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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

Fretting behavior of AISI 301 stainless steel sheet in full hard condition

Hirsch, Michael Robert. January 2008 (has links)
Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Dr. Richard W. Neu; Committee Member: Dr. David L. McDowell; Committee Member: Dr. Itzhak Green.
42

Avaliação da resistência à fadiga de contato de ferro fundido nodular nitretado por plasma

Wollmann, Daniela 28 September 2012 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação Araucária / Este trabalho apresenta um estudo sobre a resistência à fadiga de contato de um ferro fundido nodular nitretado por plasma. Os experimentos foram realizados em um equipamento do tipo esfera sobre plano. Os corpos de prova foram usinados a partir de uma barra de ferro fundido nodular perlítico e em seguida temperados e revenidos. Após a preparação superficial por meio de retificação, lixamento e polimento, as amostras foram divididas em três grupos: 1) temperadas e revenidas; 2) temperadas, revenidos e nitretadas por plasma por 8 horas a 400 °C; e 3) mesmos parâmetros do grupo 2, porém submetidas a um tratamento adicional de Difusão em forno por 16 horas a 400 °C, visando aumentar a profundidade de camada endurecida e dissolver possíveis traços da formação de camada de compostos. Foram feitas medidas de dureza superficial, perfis de dureza, análises das fases e de tensões residuais por meio de difração de raios-X, rugosidade e microscopia eletrônica de varredura, para a caracterização das amostras em diferentes estágios do trabalho. Os ensaios de fadiga de contato foram realizados com lubrificação e a uma pressão de contato máxima de 3,6 GPa. Análises de Weibull mostraram uma vida em fadiga aproximadamente cinco vezes menor para os corpos de prova nitretados por plasma, com ou sem difusão, apesar destes apresentarem tensão residual compressiva significativamente superior aos temperados e revenidos. A menor vida em fadiga dos corpos de prova nitretados foi atribuída a menor dureza de substrato e a ocorrência de um mecanismo de falha distinto dos mecanismos clássicos de fadiga de contato de rolamento, demonstrado nas análises das superfícies ensaiadas. / This work presents a study on the contact fatigue resistance of a plasma nitrided ductile cast iron. The experiments were carried out using a ball-on-washer machine. Specimens were machined from a perlitic ductile cast iron bar, and then quenched and tempered. After surface grinding and polishing, the specimens were divided into three groups a) the first group was tested after the described process, which means as quenched and tempered; b) the second group was plasma nitridedat 400 °C for 8 hours; c) the third one was plasma nitrided as previously described and submitted to a diffusion process at 400 °C for 16 hours in order to extend the hardened zone and to dissolve any trace of compound layer within the microstructure. Surface hardness, hardness profiles, phase analyses and residual stress measurements by X-ray diffraction, surface roughness and optical and scanning electron microscopy were applied to characterize the surfaces during different stages of this work. Rolling contact fatigue tests were conducted at a maximum contact pressure of 3.6 GPa under flood lubrication. Weibull analysis showed that fatigue lives of plasma nitrided specimens were approximately five times shorter than those just quenched and tempered, even though the residual stress measurements showed significantly higher compressive stresses for the nitride conditions. The lower fatigue life for the plasma nitrided specimens was attributed to the lower matrix hardness and to a failure mechanism distinct from the classical rolling contact fatigue mechanisms, showed by surface analisis.
43

Avaliação da resistência à fadiga de contato de ferro fundido nodular nitretado por plasma

