizes the sensitization of this material for subsequent operation A600  C, both for the material in the as-received, as to the material after one year of operation in the petrochemical industry. Thermal treatments were performed to solubilization 900, 950, 1000 and 1050  C and then the samples were subjected A600  C for 15 minutes, 3, 10, 50 and 100 hours. After each treatment was performed by a microstructural characterization techniques, scanning electron microscopy and optical microscopy. Tests were then performed reactivation potenciocinÃtica to assess the degree of sensitization of the samples. The exposure of samples of ASTM A312 TP321 at a temperature of 600  C resulted in sensitization of the same, but their exposure to 380  C did not come to cause this same effect. The heat treatment of solubilization at 900  C prior to exposure to 600  C resulted in reducing the sensitization of the material, showing to be more appropriate to these conditions.
46

Comparison of methods for measurement of dust deposition in South African mining sectors

Kwata, Maphuti Georgina January 2014 (has links)
Dust particles in the atmosphere are a key cause of nuisance, health and other environmental problems. The mining sector is a major source of airborne particulate matter caused by operations like terrain clearing, drilling, blasting, tipping and loading and the passage of vehicles on unpaved roads. The nuisance effect of airborne dust can be measured by using dust buckets and/or directional dust deposition gauges. Dust buckets are used to determine vertical dust deposition rates and directional dust deposition gauges are used to determine the direction of the sources. Traditionally the measurement of the vertical flux of dust, or dust deposition has been used as to indicate the nuisance caused by coarse suspended particulate matter. Several countries have produced standards for permissible dust deposition rates. Although alternative deposition measurement methods have been proposed, ASTM D1739 has remained the method most often used in the South African mining and industrial sectors to measure dust deposition. In addition, a number of non-standard directional dust deposition gauges have been used. SANS 1929:2005 (South African National Standards, 2005) prescribes the use of ASTM D1739:98 for measuring dust deposition. However, for historical reasons the previous version, ASTM D1739:70 (re-approved as ASTM D1739:82) is still widely used and in the recently promulgated South African Dust Management regulations the use of this version is prescribed. In order to determine the difference in the results obtained by the two versions, ASTM D1739:82 and ASTM D1739:98 were used to measure dust deposition levels arising from a coal mining operation in the Mpumalanga Province and a gold mining operation in North-West Province. In order to determine whether a correlation exists between vertical dust flux (dust deposition) and horizontal dust flux, standard directional horizontal dust flux gauges according to BS 1747 part 5 were also set up at both sites. The measurement of dust deposition using three dust deposition gauges (i.e. ASTM D1739:82, ASTM D1739:98 and BS 1747 part 5, directional dust deposition gauges) was undertaken monthly over a period of fourteen (14) months at the two sites. The findings of the study indicate that the dust deposition rates for an opencast coal mine are generally higher than the dust deposition rates for an underground gold mine. ASTM D1739:98 was shown to be a more efficient dust deposition collection method than ASTM D1739:82, with the ratio between the mean values slightly more than 2. The addition of water to the dust bucket does not make a statistically significant difference to retention of dust in the bucket. There is a weak correlation between results for the vertical dust gauges and horizontal dust flux. It is recommended that the South African mining sector continue dust deposition monitoring and reporting using the more recent version of ASTM D1739, as high deposition levels may indicate a potential health impact from PM10 thoracic dust. / Dissertation (MEng)--University of Pretoria, 2014. / gm2014 / Chemical Engineering / unrestricted
47

[en] CHARACTERIZATION OF THE OXIDIZED LAYER OF ALLOY ASTM F15 OBTAINED UNDER DIFFERENT SURFACE CONDITIONS / [pt] CARACTERIZAÇÃO DA CAMADA OXIDADA OBTIDA EM DIFERENTES CONDIÇÕES DE SUPERFÍCIE DA LIGA ASTM F15