Wollmann, Daniela 28 September 2012 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação Araucária / Este trabalho apresenta um estudo sobre a resistência à fadiga de contato de um ferro fundido nodular nitretado por plasma. Os experimentos foram realizados em um equipamento do tipo esfera sobre plano. Os corpos de prova foram usinados a partir de uma barra de ferro fundido nodular perlítico e em seguida temperados e revenidos. Após a preparação superficial por meio de retificação, lixamento e polimento, as amostras foram divididas em três grupos: 1) temperadas e revenidas; 2) temperadas, revenidos e nitretadas por plasma por 8 horas a 400 °C; e 3) mesmos parâmetros do grupo 2, porém submetidas a um tratamento adicional de Difusão em forno por 16 horas a 400 °C, visando aumentar a profundidade de camada endurecida e dissolver possíveis traços da formação de camada de compostos. Foram feitas medidas de dureza superficial, perfis de dureza, análises das fases e de tensões residuais por meio de difração de raios-X, rugosidade e microscopia eletrônica de varredura, para a caracterização das amostras em diferentes estágios do trabalho. Os ensaios de fadiga de contato foram realizados com lubrificação e a uma pressão de contato máxima de 3,6 GPa. Análises de Weibull mostraram uma vida em fadiga aproximadamente cinco vezes menor para os corpos de prova nitretados por plasma, com ou sem difusão, apesar destes apresentarem tensão residual compressiva significativamente superior aos temperados e revenidos. A menor vida em fadiga dos corpos de prova nitretados foi atribuída a menor dureza de substrato e a ocorrência de um mecanismo de falha distinto dos mecanismos clássicos de fadiga de contato de rolamento, demonstrado nas análises das superfícies ensaiadas. / This work presents a study on the contact fatigue resistance of a plasma nitrided ductile cast iron. The experiments were carried out using a ball-on-washer machine. Specimens were machined from a perlitic ductile cast iron bar, and then quenched and tempered. After surface grinding and polishing, the specimens were divided into three groups a) the first group was tested after the described process, which means as quenched and tempered; b) the second group was plasma nitridedat 400 °C for 8 hours; c) the third one was plasma nitrided as previously described and submitted to a diffusion process at 400 °C for 16 hours in order to extend the hardened zone and to dissolve any trace of compound layer within the microstructure. Surface hardness, hardness profiles, phase analyses and residual stress measurements by X-ray diffraction, surface roughness and optical and scanning electron microscopy were applied to characterize the surfaces during different stages of this work. Rolling contact fatigue tests were conducted at a maximum contact pressure of 3.6 GPa under flood lubrication. Weibull analysis showed that fatigue lives of plasma nitrided specimens were approximately five times shorter than those just quenched and tempered, even though the residual stress measurements showed significantly higher compressive stresses for the nitride conditions. The lower fatigue life for the plasma nitrided specimens was attributed to the lower matrix hardness and to a failure mechanism distinct from the classical rolling contact fatigue mechanisms, showed by surface analisis.
44

Estudo da análise de fadiga pelo MEF considerando os efeitos da estampagem / Study of fatigue analysis by FEM considering the metal stamping effects

Aguado, Clodoaldo Garcia 18 August 2018 (has links)
Orientador: Alfredo Rocha de Faria / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-18T21:18:25Z (GMT). No. of bitstreams: 1 Aguado_ClodoaldoGarcia_M.pdf: 53529976 bytes, checksum: c01081cee3de72ee7fd5c2ac1f9d0612 (MD5) Previous issue date: 2011 / Resumo: As simulações dentro do ambiente de projeto devem prever a utilização de novas variáveis, especialmente de processos, de forma a aumentar a proximidade entre os modelos virtual e real e, com isso, aumentar a precisão das simulações. O objetivo deste trabalho foi o de estudar um modelo pelo Método dos Elementos Finitos que incluísse os efeitos da variação de espessura provenientes do processo de estampagem para a análise de vida em fadiga de um componente do sistema de exaustão automotivo. Primeiramente foi realizada a simulação do processo de estampagem, onde foi possível identificar as mudanças de espessura na geometria do componente estudado. O resultado dessa simulação foi transportado para a malha de elementos finitos, de forma que as análises posteriores, estrutural e de fadiga, considerassem os efeitos da redução e aumento da espessura local. Como base de comparação, as mesmas análises foram realizadas para a condição de espessura constante, tradicionalmente adotada durante a fase de projeto. Utilizando o modelo de Wöhler-Goodman-Miner para o cálculo do Dano acumulado e comparando com dados experimentais aquisitados em simulador veicular, os resultados cálculo de fadiga demonstraram que ambas as condições de espessura atingem vida infinita. Entretanto, após a seleção e análise de algumas regiões consideradas críticas nas simulações precedentes (estampagem e estrutural), pôde-se notar que na maior parte das regiões os valores de dano acumulado eram inferiores para a condição de espessura constante. Já a condição de espessura variável se aproximou mais ao resultado medido. Pôde-se concluir com os resultados que a variação de espessura, como efeito do processo de estampagem, desempenha um papel importante na vida do componente estudado, indicando que a utilização dos dados de processo auxilia na aproximação entre os resultados do cálculo de vida e a condição real / Abstract: The simulations within the Product Development environment must give the chance to use new variables, particularly from processes, in order to improve the correlation between the virtual and real models, and thus enhance the accuracy of the simulations. The objective of this work was to study a model by the finite element method (FEM) that includes the effects of thickness variation from stamping process for the fatigue life prediction in an automotive exhaust system component. Firstly it was carried out a simulation of the stamping process, where it was possible to identify the thickness distribution all along the geometry of selected component. Then, the result of this simulation was transported to the finite element mesh, so that further analyses, structural and fatigue, could consider the effects of reduction and increasing in local thickness. As a basis for comparison, the same analyses were performed for the homogeneous geometry (uniform thickness), which are typically taken during the design phase. Using the model proposed by Wöhler-Goodman-Miner to calculate the accumulated damage and comparing with real data acquisited from a vehicle, the calculation results of fatigue showed that both conditions (equal and unequal thickness) reached infinite life. However, after the selection and analysis of some critical regions in the previous simulations (stamping and structural), it might be noted that, in most regions, the values of accumulated damage were lower for the uniform thickness condition. Besides, for the unequal thickness condition, the results got closer to those measured in vehicle. With these results, it could be demonstrated that the unequal thickness, as a process variable, plays an important role in the component life, indicating that the use of process data helps in bringing together the results from fatigue calculation and real condition / Mestrado / Manufatura / Mestre em Engenharia Automobilistica
45

Resistencia a fadiga do titanio comercialmente puro e de liga Ti-6Al-4V em diferentes meios de armazenagem / Fatigue strength of commercially pure titanium and TI-6Al-4V alloy in different storage media