MARCELO BELMIRO GOMES DE SOUTO 25 January 2016 (has links)
[pt] A liga ASTM F15 é usada para o encapsulamento de componentes ou dispositivos eletrônicos em virtude de seu baixo coeficiente de expansão térmica que é similar à de vidros duros. Na construção de juntas vitro metálicas com características de hermeticidade a formação de uma camada de óxido na superfície metálica é necessária para que ocorra o molhamento adequado desta superfície pelo sealing glass. Neste trabalho foram utilizados dois tipos de superfícies, subdivididos em grupos, de modo a avaliar a sua influência na formação da camada oxidada. As superfícies foram oxidadas à temperatura de 800 graus C, em atmosfera ambiente, variando o tempo de oxidação em 5, 10, 20 e 40 minutos, seguido de resfriamento ao ar. As camadas de óxido foram caracterizadas quanto a sua morfologia e composição química, utilizando Microscopia Eletrônica de Varredura (MEV), Microscopia Ótica (MO), Difração de Raio X (DRX) e Espectroscopia de emissão e fótons de raio X (XPS) e Rugosimetria. As camadas de óxido foram avaliadas em função do ganho de massa superficial, espessura, composição química e rugosidade da superfície metálica. Os principais produtos de oxidação, nas condições estudadas foram Hematita (Fe2O3), Magnetita (Fe3O4) e Taenita (FeNi). Foi observado que e as condições superficiais de rugosidade não influenciaram o tipo de produtos de oxidação obtido, porém se obteve maiores ganhos de massa para as superfícies polidas mecanicamente. / [en] The alloy ASTM F15 is used for the encapsulation of components or electronic devices because of its low coefficient of thermal expansion that is similar to hard glasses. In construction joints glass-to-metal tightness with characteristics forming an oxide layer on the metallic surface is required so that adequate wetting takes place at the surface of this sealing glass. This study looked at two types of surfaces, subdivided into groups in order to assess their influence on the oxide layer. One group was subjected to mechanical polishing and the other group subjected to chemical polishing. The surfaces were oxidized at a temperature of 800 degrees C in the ambient atmosphere by varying the oxidation time at 5, 10, 20 and 40 minutes, followed by cooling to air. As oxide layers were characterized for their morphology and chemical composition, using Scanning Electron Microscopy (SEM), Optic Microscopy, X-Ray Diffraction (XRD) and Emission spectroscopy and X-ray photons (XPS) and Rugosimeter.The oxide layer was evaluated in terms of surface mass, thickness, chemical composition and surface roughness of the metal surface. The main oxidation products under the conditions studied were Hematite (Fe2O3), Magnetite (Fe3O4) and Taenita (FeNi). It was observed that, surface roughness conditions did not influence the type of oxidation products obtained, but it had greater mass gains for the mechanically polished surfaces.
48

A Relationship Between the Strengths of Type N Cubic Mortar Specimens and In-Situ Mortar

Reynolds, Michael Scott 01 May 2019 (has links)
The compressive strength of mortar is typically determined using the American Societyfor Testing and Materials (ASTM) standard method using 2 inch cubes which are compressed tillfailure. There is however a disparity between the compressive strengths of mortar cubes, and insitumortar. This disparity is a result of the differences in thickness, aspect ratio, curingconditions, water content, and confinement between mortar cubes and mortar joints. While thesedifferences lead to mortar joints being stronger than mortar cubes, a relationship between theirstrengths is desired.Two less-common mortar strength tests were used to determine more accurately thecompressive strength of in-situ mortar. The results of both tests were compared to the results ofASTM standard compressive testing with mortars of the same water content. The first was theDouble Punch test which involves the use of two metal punches that compress either side of athin mortar sample till failure. The Double Punch test is more difficult to perform than theASTM standard compression test, but was useful because it simulates the confinement that insitumortar will experience. The Double Punch test was also used with mortar specimens ofvarying thickness to determine a relationship between specimen thickness and compressivestrength. The second test used was the Helix Pullout test. This test is performed by insertingmetal helical screws into a mortar joint, and pulling from the joint while restricting rotation. Themaximum load used to extract the Helix is recorded as the Pullout Load, and is used to find thecompressive strength by use of a calibration curve. This test was used on a masonry wall paneland mortar cubes were also made with the same mortar for compressive testing.The tested mortar exhibited decreased compressive strength with increased water content.The mortar also decreased in strength with increasing specimen thickness. Mortar joints wereshown to be significantly stronger than mortar cubes based on factors of specimen thickness andconfinement by an average factor of at least 2.40. Although results are affected by punchdiameter, the Double Punch test was shown to be a consistent and reliable means of estimatingmortar compressive strength. The Helix Pullout test exhibited wide variation, and wasdetermined to be primarily useful for qualitative comparison as opposed to quantitativedetermination of strength.
49