Zavanelli, Ricardo Alexandre 04 September 1999 (has links)
Orientador: Guilherme Elias Pessanha Henriques / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-07-25T08:20:05Z (GMT). No. of bitstreams: 1 Zavanelli_RicardoAlexandre_M.pdf: 5267255 bytes, checksum: 6668bbd1a4fe3d55e1241b830baee2a7 (MD5) Previous issue date: 1999 / Resumo: A fadiga é responsável por 90% das falhas de infra-estruturas metálicas em serviço. Esse fenômeno está intimamente relacionado às alterações superficiais e ocorre devido à aplicação de esforços cíclicos. As PPRs sofrem fadiga devido às constantes inserções e remoções e durante o próprio ato mastigatório. Devido a propriedades como biocompatibilidade e resistência mecânica, tem-se introduzido o uso do titânio e suas ligas na confecção de coroas e próteses, sendo consideradas susceptíveis de alterações superficiais devido ao uso de soluções fluoretadas. O propósito deste estudo foi avaliar, comparar e analisar a vida em fadiga do titânio comercialmente puro e da liga Ti-6Al-4V em diferentes meios de armazenagem (sem a presença de meios; em saliva artificial; e, em saliva artificial fluoretada). Foram confeccionadas trinta amostras para cada um dos materiais, com geometria semelhante a um halteres e 2,3 mm de diâmetro na porção central, obtidas por fundição odontológica, em máquina de fundição Rematitan (Rematitan - Dentaurum J.P. Winkelstroeter KG- Pforzhein - Alemanha). O ensaio de resistência à fadiga foi conduzido numa máquina de ensaios universal (MTS - Materials Testing System, Test Star II), com carga 30% abaixo e calculada a partir do limite de escoamento a 0,2% de deformação. Após a fratura, o número de ciclos foi registrado e a superfície de fratura analisada sob microscopia eletrônica de varredura (M.E.V.). Os resultados indicaram que a liga Ti-6Al-4V obteve 21,269.50 ciclos, contra 19,157.60 ciclos para o Ti c.p., e na presença das soluções esse número diminuiu drasticamente, sugerindo provável reação dos meios com os metais. Com base nos resultados obtidos, verificamos que: A liga Ti-6Al-4V obteve os maiores valores médios de resistência à fadiga, porém sem diferença estatisticamente significante em relação ao titânio puro, independente da presença dos meios de armazenagem. A presença das soluções de armazenagem diminuiu a resistência à fadiga para ambos materiais, com diferença estatisticamente significante em relação às amostras ensaiadas sem a presença dos meios. A solução de saliva artificial fluoretada pareceu mais agressiva. Entretanto, não houve diferença estatística em relação à solução de saliva artificial / Abstract: The fatigue is responsible for 90% of metallic component failures during service. This phenomenon is closely related to superficial alteration and it occurs during cyclic stress application. Removable partial dentures (RPDs) are affected by fatigue due to cyclic mechanism of the masticatory system and the frequent insertion and removal. Because of unique and favorable properties, titanium and its alloys have been used in manufacturing crowns and bridges. However, it has been shown that preventive agents with fluoride probably affect titanium alloy surfaces. The aim of this study was to evaluate compare and analise the fatigue life of commercially pure titanium and Ti-6Al-4V alloy in different media (without media, artificial saliva and fluoride artificial saliva). For each alloy, thrirty dumb-bell rods 2.3 mm in diameter were.cast in Rematitan-System (Rematitan-Dentaurum IP. Winkelstroeter KG-Germany). The fatigue strength test was carried out with an universal testing machine (MTS- Materials Testing System - Test Star II), using a load 30 % lower than the calculated yield strength at a 0.2% offset. After failure, the number of cycles were recorded and the fracture surfaces were examined with a scanning electron microscope (S.E.M.). The mean values indicated that Ti-6Al-4V alloy achieved 21,269.50 cycles against 19,151.60 cycles for the c.p. titanium, and, when the solutions were present, the number of cycles was drastically reduced, probably due to pits caused by superficial reactions, as showed in S.E.M. analyses. It was observed that: Ti-6Al-4V alloy had the highest mean values of fatigue strenght, however, there were no siglificant differences as regards c.p. titanium. free-standing the presence or absence of media; the solutions reduced fatigue strength for both alloys, with statistically significant differences to specimens tested without the solutions; the fluoride solution was the most harmful agent, but there were no significant differences between fluoride solution and artificial saliva / Mestrado / Protese Dental / Mestre em Clínica Odontológica
46

Reliability of cold-formed steel screwed connections in tilt-and bearing

Van Wyk, Rudolf 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The South African National Standard for the structural use of cold-formed steel (SANS 10162-2) provides capacity prediction models for screwed connections. Screwed connections are designed against shear failure of the screw(s), section tear-out, net section failure and tilt-andbearing failure. Previous studies (Rogers & Hancock, 1997) showed that the capacity is typically determined by the tilt-and-bearing type failure mode. The aim of this document is to report on the reliability of single screwed connections in cold-formed steel against this critical failure mode. Predicted nominal capacities depend on the ultimate tensile strength of the steel, the thickness of the connected plates and the diameter of the screw. Design capacities are obtained by multiplying the nominal capacities by a capacity reduction factor of 0.5, according to SANS 10162-2. Reliability is assessed by means of FORM analyses, taking uncertainty in the prediction model and variability of input parameters into account. Laboratory testing of 222 single screwed connections allowed to statistically describe the model factor, i.e. the ratio of actual tested- over unbiased predicted capacity. For each connection, the steel strength, plate thickness and screw diameter were measured, with the measured values used to predict capacity. This implies that the model factor accounts for uncertainty in the prediction model and experimental setup, while the variability of input parameters is separately accounted for through appropriate statistical modelling. Variability in the input parameters was described using appropriate statistical distributions from expert literature (Holicky, 2009:199; JCSS, 2000). For steel strength, the mean value and standard deviation were obtained from tensile tests, while mean values and standard deviations of the plate thickness and screw diameter were obtained from the above mentioned measurements. The experimental work and numerical analysis resulted in a model factor with a mean just exceeding unity and a small standard deviation. This suggests that the design code under consideration is able to accurately predict the nominal capacity of screwed connections. The FORM analysis resulted in computed reliability indexes significantly higher than the corresponding target values which suggest conservative and reliable design formulations. Die eksperimentele werk en numeriese analise het gelei tot 'n model faktor met 'n gemiddeld hoër as een en 'n klein standaardafwyking. Dit dui daarop aan dat die ontwerp-kode onder oorweging in staat is om die nominale kapasitiet van skroef verbindings akkuraat te voorspel. Die betroubaarheid analise het gelei tot betroubaarheidsindekse aansienlik hoër as die ooreenstemmende teiken waardes wat daarop dui dat die ontwerp formulerings betroubaar en hoogs konserwatief is. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse Nasionale Standaard vir die strukturele gebruik van koud gevormde staal (SANS 10162-2) bied voorspellingsmodelle vir die kapasitiet van skroef verbindings. Skroef verbindings word ontwerp teen skroef faling, staal profiel faling, die uitskeer van skroewe en ook faling weens skroef kanteling. Vorige studies (Rogers & Hancock, 1997) het getoon dat die kapasiteit gewoonlik bepaal word deur die skroef-kantel falingsmodus. Die doel van hierdie navorsing is om verslag te doen oor die betroubaarheid van tipiese enkel skroef verbindings in koud gevormde staal strukture teen hierdie kritiese falingsmodus. Voorspelde nominale kapasiteite hang af van die treksterkte van die staal, die dikte van die verbonde profiele en die diameter van die skroef. Volgens die SANS 10162-2 word die ontwerp kapasiteit verkry deur die nominale kapasiteit met 'n kapasiteitsverminderingsfaktor van 0.5 te vermenigvuldig. Betroubaarheid word ontleed deur middel van ʼn eerste orde betroubaarheidsmetode analise, met die in ag neming van onsekerheid in die voorspellingsmodel en wisselvalligheid van die parameters. Laboratoriumtoetse van 222 enkel skroef verbindings het ʼn statistiese beskrywing van die model faktor toegelaat. Die model faktor is bereken as die verhouding tussen die getoetste kapasitiet en die voorspelde kapasitiet. Die staal sterkte, profiel dikte en skroef diameter is gemeet vir elke verbinding met die gemete waardes wat gebruik is om die kapasiteit te voorspel. Dit beteken dat die model faktor slegs onsekerhede in die voorspellingsmodel en van die eksperimentele opstelling in ag neem, terwyl die wisselvalligheid van die parameters afsonderlik in ag geneem word deur toepaslike statistiese modellering. Variasie in die parameters is beskryf met gepaste statistiese verdelings voorgestel deur verskeie literatuur (Holicky, 2009:199; JCSS, 2000). Aangaande die staal sterkte, is die gemiddelde waardes en standaardafwykings verkry deur standaard trek toetse terwyl die gemiddelde waardes en standaardafwykings van die plaat dikte en skroef diameter verkry is deur die bogenoemde metings.
47

Propriedades mecânicas e micromecanismos de fratura de corpos-de-prova usinados de rodas ferroviárias fundidas e forjadas / Mechanical properties and fracture micromechanisms of machined specimens from the cast and forged railway wheels