Zkoušky kavitační eroze kavitujícím paprskem / Cavitation testing using cavitating jet

Rovder, Juraj January 2021 (has links)
This thesis deals with the issue of cavitation and its effects. In this context, it describes the mechanism of origin and implosion of cavities and cavitation regimes. It lists various types of hydrodynamic cavitation. It presents the Rayleight-Plesset equation and describes micro jet. It also highlights cavitation erosion and the effects of cavitation on some types of materials. It deals with three types of cavitation resistance testing, namely cavitation tunnels, a vibrating cavitation system, supported by the ASTM G32 standard, and last but not least, cavitation nozzles, which follow the ASTM G134-17 standard. In correlation with cavitation nozzles, it frames its four basic parameters, which are stand of distance, the cavitation number, the speed of sound and the geometry of the nozzle. At the end of the theoretical part it characterizes the construction of test bench. The practical part is focused on performing the experiment. It first presents the procedure for carrying out the experiment and then evaluates this experiment. Part of the evaluation is the visual observation of selected samples of AlCu4Mg1Mn1 material and the monitoring of cavitation erosion on specific samples. First, these data are processed in the form of graphs and tables. It uses a microscope as a tool for detailed observation of samples. The conclusion of the practical part is devoted to the evaluation of the experiment.
50

Exploring the Molecular Origin of Jet Fuel Thermal Oxidative Deposition Through Statistical Analysis of Mass Spectral Data and Pyrolysis Gas Chromatography/Mass Spectrometry of Deposits

Christison, Krege Matthew 01 January 2019 (has links)
ASTM D3241 (Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels) measures the thermal oxidative stability of jet fuels under elevated temperature and pressure conditions. When jet fuels fail ASTM D3241, either at the refinery or in the distribution system, there can be supply disruptions and financial losses. Understanding the causes of poor thermal oxidative stability in jet fuels could help prevent or mitigate issues. In order to develop a deeper understanding of the molecular precursors that lead to ASTM D3241 failures, a number of analytical methodologies and data treatment techniques have been developed, applied, and reported here. Statistical analysis of LC/MS ESI data from jet fuels with varying thermal oxidative stabilities allows for the identification of molecules that are significant to ASTM D3241 failures. Differential statistical analysis of LC/MS ESI data from jet fuels before and after thermal oxidative stressing in a QCM reactor elucidates which significant molecules are being consumed during oxidation and which molecules are increasing in abundance. The analysis of thermal oxidative deposits that form during thermal oxidative stressing in the QCM reactor allows for the insight into the molecular components of the deposits. Attapulgus clay removes the polar molecules that lead to thermal oxidative stability issues in the refinery. Extraction of Attapulgus clay that has been used in a refinery to filter jet fuel with a series of solvents removes the polar molecules into a series of fractions. The subsequent analysis of the fractions by comprehensive GCxGC/MS leads to the identification of the different homologous series of molecules that are removed by the clay. The analyses developed and employed here are shown to be particularly useful for the analysis of trace polar nitrogen and oxygen containing molecules. Similar homologous series of molecules are identified across all of the different analyses. It is also clear from some of the analyses, along with previously reported data in the literature, that reactive sulfur-containing molecules are significant to poor thermal oxidative stability as measured by ASTM D3241 and to the formation of thermal oxidative deposits. There is still an opportunity to find methodologies to better characterize the sulfur species present and correlate them to the data that is reported here.

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