Queiroz, Syme Regina Souza 20 August 2018 (has links)
Orientador: Itamar Ferreira / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T17:14:11Z (GMT). No. of bitstreams: 1 Queiroz_SymeReginaSouza_D.pdf: 5101982 bytes, checksum: 1143c4b43c52ed713ed719367ce07ead (MD5) Previous issue date: 2012 / Resumo: A tendência mundial das estradas de ferro é utilizar carga elevada por vagão no transporte de produtos e alta velocidade no setor de passageiros. Em ambas as situações, as rodas ferroviárias são muito solicitadas mecanicamente e, em função disso, as propriedades mecânicas dessas rodas devem ser rigorosamente controladas, tendo em vista que as principais causas de acidentes envolvendo trincas nas rodas, ou a retirada da roda antes do final de sua vida, estão direta ou indiretamente associadas a baixos níveis de resistência mecânica, resistência à fadiga e tenacidade à fratura. O conhecimento do comportamento mecânico das rodas ferroviárias com base nas suas propriedades mecânicas é imprescindível para o projeto de rodas ferroviárias e para o aprimoramento de seu processo de fabricação. Este trabalho tem como objetivo caracterizar e analisar a microestrutura, as propriedades mecânicas e os micromecanismos de fratura de cinco rodas ferroviárias, duas fundidas e três forjadas, a partir de corpos-de-prova usinados dos aros e discos dessas rodas. As propriedades mecânicas analisadas são as básicas (limite de escoamento, limite de resistência à tração, alongamento específico até à fratura, redução de área, dureza e energia de impacto Charpy), a resistência à fadiga e a tenacidade à fratura, de corpos-de-prova usinados das rodas ferroviárias. Além das microestruturas e das propriedades mecânicas, foram também caracterizados e analisados os micromecanismos de fratura dos corpos-de-prova dos ensaios de fadiga e impacto, por meio de microscopia eletrônica de varredura. Os resultados dos ensaios indicam, em relação aos limites de escoamento e de resistência à tração, que não houve diferenças significativas entre as rodas fundidas e forjadas analisadas. Quanto à dureza (HRC), ductilidade (alongamento específico e redução de área) e tenacidade à fratura, as rodas forjadas apresentaram valores superiores. Em relação à resistência à fadiga, uma propriedade importante no caso de rodas ferroviárias, os corpos-de-prova usinados das rodas forjadas apresentaram melhores resultados em relação às rodas fundidas. Pode-se também concluir que, tanto para as propriedades mecânicas básicas e nobres como também para os micromecanismos de fratura, os resultados obtidos são compatíveis aos encontrados na literatura especializada, validando e comprovando que a metodologia de análise pode ser utilizada para melhorar os projetos e os processos de fabricação de rodas ferroviárias de aço fundidas e forjadas / Abstract: The word wide tendency of railroads is to use high load per wagon in cargo transport and high-speed in passenger sector. In both situations, the railway wheels are very mechanically requered, and as a result, the mechanical properties of these wheels should be controlled strictly in order that the main causes of accidents involving wheels cracks, or withdrawal of the wheel before end of its life, are directly or indirectly associated with low levels of strength, fatigue resistance and fracture toughness. Knowledge of the mechanical behavior of railway wheels based on their mechanical properties is essential for the design of railway wheels and the improvement of its manufacturing process. This work aims to characterize and analyze the microstructure, mechanical properties and fracture micromechanisms of five railway wheels, two cast and three forged, from the machined specimens of the rim and web of these wheels. The analyzed mechanical properties are the basics (yield strength, tensile strength, elongation, reduction in area, hardness and Charpy impact energy) the fatigue resistance and the fracture toughness, from the specimens machined of railway wheels. In addition to the microstructures and mechanical properties were characterized and analyzed the micromechanisms of fracture of the specimens of fatigue and impact tests, using scanning electron microscopy. The test results indicate, with respect to the yield strength and tensile strength, there were no significant differences between cast and forged wheels analyzed. The hardness (HRC), ductility (elongation and reduction in area) and fracture toughness of the forged wheels showed higher values. Regarding resistance to fatigue, an important property in the case of railway wheels, the forged wheels machined specimens shown better results compared to cast wheels. One can also conclude that, for both the basic and noble mechanical properties as well as for the micromechanisms of fracture, the results are compatible with those found in the literature, validating and verifying that the method of analysis can be used to improve the castings and forgings steel railway wheels and manufacturing processes and projects / Doutorado / Materiais e Processos de Fabricação / Doutora em Engenharia Mecânica
48

Microstructure-sensitive plasticity and fatigue of three titanium alloy microstructures

Smith, Benjamin Daniel 21 October 2013 (has links)
Titanium alloys are employed in many advanced engineering applications due to their exceptional properties, i.e., a high strength-to-weight ratio, corrosion resistance, and high temperature strength. The performance of titanium alloys is known to be strongly affected by its inherent microstructure, which forms as a result of its thermo-mechanical processing. These microstructures produce compromise relationships between beneficial and detrimental effects on the alloy's performance. To study these structure-property relationships, two distinct crystal plasticity algorithms have been calibrated to data acquired from cyclic deformation experiments performed on three different Ti microstructures: (1) Ti-6Al-4V beta-annealed , (2) Ti-18 solution-treated, age-hardened (STA), and (3) Ti-18 beta-annealed, slow-cooled, age-hardened (BASCA). The calibrated models have been utilized to simulate fatigue loading of variant microstructures to investigate the influence of mean grain size, crystallographic texture, and phase volume fraction. The driving force for fatigue crack nucleation and propagation is quantified through the calculation of relevant fatigue indicator parameters (FIPs) and radial correlation functions are employed to study the correlation between favorably oriented slip systems and the extreme value FIP locations. The computed results are utilized to observe fatigue performance trends associated with changes to key microstructural attributes.
49

An in situ test for stress corrosion damage and tension in bolts

Barke, Derek Woolrich, 1975- January 2002 (has links)
Abstract not available
50

Stress corrosion cracking of X65 pipeline steel in fuel grade ethanol environments

Goodman, Lindsey R. 20 August 2012 (has links)
In recent years, the demand for alternatives to fossil fuels has risen dramatically, and ethanol fuel has become an important liquid fuel alternative globally. The most efficient mode of transportation of petroleum-based fuel is via pipelines, and due to the 300% increase in ethanol use in the U.S. in the past decade, a similar method of conveyance must be adopted for ethanol. Low-carbon, low-alloy pipeline steels like X52, X60, and X65 comprise the existing fuel transmission pipeline infrastructure. However, similar carbon steels, used in the ethanol processing and production industry, were found to exhibit stress corrosion cracking (SCC) in ethanol service. Prior work has shown that contaminants absorbed by the ethanol during distillation, processing or transport could be the possible determinants of SCC susceptibility; 200 proof ethanol alone was shown not to cause SCC in laboratory studies. To ensure the safety and integrity of the pipeline system, it was necessary to perform a mechanistic study of SCC of pipeline steel in fuel grade ethanol (FGE). The objective of this work was to determine the environmental factors relating to SCC of X65 steel in fuel grade ethanol (FGE) environments. To accomplish this, a systematic study was done to test effects of FGE feedstock and common contaminants and constituents such as water, chloride, dissolved oxygen, and organic acids on SCC behavior of an X65 pipeline steel. Slow strain rate tests (SSRT) were employed to evaluate and compare specific constituents' effects on crack density, morphology, and severity of SCC of X65 in FGE. SCC did not occur in commercial FGE environments, regardless of the ethanol feedstock. In both FGE and simulated fuel grade ethanol (SFGE), SCC of carbon steel was found to occur at low water contents (below 5 vol%) when chloride was present above a specific threshold quantity. Cl- threshold for SCC varied from 10ppm in FGE to approximately 1 ppm in SFGE. SCC of carbon steel was inhibited when oxygen was removed from solution via N2 purge or pHe was increased by addition of NaOH. During SSRT, in-situ¬ electrochemical measurements showed a significant role of film rupture in the SCC mechanism. Analysis of repassivation kinetics in mechanical scratch tests revealed a large initial anodic dissolution current spike in SCC-causing environments, followed by repassivation indicated by current transient decay. In the deaerated environments, repassivation did not occur, while in alkaline SFGE repassivation was significantly more rapid than in SCC-inducing SFGE. Composition and morphology of the passive film on X65 during static exposure tests was studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results showed stability of an air-formed native oxide under static immersion in neutral (pHe = 5.4) SFGE, and dissolution of the film when pHe was decreased to 4.3. XPS spectra indicated changes in film composition at high pHe (near 13) and in environments lacking sufficient water. In light of all results, a film-rupture anodic-dissolution mechanism is proposed in which local plastic strains facilitates local breakdown of the air-formed oxide film, causing iron to dissolve anodically. During crack propagation anodic dissolution occurs at the crack tip while crack walls repassivate preserving crack geometry and local stress concentration at the tip. It is also proposed that SCC can be mitigated by use of alkaline inhibitors that speed repassivation and promotes formation of a more protective Fe(OH)3 film.

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